Reinforced Soil and Application inInfrastructure Development

Proceeding of the National Conference on 'Geotechnical and Geoenvironmental

Aspects of Wastes and Their Utilization in Infrastructure Projects' held at

Guru Nanak Dev Engineering College Ludhiana, India, 15-16 February, 2013

Dr. J. N. JhaDepartment of Civil Engineering, Guru Nanak Dev Engineering College, Ludhiana

Dr. Harvinder SinghDepartment of Civil Engineering, Guru Nanak Dev Engineering College, Ludhiana

Prof. K. S. Gill Department of Civil Engineering, Guru Nanak Dev Engineering College, Ludhiana

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National Conference on

Aspects of Wastes and Their Utilization in Infrastructure Projects

(GGWUIP-2013)

15th & 16th February 2013

Editor

J.N.JhaHarvinder Singh

K.S.Gill

Organised by

Department of Civil EngineeringGuru Nanak Dev Engineering College

Ludhiana

In Association with

Indian Geotechnical Society-Ludhiana ChapterTesting and Consultancy Cell, GNDEC Ludhiana

Geotechnical and Geoenvironmental

First Impression : 2013

Guru Nanak Dev Engineering College, Ludhiana.

National Conference on Geotechnical and Geoenvironmental Aspects of Wastes and Their Utilization in Infrastructure Projects

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PREFACE

India with over 1 billion population is rapidly emerging as superpower and set the target of

becoming a developed nation by the year 2020 thereby, the immediate major focus is on the infrastructure

development. As a result, lot of industrialization and urbanization is taking place all around the country.

Due to rapid urban and industrial development, large quantities of wastes are being generated and disposal

of these wastes in landfill is not a sustainable solution in the long term due to limited availability of land

space. Many urban centres in India are already facing problems of finding adequate land for disposal of

waste for the next 25 to 50 years. Many of the geo-environmental challenges caused by the improper waste

disposal practice in developing countries like India resulted in producing huge quantities of green house

gas emissions. The resulting effect on climate change can be felt world over. Therefore the waste

management has now become a matter of great concern in India and other developing nations. The most

suitable long term sustainable solution is to reduce the quantity of waste being produced and eventually

become a 'zero waste' society. Waste reduction can be achieved through adoption of efficient and clean

technologies which produce the same quantities of usable products with much smaller quantities of waste

and also by recycling or through re-use of waste material generated. Some example of recycling and re-use

of waste material are conversion of organic waste into compost, use of fly ash as pozzolonic material, use of

slag in construction of sub base courses of roads, use of waste material in geotechnical and other

infrastructure development.

Under this backdrop, Civil Engineering Department of Guru Nanak Dev Engineering College,

Ludhiana (An autonomous college under UGC act) in association with Indian Geotechnical Society:

Ludhiana Chapter and Testing and Consultancy Cell, Guru Nanak Dev Engineering College Ludhiana is

organizing a two day (February 15-16, 2013) National Conference on “Geotechnical and Geo-

environmental aspects of Wastes and their Utilization in Infrastructure Projects”. The conference is

focusing on the advances being taking place in geotechnical and Geo- environmental aspects of wastes so

that it can meet the requirement for their utilization in infrastructure development. The sub-themes of the

conference have divided accordingly and have great relevance for waste utilization in infrastructure

projects. About 15 speakers from academia and industries have agreed to deliver expert lecture during the

conference. In addition 75 papers have been selected out of 163 abstracts received from different part of the

country.

We are particularly thankful to the Department of Science and Technology (DST), GOI; Council

of Scientific and Industrial Research (CSIR), GOI; and Technical Education for Quality Improvement

Programme (TEQIP-II), a world bank sponsored Project of MHRD, GOI for associating themselves with

this conference. We also appreciate and extend hearty thanks to TATA TISCON, main sponsor of the

conference and HEICO, AIMIL Ltd., and AKSS Consultants and Engineers, co-sponsor to this conference

for their liberal financial assistance. We have also received financial support from several other

organizations, agencies and individuals, our salutation are to them for supporting this event. We also hope

that the participants will return to their destination fully satisfied with the deliberations of the conference.

We do hope that this conference will rejuvenate the Civil Engineering Department to conduct many more

such events in future.

Feb’2013Ludhiana

Jagadanand Jha Harvinder Singh

Kulbir Singh Gill

Collaborating Institutions

Indian Geotechnical Society: Ludhiana Chapter.

Testing & Consultancy Cell, GNDEC Ludhiana.

Sponsoring Organisations

Department of Science & Technology, New Delhi.

Council of Scientific and Industrial Research, New Delhi.

TEQIP-II

TATA TISCON

HEICO, New Delhi.

AIMIL, New Delhi.

MRH Associates, Ludhiana.

AKSS Consultants, Bathinda.

Future Fibres and Filaments, Ludhiana.

Kalsi Construction and Engineers, Ludhiana.

Ceigal India Ltd, Chandigarh.

Deepak builders Pvt Ltd, Ludhiana.

J K Infcon Pvt Ltd, Ludhiana.

Gupta Enterprises, Ludhiana.

Gandwana Engineers, Nagpur.

Virindra Buidcon Pvt Ltd, Chandigarh.

Royal Builders Pvt Ltd, Mall Road, Ludhiana.

CONTENTS

Load bearing behavior of ash fillsAshutosh Trivedi (Key Note Speaker)

1 Innovative contracting for speedy construction 255S. Unnikrishna Pillai

2 An insight into the geotextile - municipal solid waste interface 263characteristicsS. K. Shukla, A. K. Singh and J N Jha

3 Selection of suitable strategies for rehabilitation of 268flexible pavementsSanjeev Aggarwal

4 Recycled aggregates: - An overview 277Pinal Saini, Jagbir Singh and Rajesh Kumar

5 Evaluating liquefaction behavior of solani sand 283Rajiv Chauhan

6 Seismic modeling in soil structure interaction continuum 290Harpal Singh

7 A case study of closely spaced exactly identical structures with different 296foundations on expansive soilA Kameshwar Rao, S M Jalali, Sneha Rao, Rahul Patidar and Priyanka Jain

8 Bearing capacity of shallow foundation on slope: A review 301Dhiraj Raj, M. Bharathi

9 Raft foundations at the end of early years 321Prashant Garg, J N Jha and Harvinder Singh

10 Tire shreds reduce earth pressure on earth retaining structures 330S. Bali Reddy and A. Murali Krishna

11 Municipal solid waste management in goa – Aa cse study 335M. Anwakar, S. Shaikh, P. Sayoikar

12 Damage identification and behavior of slabs using external laminates: 343A review paper H K Gaba, H S Rai, S P Singh

13 Seismic microzonation – A study 349Rajiv Chauhan and Surender Singh

14 Char Waste As Road Material- A Case Study 356K. G. Guptha, S.A. Kakodkar

15 Biomedical Waste Treatment Facility 367Sasmita Sahoo

16 Effect Of Reinforcement On Fly Ash Slope 375Parveen Chander, Jasbir Singh, Rajesh Kumar and J N Jha

Page

17 Experimental investigations on self- compacting concrete 385using brick dust and coal ash as fine aggregate replacementRakhjinder Singh and KS Bedi

18 Development of self compacting concrete using rice 391husk ash as a supplementary cementing materialGurbir Jawanda

19 Shear strength characteristics of self compacting 400concrete using flyash and silica fumeKanwarjeet Jeet Singh Bedi, Rajesh Kumar and Harpreet Kaur

20 Optimum design of geosynthetic reinforced soil foundation 412Using Genetic AlgorithmSiddharth Das, Manas Ranjan Das and Sarat Kumar Das

21 Analytical study on the benefit of sisal fibre reinforcement 422of expansive clayey subgrade using fem

Binu Sara Mathew and Gayathri Mohan

22 Compaction and CBR behaviors of clay reinforced 430with NAOH treated coir fibresR K Dutta, Vishwas Nandkishor Khatri and V Gaythari

23 Reinforced coal ash slope: Experimental investigations 439Vikramjit Singh, K S Gill, J N Jha and Amandeep Singh

24 Improvement in CBR value of clayey soil by use of Geo-grid layers 447Rajiv Kumar, Gurdeepak Singh and B S Walia

25 Experimental investigation on slope stability using soil nailing technique 451S.Boobathi Raja, M.Ganeshram and A.Kavitha

26 Investigation on crumb rubber modified concrete: An overview 459J. Parveen, Sachin Dass and Ankit Sharma

27 Bearing capacity behavior of strip footings on reinforced slope: 465Numerical ApproachAmandeep Kaur

28 Computational modelling of soil nail walls: A case study 473V.P. Singh

29 Load test on multilayer reinforced coal ash slope 481Gurdeep Singh, K S Gill and J N Jha

30 Strength behavior of reinforced pond-Ash cement mix 488Karanbir Singh, J N Jha, K S Gill

31 CBR improvement of clayey soil using geogrid reinforcement 495Pardeep Singh

CONTENTSPage

CONTENTS

32 Utilization of waste polymer in construction of flexible pavement 501M. Mohanty, M. Panda and U. Chattaraj

33 Utilization of plastic wastes and waste recycled product 509in flexible pavement systemA K Choudhary, Ranjit Prasad and K S Gill

34 Tests on uncontrolled burnt rice husk ash and cement mix 517H K Khullar, K S Gill, Harvinder Singh and J N Jha

35 Construction over closed landfill 523P Y Sarang, P P Savoikar and C S Gokhle

36 Effects of chemical admixture on setting and strength properties of 532FaL-G BlocksS P Singh, J K Naik and S Tripathy

37 Construction and environmental issues 538Ramandeep Kaur, Sarpreet Singh and Manpreet Singh

38 FaL-G: An alternate building material 544Sanjeev Naval et al

39 Improvement of sub-grade using quarry dust waste 550Prashant Garg and Gurcharan Singh

40 Biomedical waste management: Indian scenario 556Amanpreet Singh Virk, Manjeet Bansal and Gurpreet Singh Bath

41 Mechanical properties of high volume flyash concrete at 562elevated temperaturesInderpreet Kaur, Umer Farooq and Harshdeep Singh

42 Climate responsive building design using efficient building form, 573orientation and passive techniquesJatinder Kaur, Ripu Daman Singh

as highway materials

Page

Key Note

LOAD BEARING BEHAVIOR OF ASH FILLS

Ashutosh Trivedi Professor, Department of Civil Engineering,

Delhi Technological University, Bawana Rd., Delhi, India, 110042. E-Mail: atrivedi@dce.ac.in

Abstract: The ash material often disposed as fly ash or coal ash is a normal by-product of all the coal fired thermal power plants. It is extensively deposited as a landfill on a low lying area and used as an embankment fill. Many of these fills remain vulnerable to the problem of excessive deformation namely collapse, erosion and liquefaction. These landfills may be used as a structural fill if the ash is properly characterized and compacted. To improve its performance as a structural fill, ash is normally compacted by vibration on wet of optimum. Few of the characteristics of un-cemented ash fills are found similar to cohesion less soil. In the present study, experimental investigations for characterization, collapse, bearing capacity and settlement are evaluated for the coal ash. The bearing capacity and settlement prediction is based on the settlement of rigid plates on ashes compacted at varying degree of compaction. The bearing capacity and settlement based on the experimentally observed data on ash using conventional techniques of investigation for soils was found unsuitable. A plot for bearing capacity factor and settlement is proposed for compacted ash. The settlements at lower values of CPT and SPT and that in saturated condition would remain vulnerable to excessive settlement as also reflected by the collapse. It is shown graphically that at a lower degree of compaction and higher degree of saturation, the settlement exceeds the allowable settlements.

INTRODUCTION

Coal based power is one of the heavily relied means of power generation throughout the world. One of the continuing practices throughout the countries has been to consider the disposal of ash, by often dumping into an area previously considered a wasteland. The recent studies [Cousens and Stewart, 2003, Prakash and Sridharan, 2009, and Locour, 2012] indicate potential vulnerability of the ash fills. But the land reclamation using coal ash is viably investigated in various parts of the world. Moreover, it has been a matter of interest among scientific community to explore the engineering behavior of a lightweight fill material such as coal ash [Sridharan et al. (1998, 2001), Trivedi et al. (1999), Trivedi and Sud, (2002, 2004, 2007), Trivedi and Singh, (2004 a,b) and Choudhary et al. (2010)].

In the present study, coal ash was considered from Ropar thermal plant in Punjab, India. The composite ash collected from electrostatic precipitators of thermal power plant may be classified as fly ash. The coal ash produced from furnace bottom, known as bottom ash, is around 20 to 25 % of the total ash produced. The composite ash is disposed into a pond by mixing it with the bottom ash and water to form slurry. The slurry usually contains 20 % solids by weight. This method of ash disposal is called wet method. The landfill of ash may be used as a construction fill if the suitable ashes are properly compacted. The fine ashes may collapse upon wetting. To avoid excessive settlement upon wetting suitability of coal ash should be examined as per the criteria of collapse [Trivedi and Sud, (2002, 2004)] and liquefaction [Trivedi et al. (1999), Day and Gandhi (2008)].

Key Note

The chemical and physical characteristics of the ash produced depend upon the quality of coal used, the performance of washeries, efficiency of the furnace and several other factors. The physical and chemical properties of ash are influenced by the type and source of coal, method and degree of coal preparation, cleaning and pulverization, type and operation of power generation unit, ash collection, handling and storage methods, etc. Ash properties may vary due to changes in boiler load. The choice of furnace type such as stoker fired, cyclone type or pulverized coal furnace is also known to affect properties of ash collected. During the combustion of coal, above minerals are transformed to mullite, magnetite, tridymite, glass, etc. thus forming a composite ash. The main chemical components of coal ash are silica, alumina, iron oxide and other alkalis. The mineral group present in coal, such as hydrated silicate group, carbonate group, sulphate group and their varying compositions play a major role in determining the chemical composition of ash. As per the source of coal used by in different countries, the chemical composition (Mishra and Das, 2010) and design parameter [IRC, (2001) and Lacour, (2012)] of the ashes are different (Table 1a).

Table 1- Design parameters for coal ash

Parameter Range (IRC, 2001) Trivedi & Sud (2002, 2004), Trivedi & Singh (2004a, b)

Sp. gravity Plasticity Maximum dry unit weight OMC

1.90-2.55 NP 9-16 38-18%

1.70-2.6 NP 8-18 20-40%

Cohesion negligible Nil Angle of internal friction 30-40 27-46 Coefficient of consolidation cv (cm2 sec-1)

1.75x10-5-2.01x10-3 -

Compression index (cc) 0.05-0.4 0.01-0.006 Permeability (cm sec-1) 8x10-6-7x10-4 1-7 x 10-5

Particle size distribution Gravel Sand Silt Clay

1-10% 8-85% 7-90% 0-10%

5% 10-90% 10-90% 0-5%

Coefficient of uniformity 3.1-10.7 2-12

The ASTM classifications of coal ash are related to the percentage of calcium oxide in ash. The ashes with high amount of calcium oxide show self-hardening pozzolanic properties in presence of water. The pozzolanic properties of fly ash have been documented by Mehta and Monterio (1997). Such ashes are designated as class C ash. A typical class C ash is obtained from the burning of lignite coal. The ashes from bituminous coal, that do not possess self-hardening properties, are called class F ash. The ash produced at Ropar may be classified as class F. Coal ash is normally used in the construction of ash dykes, reclamation of low lying land, man-made earth structures such as embankments, road fills, etc. The landfill intensive utilization of coal ash requires stability analysis of fill. General recommendation by IRC for the use of ash in embankment is as follows

o Fly ash to be used as fill material should not have soluble sulphate content exceeding 19 kNm-3 (expressed as SO3) when tested according to BS: 1377.

Key Note

o Coal used in Indian thermal power plants has high ash content. As a result, enrichment of heavy metal is lower as compared to fly ash produced by thermal power plants abroad.

Detailed design recommended by IRC for the use of ash in embankment is as follows.

o The design of fly ash embankment is similar to earthen embankments. o Special emphasis is required with respect to provision of earth cover. o The thickness of side cover would be typically in the range of 1 m to 3 m. o For embankment up to 3 m height, in general, the earth cover thickness about 1 m is

sufficient o The side cover should be regarded as a part of embankment for design analysis. o The factor of safety for embankments constructed using fly ash should not less than 1.25

under normal serviceability conditions. o Intermediate soil layers are often provided in the fly ash embankment for ease of

construction to facilitate compaction of ash and to provide adequate confinement. o Properly benched and graded slopes prevent the erosion of fly ash particles. As a result of vide ranging studies, it is well realised that ash needs especial engineering

considerations for its use as an engineering fill.

REVIEW OF PREVIOUS WORK

Some of the case studies are reported on investigation and assessment of load bearing behavior of coal ash which is relevant to its uses in embankment fills also. These tests are namely penetration tests and plate load test as described below.

PENETRATION TEST

The standard and cone penetration devices are used to evaluate the stability of a landfill. The standard penetration test is used in different parts of the world with slight variation in the version of its use. It involves estimation penetration value of 300 mm run of a split barrel of 50(±2) mm external and 35(±1) mm internal diameter under impact of 63.5kg hammer. Cunningham et al. (1977) reported the results of standard penetration tests (SPT) conducted on hydraulically deposited Illinois ash. The penetration was observed to be of several stretches of 30 mm under the weight of drill rods to 9 blows per 300 mm of penetration. The SPT value for compacted Kanawha ash was observed among 10 and 31 and had an average of 19.5 for seventeen independent tests conducted in four borings excluding the values obtained for lenses of bottom ash. Dry density values determined for five of the nine Shelby tube samples taken from these bore holes suggest hardly a correlation with the N-values. Field dry density was found between the limits of 95 % to 100 % of the Proctor density (14.86 to 15.93 kN/m3). The average cone penetration resistance (in kg/cm2) was found to be twice of SPT value. Ashes normally in silt size, especially in loose condition, may liquefy under the tip of penetrometer below water table resulting in a lower penetration record. For the compacted ash fills, density projection and SPT (N) number is presented in Table 2. These low values of N are partly associated with a low unit weight and partly with a high percentage of fines and a high moisture condition. A high value of N is partly associated with the presence of lenses of bottom ash and partly with a high degree of compaction. Seals et al. (1977) reported an average friction ratio for sleeve and ash from 3 to 4.7 slightly higher than the value cited by Schmertmann (1970) for clay silt sand mixes, silty sands, silts and sands. Toth et al., (1988) quoted a wide variation in SPT value ranging from 10-55 in fly ash with angle of internal friction 35 to 36°. The empirical co-relation between SPT values and φ (angle of internal friction) for natural soils (Peak et al. 1974) in this range of SPT value (N = 10 to 55) indicated angle of internal friction between 30 to 45°. The investigations carried out by Cousens

Key Note

and Stewart (2003) for the range of cone resistance and the friction ratio (200 kPa and 8 % respectively) indicated grain sizes in the range of silt (60-80 %) and clay (5-10 %). For a target relative density (50 to 85 %) variation in standard cone resistance is among 2000 to 6000 kPa. However the average friction (between sleeve/cone and ash material) ratio was observed to be 3 to 5% (Trivedi and Singh, 2004). The settlement of these ash fills on the basis of Schmertmann method was found to be a non-conservative estimate.

Table 2- Variation of SPT value for ash deposits

Ash Type Dc (%) N-value Reported by Compacted Kanawaha ash 95-100 10-31 Cunnigham et. al.,

1977 Well compacted Ontario flyash 85-100 10-55 Toth et. al., 1988

Compacted ash dyke 95 4-27 Dayal et.al.,1999 Hydraulically deposited ash Loose state Zero Dayal et.al.,1999 Hydraulically deposited ash Loose state Zero-1 Sood et. al., 1993 Hydraulically compacted ash Dense state 1-10 Sood et. al., 1993

LOAD TEST

On the basis of a case study on Indianapolis ash, Leonards and Bailey (1982) suggest that load settlement relation for foundation on compacted ash cannot be inferred from standard penetration test or static cone penetration tests. It is largely attributed to the inadequacy of penetration tests to sense the effect of compaction related pre-stressing of coal ash. The predicted settlements for a selected footing 2.1-m wide at design pressure of 239 kPa on well compacted ash from the data of SPT as five times, and CPT as three times of that of plate load test (PLT).

The plate load test results on compacted ash compared with Terzaghi and Peck (1948) results for very dense sand (N = 50 blows/305 mm penetration) indicated that ash materials are significantly less compressible in the pressure range of interest. At 100 kPa, compacted ash may settle less (0.6-mm) compared to the settlement of same plate on sand (approximately 1.2 mm).

Toth et al. (1988) reported a case study on performance of Ontario ash (a typical ASTM class F ash). During the compaction of ash as a landfill it was observed that the densities being achieved in the field were normally below 95 % of maximum Proctor density. On the basis of good bearing capacity observed in plate load test, Crag and Chan (1985) recommended 90 % of maximum Proctor density as the target density for the fly ash landfills. Toth et al. (1988) obtained short term and long-term test results for circular plates of 0.3-m and 0.6-m diameter. The settlements for long-term tests occurred within the first hour of load application.

Results of investigations by various investigators are given in Table 4. The tests conducted on a common degree of compaction (93.4%) and plate size (600-mm diameter) had different settlement records at stress level of 100 kPa (2.61 and 3.59 mm). Trivedi and Sud (2004) have shown that the variation in grain sizes the ashes may result in to different settlement characteristics even at a common degree of compaction. Trivedi and Singh (2004) reported higher load bearing capacity of ash fills than actually estimated by cone resistance.

Key Note

CHARACTERIZATION

X-ray diffraction study was carried out to identify the mineral phases present in the ash. X-ray diffraction showed that the ash contains traces of aluminum silicate, quartz and some heavy minerals like hematite and magnetite. Identification of definite crystalline mineral was based on Bragg’s equation,

λ = 2 d sin 2θ, (1)

where λ is wavelength of x-ray specific to the Cu target element (= 1.542Å) and d is inter planner spacing. The test was conducted between 0°-70° (2θ), at a rate of 0.8°/sec using the CuKα characteristic radiation of Cu target element. The inter planner spacing of respective peaks on the x-ray pattern were calculated from the corresponding 2θ angle. These peaks were associated with the characteristic minerals. In crystalline form, ash contains traces of aluminum silicate, quartz and some heavy minerals (Fig.1; Trivedi and Sud, 2002).

Fig.1-X-ray diffraction pattern of a typical ash sample

The potential clay minerals may be present or absent in the ash (Table 1a) indicating that ash may or may not have any structural cohesion in natural state. The any peak associated with hydrated calcium silicate group that is responsible for the development of cohesion due to pozzolanic reaction (marked by the formation of crystals of hydrated calcium aluminum silicate compound on curing in presence of water with time) indicates self-hardening properties of ash. Therefore, absence or presence of coal ash may be classified as cohesionless soil or cemented soil mass while evaluating its behavior as an engineering fill.

Ash samples contain distinguishable amount of amorphous phase. It was seen that amorphous phase is in highest amount in pond ash among all ash types. It is because of presence of unburned coal in bottom ash component. Comparing the X-ray diffraction pattern of ash samples with sand (cohesion less) it is understood that sand is characterized by the presence of peaks associated with crystalline quartz, while the ash is characterized by the presence of peaks associated with quartz as well as humps of non-crystalline matter. Burning of coal at high temperature and sudden cooling of ash in a small interval of time produced non-crystalline matter in coal ash.

The presence of glassy phase, which is non-crystalline in nature, is around 60 to 88 % of ash by weight (Leonards and Bailey, 1982; Mehta and Monterio, 1997). It is observed that the cohesionless soils of similar gradation as that of ash may be characterized as sandy silt to silty sand. These soils have dominant presence of crystalline quartz. The presence of some amorphous matter along with crystalline quartz may have induced certain difference in ash.

Key Note

CHEMICAL COMPOSITION

The chemical composition of the ashes was obtained from the non-combustible components produced by burning of the coal. The comparison of a typical range of chemical composition of ashes from different parts of the world along with the Ropar ash is given in Table 1. The main constituent of the Ropar ash was silica followed by alumina, oxides of iron and calcium. The presence of sodium and potassium salts was known by the qualitative chemical analysis. The submergence of ashes was critical compared to the other granular soils due to the presence of these soluble matters. The solubility of ash sample was determined separately at the boiling water and the room temperature. Each sample was thoroughly mixed with the boiling water by a stirrer. The entire experiment was repeated with the cold-water mix at the room temperature. This mixture was filtered through the whatman-42 filter paper. The retained ash was dried in an electric oven at 105º for 24 hours and the percentage soluble in the ash was obtained. The pond ashes had no soluble content while fine ashes obtained directly from electro static precipitator were found to have significant percentage of soluble.

Table 3- Settlement of test plate on compacted ash fill Plate size

(mm) Degree of Compaction

(%) S/B at100

kPa Interpolation from

900, square 85.24 0.56 Trivedi & Sud, 2007 600, square 85.24 0.63 Trivedi & Sud, 2007 300, square 85.24 0.45 Trivedi & Sud, 2007 300, square 90.29 0.35 Trivedi & Sud, 2007 600, square 90.29 0.40 Trivedi & Sud, 2007 900, square 90.29 0.34 Trivedi & Sud, 2007 600, circular 98.20 0.23 Toth et.al., 1988 300, circular 98.20 0.15 Toth et.al., 1988 600, square < 95% 0.22 Leonards and Bailey, 1982 300, square < 95% 0.23 Leonards and Bailey, 1982

MICROSCOPIC STRUCTURE

Fig. 2- Electron micrograph of a typical ash sample

The micrographic investigation of ash samples is presented in Fig.2. Electron micrograph of PA1 sample indicates presence of predominantly coarse grain particles while that of PA2 indicates finer particles. It also suggests that coarse ash contain rounded spherules, sub-rounded, and opaque particles. Ash sample contain superfine that form agglomerates which had a tendency to stick together and appear as larger particle upon pressing. Observing ash with microscope it is seen that ash particles are clear or translucent spherules (siliceous aluminous particles), sub rounded and

Key Note

rounded porous grains, irregular agglomerated glass spherule, opaque dark gray and red angular grains of magnetite and hematite, and black porous grains of carbon.

GRAIN SIZE DISTRIBUTION

Grain size distribution of different ash sample is given in Fig.3. Ash contains particle size in the range of coarse sand to silt. However, the maximum frequency of particle is in the range of fine sand to silt. Pond ash, which was examined for mass behavior, contains 5 to 10 % of particle in coarse and medium sand size, 35 to 50 % in fine sand size and 40 to 60 % of particles in the range of silt. Presence of superfine (size ~ 0.01 mm) increases inters particle friction, agglomeration and formation of pendular bonds in presence of moisture.

APPARENT SPECIFIC GRAVITY

Coal ashes have much lower apparent specific gravity than the natural soils of similar gradation that is largely composed of α and β quartz, cristobalite and tridymite. The ash contains maximum percentage of silica among all the constituents. A low value of the specific gravity was attributed to the trapped micro bubble of air in the ash particle and the presence of unburned carbon. Air voids percentage of ash (5 to 15%) was found to be greater than natural soils (1 to 5%) at maximum dry density (Moulton 1978). It was noticed that as fineness of the ash increases, the specific gravity also increases (Table 5a) partly due to the release of entrapped gases. Webb (1973) and Leonards and Bailey (1982) reported a similar phenomenon in the ash grounded by mortar and pestle indicating possibility of breaking of bigger particles only.

The mineralogical composition is one of the other reasons for variation in the specific gravity of the ash relative to soils. The ashes with high iron content tend to have a higher specific gravity. Pandian et al. (1998) found that the presence of heavier minerals such as hematite and magnetite result into a higher specific gravity. Seals et al. (1972) indicated that the bottom ash typically had a higher specific gravity. The pond ash (PA1 & PA2) had a higher specific gravity than the other samples. It was partly due to the presence of bottom ash in the pond, which contains heavier components of the coal ash. Some of the ash solids contain pores, which are not interconnected, and hence they possess, on measurement, less specific gravity, although the specific gravity of constituent mineral remains in the usual range. In such cases it is referred as apparent specific gravity, which is based on the weight in air of a given volume of ash solids, which includes the isolated voids.

Fig. 3-Grain sizes present in coal ashes

Key Note

COMPACTION

In the design of ash dykes and ash fills, it is desirable to consider the compaction characteristics of the ashes. The hydraulically disposed ash in the ash ponds is normally in a low-density state. In order to improve its engineering properties compaction is required. Coal ash may be compacted by vibration due to its non-plastic nature. However, owing to significant percentage of fines it may be compacted by impact. A granular material may be placed in varying states of density i.e. loosest state or in dense states.

The void ratio of ash sample in the loosest state was obtained by a slow pouring technique. The ash was poured in a fixed volume mold from a constant height of fall of 20mm. In vibration test, ash was deposited at varying moisture contents in a standard thick walled cylindrical mold with a volume of 2,830 cm3. The ash was vertically vibrated at double amplitude of 0.38mm for seven minutes in this mold mounted on a vibration table with a frequency of 60 Hz. Difficulties of flow of the fines were encountered in using this technique. The capping plate was modified to fit at the top of the mold so that it presses the ash with least a clearance in the side. Double amplitude of vertical vibration of 0.38 mm was found to be optimum for ash samples.

Fig.4 shows the results of the proctor compaction tests on the ash sample. The result of proctor compaction of the ashes with varying gradation indicates reduction in water requirement to achieve maximum density with fineness. The increasing fineness demonstrates a sharp increase in maximum dry density in proctor test (Fig.4).

Table 4- Specific gravity, Procter density and optimum moisture content

Ash Type Specific Gravity Maximum Dry Unit Weight (kN/m3)

Optimum Moisture Content (%)

MH 1.90 11.7 33 PA-1 1.98 9.50 40 PA-2 2.00 10.3 37.5

Table 5- Results of vibratory and Proctor compaction

Ash Type

γdmin emax γd

max (Dry)

γdmax

(Wet)

emin (Dry)

emin (Wet)

γdmax

Proctor Void Ratio

at γd

maxProctor PA-1 7.63 1.6 9.56 9.50 1.06 1.08 9.5 1.08 PA-2 7.85 1.54 10.56 10.3 0.89 0.94 10.3 0.94

Normally, the density in the vibration test was lower than that in the proctor test in the dry side of optimum due to the rebound action of the spherical ash particles at a low degree of saturation. In the vibration test a reduction in the density was observed with moisture content contrary to the proctor test. It was due to the slacking of ash at a low saturation level. The minimum value of the dry unit weight of PA2 was observed at critical moisture content of 20%. The dry unit weight increased beyond critical moisture due to the contravention of the surface tension force. The maximum dry unit weight was obtained at slightly higher moisture content in the vibration test. The maximum dry unit weight of coal ash was found to be less than that of the natural soils. It was partly due to a low specific gravity and a high air void content. Similar to the observations of Raymond (1961) and Moulton (1978) the air voids percentage in ash (10 to 15%)

Key Note

was greater than the natural soils (1 to 5%) at the maximum dry density in the proctor test. The maximum dry unit weight by proctor test was obtained at significantly high moisture content (30 to 40%). The maximum dry unit weight by the vibration test was found to be slightly higher (~ 4%) than the proctor test. High optimum moisture content (OMC) is normally because of porous structure of particles.

In field compaction of ash, the use of hand operated base plate compactor had been reported near foundation walls (where rollers could not be used) (Leonards and Bailey 1982). The use of heavy weight vibrators with low frequency is suggested for gravel. One of reasons for selection of high frequency, low weight, and base plate compactor in the present study was as sited above. Moreover, any surcharge was found to reduce amount of densification in case of ash compacted at constant moisture content (Chae and Snyder 1977).

A plate compactor of 220 N and a plate size of 152-mm x 390-mm were selected for vibratory compaction. Vibration was induced on loose left of 150 to 200 mm. The time of vibration required was settled after several trials. It was found that less than 5 seconds and three passes are required at a frequency of 49.166 cps. This produced satisfactory results of density at selected moisture contents. The moisture content density data obtained by core cutters at several locations and depth on test area is plotted along with the data of laboratory vibration test. As ash becomes airborne by slight vibration in dry state and remains suspended in air for long. Therefore, compaction below 5% of moisture content could not succeed.

A CRITERION FOR COLLAPSE

It is recognized that a granular material follows a closer packing under a favorable condition of pressure and moisture (Trivedi & Sud, 2004). Fig.5 (a b c d) shows the concept of collapse for ash material. This tendency may be quantified in terms of the contact separation parameter (D50/Da) defined in the Fig.5(c) and distance of placement void ratio to the minimum void ratio. It is supposed that minimum void ratio occurs in proctor compaction. Therefore a collapse potential (Cp ) and collapsibility factor (F) are defined as,

Cp = Δh/h (1a) F= (ei - emin)/ emin (1b) where, Δh is change in the sample thickness (h) upon inundation. Alternatively, ei is placement void ratio of granular materials and emin is void ratio corresponding to maximum dry density in proctor compaction. Mura et al. (1997) and Trivedi and Sud (2002) empirically related the variation of maximum and minimum void ratio of sand and ashes with the grain sizes and its destitution. The void ratio extent defined by a difference of maximum and minimum void ratio drops by the increasing grain sizes. It implied that the collapsibility increased by decreasing sizes. Therefore larger the value of F, granular materials is more predisposed to collapse. Fig.5 (b c) shows a reduction in collapsibility factor F, with mean size in the loosest and the compacted states. In the loosest state when grains are in progressive contact, a=0.2 and b=0.5

F = a(D50/Da) –b (2)

On compaction the negative exponent ‘b’ of grain separation parameter goes on reducing from 0.5 to one.

Key Note

However, compared to the loosest state, all the granular materials reach nearly a common collapsibility level in a compacted state. At 90% degree of compaction a collapsibility level is arrived, which is associated with small volume change on collapse that does not reflect collapse. Moreover, it has practical problem of precise measurement of the volume change. Thus, the variations in the measured collapse at 90% degree of compaction may forbid interpretation of any trend.

The collapsibility factor allows for assessment of the probable collapse. The probable collapse is assumed to occur if the sample attains a minimum void ratio on inundation. The maximum probable collapse potential is computed by,

Cpr = (ei-emin)/ (1+ei) (3)

where, Cpr is the maximum probable collapse potential, ei is void ratio in a loose state and emin is void ratio corresponding to a maximum dry density in proctor compaction. The probable and the observed collapse potential shows that the decreasing mean size tend to reduce the difference between the maximum probable and the observed collapse at 80% degree of compaction. While at 90% degree of compaction a significant scatter of the data is observed.

As a result of the above observations the classification of granular materials at 80% degree of compaction was found to be appropriate for the evaluation of collapse. The mean particle size was seen to control the collapse of granular materials. If the mean size was greater than 1-mm the granular materials were non-collapsible and others were collapsible under specific conditions. The value of collapse potential in the critical range of stress and moisture was 3 to 6 times that of the corresponding dry condition (Fig.5b). It suggested susceptibility of a non-collapsible dry granular material to the collapse in partly saturated condition. In order to obtain the value of collapse potential of partly wet granular materials, a multiplier may be applied.

Fig.4- Proctor compaction of selected ashes

Fig.5 (a) Effect of grain sizes on collapse potential (Trivedi, 1999)

Key Note

Fig.5 (b) Effect of moisture content on collapse potential (Trivedi et al., 2009)

The collapsible granular materials were further divided into the granular materials of low, medium and high collapsibility on the basis of their collapse potential. The collapsible and the non-collapsible granular materials were identified using the model plate load collapse test on selected samples. Normally, the weight of a particle of a natural soil of similar grain size is 1.5 to 1.3 times that of ash materials. These soils remain stable at or less than 1% volume change (Cp = 0.01). Being light in weight, the ash material has a propensity to be unstable in the presence of buoyancy which plays a role in the model and the field conditions. Therefore, among the light weight granular materials particles 0.75% volume change (Cp = 0.0075) triggered collapse failure in the field. Coincidentally, 1% volume change of soils is 1.3 times that of the limit recognized for the collapsible ash materials.

Fig. 5(c) Definition of contact separation parameter D50/Da (Trivedi et al., 2009)

Fig.5 (d) Criteria of collapse based on collapsibility factor (Trivedi & Sud, 2004)

Key Note

It was observed that the sand and the coarse ash had very close value of the median size. It being a granular material collected dry; having around 25% particles in silt range, had a higher collapse potential than the sand. It was recognized that all the collapsible granular materials had relatively more fines. Among coarse grained granular materials a scatter in collapse potential was observed. A relationship between corrected collapse potential at 200kPa (Dc=80%) and mean particle size is obtained with a satisfactory coefficient of determination. The collapse potential is expressed by, Cp = n (D50/Da)m (4) where Cp is collapse potential of a granular material, D50 is mean particle size in mm, and Da is reference size = 1mm, m and n are fitting constants for the granular materials.

ASH AS A STRUCTURAL FILL

There is only scanty data available on the interpretation of load bearing behavior of ash fills. The penetration test results analyzed by Cousens and Stewart (2003) and Trivedi and Singh (2004a) showed scope for development of new correlations for evaluation of foundation settlements on coal ash. Leonards and Bailey (1982) favored the use of plate load test results for coal ash. Trivedi and Sud (2005, 2007) examined the evaluation of bearing capacity and settlement of ash fills. The present work reviews the plate settlement on coal ash to work out a strategy for evaluation of foundation settlement.

A CONTROLLED TEST SETUP

The ash was deposited in loose lift of 150 mm in a trench of plan dimension of 1.5 m x 1.5 m. It was compacted by a pre-calibrated plate vibrator mounted on a flat rectangular plate (152 mm x 390 mm). The rating of the plate vibrator was 2950 rpm. A constant magnitude of vibration was required to achieve the desired relative density. The trench was filled up in layers maintaining constant density throughout. The density checks were applied at regular intervals using thin core cutter sampling and penetration of an 11 mm diameter needle penetrometer under a constant pressure.

On compacted ash fill, the plate load test was initiated. Few model tests were carried out on surface footings (0.1, and 0.125m wide strip and 0.3m squares) in dry as well as submerged conditions for two different ashes and a sand to check the reproducibility of the results. Additionally on site density checks and laboratory shear tests were also carried out. The displacement of the plate was monitored using pre-calibrated settlement gauges of least count 0.01 mm. The total assembly including hydraulic jack, proving ring and the plate was aligned with the help of a plumb bob to attain verticality.

COMMENTS ON TESTING TECHNIQUE

The load capacity of ash fill was estimated by conducting load tests using different plates on ashes (namely A1 and A2) on varying degree of compaction. A summary of the experimental program is given in Table (6). An average of at least two tests was considered to reach a common load settlement plot if the values were within the range of 10%. The results evaluated from a typical pressure settlement plots are shown in Fig 6(a).

A plate of desired size was placed on the ash fill. A leveled 10-mm thick layer of dry ash was spread on compacted ash to ensure relatively complete and uniform contact between bearing plate and compacted ash. Plate was loaded with hydraulic jack against a reaction truss. After application

Key Note

of seating load, the load was increased in regular increments. Bearing plate settlement was measured with an accuracy of 0.01mm.

0

400

800

1200

0 1 2 3 4 5

Nγ

Ir

At peak by settlement ratio of 20%At peak by double tangentExperimental at settlement ratio of 20%Experimental by double tangentAt constant volume

Fig.6 (a)-Bearing capacity factor for coal ashes (Trivedi & Sud, 2005)

Fig.6 (b)-Progressive failure index and relative dilatancy for coal ashes (Trivedi & Sud, 2005)

Table 6- Summary of load tests

Ash type Test conditions Size (m) Shape Dc(%) Max.

Pressure Sand Dry of Critical 0.1 to 0.9 Strip, square variable Failure A1 A2 Wet of Critical 0.1 to 0.9 Strip, square variable Failure

Each load increment was maintained on the bearing plate as long as no change in the settlement was observed for two hours in succession. Maximums load required for failure of the deposit were estimated by the bearing capacity factors obtained from small-scale tests. A sharp increase of bearing plate settlement was considered as an indication of beginning of the ash failure phase. The settlement observation under final load was taken to the maximum of 24 hours.

BEARING CAPACITY OF ASH FILL

The ultimate bearing capacity of the surface footing on ash fills is proposed to be estimated by

qult = 0.5 Nγ γ' B (5)

B is the width of the footing and γ' is effective unit weight of the footing. The value of bearing capacity factor Nγ (Fig. 6a) is estimated (Trivedi and Sud, 2005) by,

Nγ = η e ζ Ir (6)

Key Note

The realistic estimates of the reference parameter η shall be up such that it takes a base value of Nγ. The typical value of ζ =0.5 to 1. The values of both η and ζ depend upon progressive failure Ipr (Fig. 6b) obtained from relative dilatancy. Bolton proposed the empirical equation to obtain relative dilatancy Ir as,

φpeak = φcr + A Ir (7)

φpeak and φcr are peak and constant volume angle of internal friction. A=5 and 3 for plain strain and triaxial conditions respectively.

)ln()/A (- p pRdrRDQ c ′+−′= φφ (8)

Where Q=10 for sand and 7.7 for coal ash. Rd is relative density and p' is effective mean confining pressure below the footing.

SETTLEMENT OF TEST PLATES ON ASH FILL

Trivedi & Sud (2007) presented the evaluation of settlement of ash fills. In order to investigate settlement characteristics of compacted coal ash, field plate load tests were analyzed for ash compacted to varying degree of compaction and plate sizes.

It is observed that ash may be compacted to same degree of compaction at two moisture contents one dry of the critical and other wet of the critical moisture content. The critical moisture content is defined as the moisture content or range of moisture content in which vibratory compactive effort becomes ineffective and ash bounces back to a loosest packing corresponding to which dry unit weight of ash is minimum in presence of moisture.

In dry side of critical, ash packing is very sensitive to moisture. Within the limitation of workability in field, different degrees of compaction ware selected (i.e. 85.24 % and 81.55 %). The observations of density moisture relationship in field were found similar to that in laboratory vibration test (Fig. 4). The increasing moisture content from 5 to 10 % decreases degree of compaction from 85.24 to 81.55 %. Further the settlement of 300-mm x 300-mm test plate increases from 3.1 to 4.7 mm at 100 kPa.

The coal ash (PA-2) was compacted at a degree of compaction of 85.24 % on the wet side of critical moisture content. It was observed that settlement of 300-mm x 300-mm plate is far less on wet side of critical. Settlement of 300x300 mm square plate at a constant degree of compaction (85.24 %) on dry side of critical (3.1 mm) is almost double of the settlement at wet side of critical (1.45 mm) at constant stress intensity of 100 kPa.

The coal ash was compacted to a higher degree of compaction (90.29 %). By increasing degree of compaction from 85.24 to 90.29 % on wet side of critical, settlement reduced from 1.45 mm to 1.05 mm. That is improvement in the degree of compaction by 5 % (from 85.24 to 90.29 %) the settlement is reduced by one third.

Investigations were carried out by conducting field tests on two plate sizes i.e. 300-mm x 300-mm and 600-mm x 600-mm at varying degree of compaction (85.24 and 90.29 %) on the wet side of critical. There was a significant increase in the settlement by increasing plate size at both degree of compaction [Table 7].

Key Note

Fig.6 (c)-Pressure settlement plot interpreted for coal ashes from varied sources

Table 7-Effect of plate size on settlement on wet side of critical (Trivedi & Sud, 2007)

Plate Size (mm) Settlement at 100 kPa in mm Dc = 90% Dc = 85%

300 x 300 1.05 1.45 600 x 600 2.4 3.8 900 x 900 3.1 5.1

COMPARISON OF SETTLEMENT OF TEST PLATES ON ASH FILL

The case studies [Leonards and Bailey, 1982, Toth et al. 1988; Trivedi & Sud, 2005-07] have shown that standard penetration test results might over estimate settlements of ash fill as high as five times that of predicted value by plate load test. While the cone penetration test over estimated settlements as high as three times (Leonards and Bailey, 1982). The plate load tests tend to give more precise indication of actual settlements of larger sizes. The observed data of several investigators [Leonards and Bailey, 1982, Toth et al. 1988;] is given along with the results of present investigation in Table 4.

From the analysis of data of the present investigation and that published by Leonards and Bailey (1982), it is understood that well compacted ash for the footing size and stress level of interest, has settlement directly proportional to pressure up to 200kPa. Therefore the settlements at 100 kPa are interpolated from the data published by Leonards and Bailey (1982), Toth et al. (1988) and Trivedi & Sud (2005-07) (Table 4).

Critical moisture content is defined as moisture content at which ash attains minimum density when compacted by vibration. The moisture-density curve is almost symmetrical about this moisture content. Therefore, ash may be compacted at two different moisture contents one dry of critical and other wet of critical.

Adding moisture beyond this critical moisture content, apparent cohesion develops which impedes the deformability of ash. This apparent cohesion is destroyed gradually by addition of water beyond optimum moisture. It seems that owing to the development of apparent cohesion ash become for less deformable above at a constant dry density (Dc = 85.24 %). The settlement record at 100 kPa suggest that, on the dry side of critical, settlement is more than two times that of the wet side of critical. The percentage increase in settlement by compacting ash at dry side of critical, instead of wet side of critical at 100 kPa on 0.3m x 0.3m square plate at Dc of 85.24 % is 113.79

Key Note

)

%. There is a significant impact of degree of compaction on dry side of the critical. For a drop in the degree of compaction from 85.24 to 81.55 % (% decrease in degree of compaction 4.32 %) there is increase of settlement at 100 kPa from 3.1 to 4.7 mm (percentage increase in settlement is 51.61 %). Similarly on the wet side of critical, for a decrease in the degree of compaction from 90.29 to 85.24 % (percentage decrease in degree of compaction 5.59 %) there is increase in settlement from 1.05 to 1.45 mm (percentage increase in settlement is 38.09 %). The scale effects are clearly visible in the settlement of ash deposits. Plots are drawn from experimentally observed and predicted settlement for 0.3m x 0.3m, 0.6m x 0.6m and 0.9m x 0.9m square size plates respectively. Using settlement of 0.3m x 0.3m plate as plate settlement, settlement of footing is estimated by the formula (Terzaghi and Peck, 1948):

Sf = Sp ( )(

2

3.03.0

⎥⎥⎦

⎤

⎢⎢⎣

⎡

+

+

fP

Pf

BBBB

(9)

Bp = Width of plate in meter, Bf = Width of footing in meter, Sp = Settlement of plate in mm, Sf = Settlement of footing in mm.

SETTLEMENT PREDICTION OF FOOTINGS ON ASH DEPOSIT

The predicted settlements according to Terzaghi and Peck extrapolation is not in agreement of settlement of footings larger than 0.6m (least dimension) on compacted ash fill (Fig.7a). The predicted settlements based on actual settlement of 300-mm square plate seriously underestimate the observed settlements (D′Appolonia et. al., 1968).

The mean value of ratio of predicted settlement according to Terzaghi and Peck extrapolation and experimentally observed settlements was found to be 0.3. Table 9 presents percentage underestimation of (0.6m x 0.6m) footing settlement by Terzaghi & Peck formula at varying degree of compaction. The predicted settlements according to the criterion suggested by D′Appolonia et al., (1968) are estimated at 100 and 200 kPa. The experimental data for varying size of footing at probable degree of compaction is plotted in Fig. 7a. The expected settlement, at a pressure of 100 kPa, indicates least possibility of exceeding the allowable limit of settlements in the probable degree of compaction (Table 10).

Table 8-Predicted settlements in mm at various degree of compaction as per Terzaghi and Peck

formula (Trivedi & Sud, 2007) Bf (m) Dc = 85.26% Dc = 90.29% Dc < 95% Dc =

98.2% 1.2 3.71 2.68 1.79 1.15 1.5 4.01 2.90 1.94 1.24 1.8 4.25 3.07 2.05 1.31 2.1 4.43 3.21 2.14 1.37

Table 9-Percentage underestimation of footing settlement by Terzaghi & Peck formula at varying

degree of compaction Dc (%) % Under estimation of settlement Interpreted from the data of 98.2 44.36 Toth et. al., 1988 < 95 7.46 Leonards and Bailey, 1082 90.29 56.25 Trivedi and Sud, 2007

Key Note

Table 10-Predicted settlements according to modified criteria

Degree of Compaction Dc (%)

Settlement (in mm) at 100 kPa 3m wide footing.

Interpreted from data of

85.24 9.3 Trivedi and Sud, 2007 90.29 5.6 Trivedi and Sud, 2007 98.20 3.7 Toth et.al., 1988

Fig.7 (a)- Predicted settlements as per Terzaghi and Peck criteria and observed settlement(Table 8) at varying degree of compaction and footing width (Trivedi and Sud, 2007)

Fig.7(b)- Predicted settlements for 1m wide footing at 100 kPa as per SPT

The settlement estimate corresponding to the PLT values obtained for the ash fills is estimated

for 1m wide footing as per Terzaghi and Peck method is shown in Fig. 7(a) which shows excessive rigidity of ash fills to settlement in partly saturated condition. The settlement estimate corresponding to the SPT values obtained for the ash fills is estimated for 1m wide footing at 100 kPa as per Meyerhof (1956) and Burland and Burbage (1984) method (referred as Mh and B&B respectively) in Fig. 7(b) which shows excessive vulnerability of ash fills to settlement in saturated condition. The settlement estimate corresponding to the CPT values obtained for the ash fills is

Key Note

estimated for 1m wide footing at 100 kPa (Fig. 7b) which shows comparison of ash fills to settlement with PLT.

The cyclic mobility-liquefaction characteristics of ash fill (obtained from the same source) in vibration table studies was evaluated by Trivedi et al. (1999) and compared to clean sand. The ash fill settled nearly twice more than sand for the equal volume contained in the vibration chamber (1x0.6x0.6 m3) for nearly half of the dynamic disturbance (Fig. 8). Further tests are recommended to verify predicted settlements of large size footings on dynamic loads.

Fig. 7 (c)-Settlement plot for coal ashes (Trivedi and Singh, 2004a)

Fig.8- Settlements due to dynamic load in vibration table studies (Trivedi et al. 1999)

CONCLUSIONS

The analysis of ash fill is conducted to ascertain whether or not foundation can fulfill their intended function from structural and utilization point of view.

The bearing capacity and settlement of footing on ash compacted on dry side of critical is relatively higher compared to that degree of compaction at wet side of critical. The extent of progressive failure below the footings at varied degree of compaction can be estimated from the relative dilatancy considerations. The settlement of footings may be worked as per PLT, SPT and CPT at the desired degree of compaction and intended footing size and desired stress level for the ash compacted on the wet side of the critical. The pressure corresponding to safe settlement may also be ascertained from the available data.

Key Note

From the estimates of safe loads and safe settlements, allowable bearing pressure may be worked out. Submergence of finer ash deposit is critical to its stability against collapse and liquefaction hence effects of water on ash fill (finer than 75μ) need to be controlled.

ACKNOWLEDGEMENTS

The present study is largely based upon the selected sections of the doctoral thesis work by the author at TIET (Now Thapar University) Patiala under the guidance Prof.V.K.Sud and subsequent work, publications by the author along with several co-authors. The author is thankful to Prof.V.K.Sud, Prof. Sunder Singh and numerous co-workers in development of useful insight in engineering behavior of coal ash. The author thankfully acknowledges the constant encouragements received from Prof. A. Sridharan, Prof. Emeritus, IISc, Banglore. References

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255

INNOVATIVE CONTRACTING FOR SPEEDY CONSTRUCTION

S. Unnikrishna Pillai, FASCE Principal (Retd.), Regional Engineering College (NIT), Calicut, Kerala, India

INTRODUCTION

Time over-runs are very common in construction projects in India. Delays lead to cost escalation, inefficient resource allocation, hardship to the public due to lost services of the facility and overall loss to the economy. There could be many causes for delays in the planning, design and construction stages of a project. This discussion is limited to the construction phase only and introduces some novel contracting methods successfully followed elsewhere to reduce construction time. One of these methods, the incentive-based contracting, which has produced amazing results in several emergency construction projects in the US, is presented in some detail. The essential requirements for the success of such a contract are also considered.

A review of many successful accelerated construction practices used in the US is presented in the ‘Scan Team Report’ of National Cooperative Highway Research Program (NCHRP) Project 20-68A, Scan 07-02 entitled “Best Practices in Accelerated Construction Techniques”1.

INNOVATIVE CONTRACTING METHODS

Conventional contracting method may not yield the desired results in projects requiring speedy time-bound project delivery. The search for measures to accelerate construction has lead to, amongst other options, innovations in the contracting approach. The more commonly used contracting methods in this category are:

1. Design-Build (DB) contracting, 2. Cost + Time (A+B) contracting and 3. Incentive/Disincentive (I/Ds) based and time-limited contracting.

There can also be combinations of these approaches. For example, both DB and Cost + Time methods can include incentive/disincentive elements. All these methods recognize that with proper incentives and work environment, contractors will take up the challenge of speeding up project delivery.

• Design-Build Contracting

Under this method, the basic needs are defined by the owner and the contractor is allowed to develop solutions. Thus the project owner/contracting agency specifies the requirements, expectations and performance quality criteria and awards a single contract to an organization for both architectural/ engineering services and construction. This one organization has the primary responsibility for both design and construction of the project. This Design-Build entity may be a single firm, consortium, joint venture or such other organization.

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This method has several advantages. For the contracting agency, it provides a single point of responsibility/accountability and eliminates the need for coordination between separate design and construction teams. It allows the contractor to optimally choose from alternative materials, techniques and equipment, provided the owner requirements are met. With the designer and contractor working as one team, design and construction activities can proceed concurrently and scheduling considerations can be addressed early on and more effectively, leading to time savings. The use of Design-Build contracting also facilitates the introduction of innovations in design and construction techniques utilizing the separate strengths of designers and builders. The freedom and flexibility the contractor has in the choice of techniques and materials is a major contributor for the success of this method.

Variations of the Design-Build method of contracting have been used in India, mostly in the private sector.

• Cost plus Time Bidding

In this method, the contractor quotes a financial cost together with an associated time it requires for completing the project. Under this scheme, time required is also a biddable commodity and the competition is on “Cost + time”. The comparative evaluation of different bids having different cost-time combinations is more complex. To the writer’s knowledge, this method of contracting is not generally used in India.

• Incentives/Disincentives

The third approach, viz. incentive-based (I/Ds) contracting has been extensively used of late in the US. It has several exceptional successes and appears to be a viable option for India in special cases. This approach is presented in some detail below.

INCENTIVE BASED TIME-BOUND CONTRACTING

In this method, incentives are provided in the contract for delivering the project before a specified date. In addition, a penalty may be imposed for delays. The incentives should be attractive enough to encourage the contractor to expend the necessary effort and resources to reduce construction time. The contract may also include “warranties” for quality of construction. Here, contractors are held accountable for the long-term quality of construction and penalties can be imposed for deficiencies that arise well after construction is complete.

Studies1 of completed projects have shown that the primary factors leading to the success of this method is the active partnership and collaboration between project management team and the contractor, and a supportive design/design process. Although equally effective in planned construction, this method is particularly suited for emergency construction.

Whereas experience in other countries show significant time and cost savings to the owner by adopting the time-limited incentive-based contracting, it has seldom been adopted in India. The working of this method of contracting and the critical requirements for its success are presented below, together with an example.

EXAMPLE – THE MAZE

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The rebuilding of a section of the collapsed highway overpass at the “MacArthur Maze”, a series of major interchanges east of the San Francisco-Oakland Bay Bridge in California is a good example of how to get construction work done speedily through incentive based contracting.

The “Maze”, as it is known, is a tangle of elevated multi-level highway connector ramps merging five major Interstate Highways: I-80, I-580, I-880, I-980 and 24; providing unhindered transfer between them, connecting Oakland, Berkeley and San Francisco; and is used by more than 280,000 cars each day. At about 3.40 a.m. on April 29, 2007, a tanker truck carrying 8,600 gallons of gasoline crashed and burst into flames at the interchange on the ramp leading from I-80 West to southbound I-880. The flames shot up to over 200 ft reaching temperatures in the range of 850oC to 1000oC and the intense heat generated caused the steel beams holding up the I-580 connector just above to buckle and the bolts holding up the structure to soften. An approximately 160 feet (48.8 m) long section of the upper roadway (I-580), 51 ft (15.5 m) wide, collapsed on to the highway beneath (I- 880 connector) – see Fig. 1. The collapsed portion comprised two spans on both sides of a supporting bent, and the bent cap. The original structure consisted of reinforced concrete deck supported on six steel girders. These girders were in turn supported by column bents with steel cap (steel beam connecting the columns).

The two damaged connector ramps, together used by over 80,000 vehicles daily, had to be closed. By a remarkable feat of construction work, facilitated by I/Ds contracting, the collapsed overpass was rebuilt and full traffic restored in just 26 days. Incidentally, this project was the subject of a half-hour TV Documentary entitled “Amazing: The Rebuilding of the MacArthur Maze.”

Emergency demolition contract was given and work begun on the day of the accident. Within two days of the collapse, the California Department of Transportation (Caltrans) demolished the collapsed section of I-580 and cleared all debris. Through various tests, it was determined that the lower I-880 connector ramp can be repaired. After jacking up and supporting with temporary braces, its warped steel girders (which had sagged 9 inches due to the collapse of the I-580 connector on to it) were straightened using a heat straightening technique and reinforced, the deck repaired and the I-880 connector reopened to traffic after being closed for just 8 days.

Fig 1: MacArthur Maze – Section of I-580 collapsed and fell on I-880 below

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The collapsed 48.8 m gap in the I-580 connector ramp, comprising two spans and the middle bent cap (the bent columns were assessed to be safe) had to be rebuilt. The estimated cost of the work was $5,140,070. In order to get this work completed speedily, an incentive based contracting was resorted to. To motivate the contractor for early completion, the contract was drawn up with an incentive/ disincentive clause, offering a $200,000 per day bonus – with maximum at $5 million – for each day the work was completed ahead of the target completion date set as June 27, and levying a $200,000 per day penalty for each day after the deadline. The bonus money offered was based on what officials estimated the highway closures are costing the State. The offer of incentive attracted contractors with reputation for speedy construction and also created competition. The successful (lowest) bid was $867,075, under 17% of the estimate cost, showing that the contractor was counting on finishing the work early and collecting millions more in incentive payments. (Other bids ranged between $1.1 million and $6.5 million.) The bid was opened on May 7, the contract signed at 3.30 p.m. and work started the same evening. While rebuilding, the highway I-880 connector below was kept open (except for 9 days, that too during night only).

The I-580 reconstruction was completed in just 26 days as against the 51 days allowed and the highway opened to traffic on May 25th (see Fig. 2 and Table 1). Against its very low quote of $867,075, the job is estimated to have cost the contracting firm $2.5 million; however they also earned the bonus of $5 million bringing the total payment to the contractor to $5,867,075.

Fig 2: The rebuilt I-580

KEY REQUIREMENTS FOR SUCCESS

Just resorting to an incentive-based contract by itself will not lead to successful early completion of a project. For success, it is imperative that the required environment and support for speedy construction and avoidance of delays are provided through detailed and dynamic planning and effective partnership amongst all associated constituents – the owner/contracting agency,

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designers, reviewers/regulators, contractors and their workers/subcontractors. Some of the key elements essential for the success of this method of contracting are discussed below, also indicating how they were achieved in the Maze project.

• Detailed Planning

Accelerated construction projects require much more detailed initial planning. Detailed execution planning that includes material suppliers, fabricators, and construction equipment suppliers is critical. There must be contingency plans to overcome potential delays due to unexpected events and the plan must be updated regularly. Clear performance criteria for contractor timelines and quality are needed. The contractors also have to develop their construction plans and scheduling in much greater detail because of the time constraints and greater risk.

In the case of The Maze, meticulous planning and preparations began the very day of the accident, including assembly of the project team and search for materials, as the timeline of critical events given in Table-1 demonstrates.

The speed with which the contractor was at the site, within hours of the award of contract, shows the planning the contractor did even before the contract finalization.

Table 1: Timeline of major events1

Date Event Day Const.

Day 29 Apr. 2007 3:41 a.m.: Accident occurs. Demolition contract awarded and

work begins. Initiates search for steel availability and fabrication capabilities

1

30 Apr. 2007 I-880 bridge shored up; Team for I-580 replacement work meets, design work begins

2

1 May 2007 Collapsed portion demolished and debris removed 3 3 May 2007 I-580 contract advertised 5 5 May 2007 I-880 deck repaired; On-site bid conference for I-580 7 6 May 2007 I-880 girders heat straightened, adjacent bent caps repaired 8 7 May 2007 4:30 a.m.: I-880 reopens; 10 a.m.: I-580 bridge bid opens; 3:30

p.m.: I-580 bridge bid awarded; contractor on site within hours; Precast concrete bent cap fabrication started

9 0

8 May 2007 First workday 10 1 11 May 2007 Girder fabrication begins 13 4 15 May 2007 The 244,000-pound, 55' Precast bent cap arrived at night, erected 17 8 17 May 2007 I-880 closed from 8 p.m. Thursday to 5 a.m. Friday to install steel

girders 19 10

19 May 2007 I-880 closed from 8 p.m. Saturday to 5 a.m. Sunday to install last four steel girders

21 12

20 May 2007 Concrete for deck placed from 4 p.m. to7:30 p.m. 22 13 24 May 2007 8:40 p.m.: I-580 opens to traffic, 96 hours after concrete

placement 26 17

25 May 2007 Opened to traffic 27 21 June 2007 Project accepted

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• Design Considerations

Materials and Equipment availability, fabrication time, and handling & transportation difficulties are critical factors for speedy construction. Fabrication can begin right away if the design is based on readily available materials. Designers must consider these when selecting a design approach. Construction speed is enhanced when the design allows repetitive activities. A supportive design/design process can quickly work through issues. Another important element is flexibility in design approach. As the project advances changes may become necessary and the design must be such that it can easily accommodate them.

In the example cited, on the day of the accident itself, Caltrans embarked on a worldwide search on steel availability and fabrication capabilities and the information, gathered within two days, was critical in selecting design and construction alternatives. The swift procurement of steel helped reduce the construction time. An example of flexibility built into the design itself to save time was the bent cap beam design. It could be made of steel as originally built or of concrete, and each has its own advantages/drawbacks. To avoid possible delays to the contractor due to the wrong choice, the designers prepared bent cap designs of both precast post-tensioned concrete, and steel and left the choice to the would-be contractor.

• The Contractor

The contractor must have the technical capability, the ability to mobilize the necessary people and equipment rapidly and the financial capacity and established trust with suppliers and fabricators. The experience and track record of the contractor are very critical. Accelerated construction requires good coordination between activities to eliminate waiting time during activity transitions. Ability to mobilize team effort amongst its own employees and with sub-contractors, by measures such as profit sharing is also important. Generally in such projects the contract will be open only to proven and experienced contractors who are prequalified and invited to bid.

The successful contractor in the Maze project had significant experience with similar emergency reconstruction projects in California (in another project in 1994, the same contractor had earned a bonus of $15.4 million on a $14.7 million contract, completing the work 74 days ahead of schedule). The contractor also agreed to share the profits with its workers and steel fabricator as incentive to work around the clock.

• Incentive

The financial incentives should be attractive to motivate contractors and promote competition. Competent and confident contractors will quote well below estimate costs, banking on completing the project well before the deadline and collecting the incentive bonus. This leads to overall reduction of cost. The pay out of incentive is often more than compensated by the economic benefits accruing from early completion. Management needs to consider the “total project costs” including societal costs rather than “construction cost” only.

The collapse of the Maze structures was estimated to have a negative economic impact to the Bay Area of $6 million a day. That meant opening the freeway a day sooner was effectively worth $6 million to the state. In drawing up the contract mode and its terms, the state considered the respective benefits to the state and the contractor from early completion. The emphasis given for

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speedy project completion was conveyed through the choice of incentive-based contracting with a relatively large incentive bonus, up to $5 million – nearly equal to the estimated cost of the project. In the end, the benefit the state got due to completion over a month ahead of time was far greater than the incentive payout. From the contractor’s perspective, without the incentive, its payoff is totally independent of early completion, and there would be no need to accelerate the construction. The incentive-based contracting system has resulted in victory for all the parties – the State, the Contractor and the Public!

• Partnering

People are the prime movers in successfully accelerating a project. Effective partnership and collaboration between all stakeholders, all working as one integrated team focused on project goals, is vital to successfully complete all accelerated construction projects. Partnering enables parties to make decisions and solve issues at the site as quickly as possible and at the lowest possible level. It also reduces claims and often helps reduce costs. In some accelerated projects, partnering is made mandatory and is accomplished with the assistance of a trained partnering facilitator.

Initiatives that can be taken for achieving effective partnering include: • include all stakeholders (designers, subcontractors, etc.) in the partnering process

between project management and contractor; • provide partnering training to project management’s and contractor’s key personnel at

site; • develop clear understanding of each participant’s role, responsibilities and issues; • have agreement amongst team members to resolve issues at site and at the lowest level; • management to delegate powers to appropriate people at the lowest possible level to

make immediate decisions; • have flexibility and willingness to accommodate changes required to deliver a quality

project within the scheduled time frame; • position designers/reviewers/inspectors at work and fabrication sites for on-site reviews,

feedbacks and approvals/decisions; • provide technical expertise at project site or available at all times to make timely

decisions; • facilitate open communication among project stakeholders to promote cooperation and

understanding and create trust; • hold periodic partnering meetings attended by all players • hold partnering meetings when critical issues arise • enhance transparency.

In the Maze project, partnering was expanded to include designers, subcontractors and fabricators. From the day after contract award, Caltrans positioned a senior reviewer at the steel fabricator’s shop full time to provide on the spot guidance, review and feedback. Quality Assurance Inspectors were also regularly present. Senior engineers were put on site on all three shifts. Designers were available at all hours. Necessary approvals were given quickly.

It was a tribute to the excellent partnering in this project that the President of the steel fabricator firm commented1: “Caltrans came in and put good people in our shop. If there were

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any problems, we could go to them and get immediate answers. Usually it takes weeks. It was a breath of fresh air to have a government agency come in and perform like that.”

• Communications

Open speedy communication among members of the project team, and with suppliers and fabricators is critical for maintaining clarity, quick decision making, and rapid grant of approvals. For this, modern methods such as video conferences, E-mails, mobile phones and electronic transmission of documents can be used. E-mails also provide a record of the communications. Where necessary, communication has to be kept up with the public as well and here the media can be a big help.

SUMMARY For projects needing speedy completion, incentive based time-limited contracting is a well proven option. However, success depends on several key factors. The one factor universally acclaimed as perhaps the most critical requirement for all accelerated projects in nearly all case studies is effective partnering between all stakeholders. Other major requirements are designs conforming to readily available materials, continuous onsite technical support, delegation of powers to make quick decisions and a competent contractor experienced with such works. Reference 1 report, prepared with the objective of facilitating information sharing and technology exchange in the area of accelerated construction, presents case studies of several major projects successfully completed, and also gives detailed recommendations. Needless to add, especially in the Indian context, that a corruption-free, honest, open and accountable management is a vital pre-requisite for success in these types of contracting.

ACKNOWLEDGMENT

The material presented here was gathered from news paper reports and other such information available over the internet and also from Ref. 1. The writer wishes to acknowledge these varied sources.

Reference

Brian A. Blanchard, et. al. (Nov. 2009). “Best Practices in Accelerated Construction Techniques”, Scan Team Report, National Cooperative Highway Research Program (NCHRP), Project 20-68A, Scan 07-02.

http://onlinepubs.trb.org/onlinepubs/nchrp/docs/NCHRP20-68A_07-02.pdf

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AN INSIGHT INTO THE GEOTEXTILE - MUNICIPAL SOLID WASTE INTERFACE

CHARACTERISTICS

S. K. Shukla1, A. K. Singh2 and J N Jha3 1Discipline of Civil Engineering, School of Engineering, Edith Cowan University, Joondalup,

Perth, WA 6027, Australia 2Formerly PhD student, Department of Civil Engineering, Indian Institute of Technology, BHU,

Varanasi, 221 005, India 3Department of Civil Engineering, Guru Nanak Dev Engineering College, Ludhiana, India, Email:

jagdanand@gmail.com

Abstract: In the present paper, interface shear resistance of a geotextile with the municipal solid waste (MSW) has been presented based on the study reported earlier. A comparison has been made with the interface shear resistance of the geotextile with the Ganga sand in loose and dense conditions. The results show that the reinforcing mechanisms in both the cases are not the same. The reinforced dried MSW behaves as more stiff ductile material than the unreinforced dried MSW.

INTRODUCTION

In urban areas, there is scarcity of suitable lands for civil engineering structures throughout the .000000000000000000world. Therefore, the people are forced to make structures even on the Municipal Solid Waste (MSW) dumps created by filling low-lying areas (Fig. 1). Without any ground treatment/improvement, it is generally not possible to construct the foundations on such waste fills because of low load-bearing capacity and large settlements (Sowers, 1973; Fang et al., 1977; Rao et al., 1977; Gabr and Valero, 1990). The use of geotextile/geogrid as a reinforcement layer inside the waste fill can be one of the viable construction practices for improved foundations.

Fig. 1: Aged municipal solid waste dump in Varanasi.

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In reinforcement applications of geotextile/geogrid within the reinforced waste fill beds, the understanding of the geotextile-waste interface shear resistance is required because it is one of the important parameters for estimating the deformation and strength of the reinforced waste fill. The interface shear resistance can be determined by direct shear test (Shukla, 2002, 2012; Shukla and Yin, 2006). In fact, the aim of this test was to determine the coefficient of friction between the geotextile and the municipal solid waste.

In the literature, the test results on the geotextile-waste interaction are scarce. The present paper provides some results as presented by Shukla and Singh (2005) that will be useful for designing the reinforced waste fill-beds to be used as foundations.

MATERIALS USED The municipal solid waste samples were collected from the disposal site in Varanasi (Fig. 1).

All the samples were collected from a depth of about 60 cm below the exposed surface of waste dump. The samples retrieved from the field and used in the testing programme were approximately 2 to 5 years old. Figure 2 shows the average composition of the waste samples.

Fig 2: Average composition of the MSW by percent weight of the components (adapted from Shukla and Singh, 2005).

The in-situ water content of MSW was 19.1% based on the sun-dried procedure (temperature = 24 to 30 °C; relative humidity = 90 to 92%). It should be noted that a major component of the MSW is granular products, which consist of mainly decomposed food products, bricks and baked earthenware pieces, cement concrete pieces, stones, etc.

The reinforcing material used was a nonwoven geotextile (Polyfelt TS-50. Table 1 summarizes the properties of the geotextile used as the reinforcement.

The sand sample was collected from the Ganga river. Its grain size properties are as follows: Sand-size fraction = 99.19% Silt-size fraction = 0.81% Cu = 1.60 Cc = 0.98 Group symbol = SP (Poorly graded sand) Dry density

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Loose condition = 13.6 kN/m3 Dense condition = 16.0 kN/m3

Table 1: Basic properties of the geotextile

EXPERIMENTAL PROGRAMME

The direct shear test was conducted to study the shear resistance of the following:

(i) Sun-dried MSW (ii) Oven-dried sand (iii) Geotextile – sun-dried MSW (iv) Geotextile – oven-dried sand

In direct shear test, the shear resistance between the geotextile and the MSW/sand was determined by placing the geotextile and the MSW/sand within a direct shear box, 60 mm square in plan, divided into upper and lower halves. The geotextile specimen was firmly glued to the metal block that was kept in the lower half of the shear box. The MSW/sand was kept in the upper half of the shear box. A constant normal force was applied to the box, and keeping the lower half of the box fixed, the upper half was subjected to a shear force, under a constant rate of deformation (1.25 mm/minute). The shear force was recorded as a function of the horizontal displacement of the upper half of the shear box. The test was performed at a minimum of three different normal compressive stresses (50 kN/m2, 100 kN/m2 and 150 kN/m2).

It should be noted that the dry unit weight of the MSW was 9.5 kN/m3 in the test. The sand was used in the study to compare the observations of geotextile-MSW shear interaction.

TEST RESULTS AND DISCUSSION

Figure 3 shows the shear stresses at failure against normal stresses obtained from the direct shear tests on loose sand, dense sand, and MSW under both reinforced and unreinforced conditions. The shear strength parameters for all the cases are summarized in Table 2. It is observed that in case of loose and dense sands, the angle of shearing resistance is higher for reinforced case. However, in case of reinforced MSW, the angle of shearing resistance is lower than its value for unreinforced MSW. This might be due to the direct contact of smooth polyethylene pieces, present in the MSW, with geotextile. In fact, their contact causes a slip because of very low frictional resistance. It should also be noted that in case of reinforced loose sand and MSW, there is some adhesion; however, in case of reinforced dense sand, there is no such adhesion.

Figure 4 shows a plot of shear stress against shear displacement for unreinforced and reinforced MSW. It is noticed that the reinforced MSW behaves as more stiff ductile material than the unreinforced MSW. It means reinforced MSW resists stresses at strains lower than the strains

Property Unit Geotextile (Polyfelt TS-50)

Mass per unit area g/m2 212 Thickness mm 1.1 Wide width Tensile Strength kN/m 25 Pore Size (O90) mm < 0.075

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developed in unreinforced MSW. However, the reinforced MSW has a lower strength than the strength of the unreinforced MSW.

Table 2: Shear strength parameters

Materials Shear strength parameters

Cohesion/adhesion (kN/m2)

Angle of shearing resistance (°)

MSW Unreinforced 0 42 Reinforced 3 33.4

Loose sand

Unreinforced 0 23.4 Reinforced 6 28.4

Dense sand

Unreinforced 0 33.4 Reinforced 0 38.4

Fig 3: Shear stresses at failure against normal stresses obtained from direct shear tests on loose sand, dense sand, and MSW under both reinforced and unreinforced conditions (adapted from Shukla and Singh, 2005).

Fig 4: Variation of shear stress against shear displacement for unreinforced and reinforced MSW fills (adapted from Shukla and Singh, 2005).

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CONCLUDING REMARKS

Based on the test results and discussion, the following conclusions are drawn: • The angle of interfacial shear resistance of the geotextile with the sun-dried MSW is

lower than the angle of shear resistance of unreinforced MSW. • Cohesion was induced in the sun-dried MSW as a result of geotextile inclusion. • The reinforced MSW behaves as a more stiff ductile material than the unreinforced

MSW.

References

Fang, H.Y., Slutter, R.J. and Koerner, R.M. (1977). Load bearing capacity of compacted waste material. In the Proceedings of the 9th International Conference on Soil Mechanics and Foundation Engineering, Tokyo, pp. 265-278.

Gabr, M.A. and Valero, S.N. (1995). Geotechnical properties of municipal solid waste. Geotechnical Testing Journal, ASTM, Vol. 18, No. 2, pp. 241-251.

Rao, S.K., Moulton, L.K. and Seals, R.K. (1977). Settlement of refuse landfills. In the Proceedings of the Conference on Geotechnical Practice for Disposal of Solid Waste Materials, Ann Arbor, MI, ASCE, New York, pp. 574-598.

Shukla, S.K. (2002). Geosynthetics and their applications. Thomas Telford, London. Shukla, S.K. (2012). Handbook of Geosynthetic Engineering. Second Edition, ICE

Publishing, London. Shukla, S.K. and Singh A.K. (2005). A study of the municipal solid waste – geotextile

interface resistance by direct shear test. Proceedings of the National Conference on Geotechnics in Environmental Protection, Allahabad, India, April 2005, pp. VI-10-12.

Shukla, S.K. and Yin, J.-H. (2006). Fundamentals of Geosynthetic Engineering. Taylor and Francis, London.

Sowers, G.F. (1973). Settlement of waste disposal fills. In the Proceedings of the 8th International Conference on Soil Mechanics and Foundation Engineering, Moscow, pp. 207-210.

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SELECTION OF SUITABLE STRATEGIES FOR REHABILITATION OF FLEXIBLE

PAVEMENTS

Sanjiv Kumar Aggarwal Head, Department of Civil Engineering, PTU Giani Zail Singh Campus, Bathinda

Abstract: The flexible pavements, which have outlived their design period, need to be rehabilitated in such a way so that the costly process of reconstruction may be prolonged or completely avoided. This paper gives an overview of the procedure to be adopted for selecting the suitable rehabilitation strategies for flexible pavements. In doing so, the first requirement is to gather all of the information necessary to conduct an evaluation of the pavement's present condition and its rehabilitation needs. After assessing the current condition of the pavement, the key types of deterioration present and the deficiencies need to be identified that must be addressed by rehabilitation. Then, from amongst a choice of available rehabilitation techniques, select those, which are best suited to the correction of existing distress and achievement of desired improvements in the structural capacity, functional adequacy, and drainage adequacy of the pavement. Thereafter, individual rehabilitation techniques may be combined into one or more rehabilitation strategy alternatives, and the performance and costs of each may be estimated. Compare the monetary costs and benefits of the different rehabilitation strategy alternatives over a common analysis period, and finally, select the best pavement rehabilitation strategy from amongst the various alternatives considered.

INTRODUCTION

Pavement rehabilitation may be defined as a structural or functional enhancement of a pavement, which produces a substantial extension in service life, by substantially improving pavement condition and ride quality. Pavement maintenance activities, on the other hand, are those treatments that preserve pavement condition, safety, and ride quality, and therefore aid a pavement in achieving its design life. Individual rehabilitation treatments may be categorized as belonging to one of the “4 R’s” – restoration, resurfacing, recycling, or reconstruction. The 4 R’s are good descriptors of the type of rehabilitation effort most appropriate at a given point in a pavement’s life.

• Restoration

It is a set of one or more activities that repair existing distress and significantly increase the serviceability, and therefore, the remaining service life of the pavement, without substantially increasing the structural capacity of the pavement.

• Resurfacing

It may be either of the following:

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(a) Structural overlay, which significantly extends the remaining service life by increasing the structural capacity and serviceability of the pavement, usually in combination with pre-overlay repair and recycling. A structural overlay also corrects any functional deficiencies present.

(b) Functional overlay, which significantly extends the service life by correcting functional

deficiencies, but which does not significantly increase the structural capacity of the pavement.

• Recycling

It is the process of removing pavement materials for reuse in resurfacing or reconstructing a pavement or constructing some other pavement. For flexible pavements, this process may range from in-place recycling of the surface layer, to recycling material from all pavement layers through a hot mix plant.

• Reconstruction

It is the removal and replacement of all bituminous layers, and often the base and sub-base layers, in combination with remediation of the subgrade and drainage, and possible geometric changes. Due to its high cost, reconstruction is rarely done solely on the basis of pavement condition. Other circumstances, such as obsolete geometrics, capacity improvement needs, and alignment changes, are often involved in the decision to reconstruct a pavement.

REHABILITATION STRATEGY SELECTION PROCESS

It should typically consist of the following principal activities:

(i) Data collection: Gathering all of the information necessary to conduct an evaluation of the pavement's present condition and its rehabilitation needs.

(ii) Pavement evaluation: Assessing the current condition of the pavement, identifying the key types of deterioration present, identifying deficiencies that must be addressed by rehabilitation, and identifying uniform sections for rehabilitation and design over the pavement section length.

(iii) Selection of rehabilitation techniques: Identifying candidate rehabilitation techniques, which are best suited to the correction of existing distress and achievement of desired improvements in the structural capacity, functional adequacy, and drainage adequacy of the pavement.

(iv) Formation of rehabilitation strategies: Combining individual rehabilitation techniques into one or more rehabilitation strategy alternatives, developed in sufficient detail so that the performance and costs of each may be confidently estimated.

(v) Life-cycle cost analysis: Comparing the monetary costs and benefits of the different rehabilitation strategy alternatives over a common analysis period.

(vi) Selection of rehabilitation strategy: Considering monetary factors and non-monetary factors together in selecting one pavement rehabilitation strategy from among the alternatives considered.

DATA COLLECTION

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The purpose of data collection is to gather all of the information necessary to conduct an evaluation of the pavement’s present condition and rehabilitation needs, develop one or more rehabilitation strategies, predict the performance of each strategy, and estimate the cost of each strategy.

• Pavement Section Identification

This involves identifying the location of the pavement section by road name or number, direction, district, nearby city or town, kilometer stone limits, i.e. all information that will be needed to locate the pavement section and estimate rehabilitation costs over its length. Information such as the locations of bridges, underpasses, and flyovers, etc., should also be noted.

• Pavement Section Inventory

This involves examining pavement management files, construction records, and reports from past evaluation and rehabilitation activities for the purpose of determining the pavement type, pavement age, pavement layer materials and thicknesses, number of lanes, widths of lanes and shoulders, predominant subgrade soil type, and sub-drainage features. Traffic Analysis - The current traffic volumes and axle loadings and anticipated traffic growth rates should be determined. With this information, traffic volumes and axle loadings may be forecasted for the design traffic lane (usually the outer lane in one direction) over whatever design periods are later selected for the rehabilitation strategy alternatives considered. For the purposes of pavement rehabilitation strategy selection, the current and projected future traffic should be characterized in terms of whatever traffic input is used in the resurfacing and reconstruction design procedures used by the agency.

• Distress Survey

Rehabilitation of a pavement is most likely to provide satisfactory performance and cost-effectiveness, if it is selected on the basis of knowledge of the types of distresses occurring in the pavement and the causes for those distresses, and it effectively repairs those distresses. A good understanding of the types of distress, which may occur in different types of pavements, and the causes for those distresses, is therefore essential to the success of pavement rehabilitation. The different types of distresses, which occur in flexible pavements, are briefly summarized in Table 1.

A field survey is required to accurately determine the types, quantities, severities, and locations of distress present. Each of the distresses present may be indicative of rehabilitation needs and should be recorded by type, severity, and quantity in the distress survey. Automated devices are also available for use in conducting distress surveys. These devices operate at highway speeds without disrupting traffic, and thus are particularly well suited to high traffic volume situations.

• Deflection Testing

Deflection testing is conducted on flexible pavement s for the purposes of back-calculating the stiffnesses of the subgrade and pavement layers, assessing the remaining life of the pavement, and determining the overlay thickness required to satisfy a structural deficiency. Flexible pavements should be tested in the outer wheel path of the outer traffic lane, which is just one to

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two feet from the lane edge, for the purpose of attempting to assess the extent of fatigue damage. The assumption of infinite horizontal layers is thus violated, but this is generally ignored. While some agencies may not be equipped for nondestructive deflection testing, such testing is always highly desirable, especially when the distress survey indicates that the pavement requires a structural improvement.

Table 1: Flexible Pavement Distress Types and Causes

Distress Causes Comments

Fatigue cracking, also called alligator cracking

Fatigue damage in the bituminous mix surface or stabilized base

Can progress to potholes, beginning first at locations where the underlying base and subgrade materials are weakest.

Block cracking and thermal cracking

Use of bitumen, which is too stiff for the climate. Bituminous mixes subjected to low traffic volumes may not densify sufficiently and may become brittle, which leads to block cracking.

More often seen in large paved areas, such as parking lots and airport aprons, than on roads and streets, which carry channelised traffic. Bituminous mix may also be excessively brittle if it is mixed too long at the hot mix batch plant, mixed too hot, or stored too long.

Longitudinal cracking

Inadequate compaction at the edges of longitudinal paving lanes, reflection of underlying old pavement edges or cracks in a stabilized base, or application of heavy loads or high tyre pressures in rutted wheel paths.

Longitudinal cracking in rutted wheel paths is more likely when heavy loads or high tyre pressures are applied during cold weather to a rutted pavement with a weak subgrade.

Shoving and corrugation

Shear flow or slippage between layers, due to inadequacies of the bituminous mix.

In an unstable mix, shoving develops first in areas where vehicles move more slowly. Additional horizontal friction forces produced by vehicles braking or accelerating can produce corrugations in an unstable mix.

Bleeding Excess of bitumen or insufficient air voids in the bituminous mix.

Bleeding occurs in hot weather. Bitumen expands and fills the voids in the Bituminous mix, and is then exuded at the pavement surface. This process is not reversible.

Slippage cracking Poor bond between the surface layer and underlying layer.

Slippage cracking occurs in areas where vehicles brake and turn.

Rutting Inadequate bituminous mix design for the applied tyre pressures, or permanent deformation in the base, sub-base, or subgrade.

This is permanent or unrecoverable traffic associated deformation within pavement layers, which, if channelised into wheel paths, accumulates over time and gets manifested as ruts.

Ravelling and weathering

Loss of bond between the aggregate and binder. Ravelling is loss of aggregate particles, weathering is loss of bitumen.

This may be due to insufficient bitumen content, poor adhesion of the bitumen to the aggregate, hardening of the bitumen, or segregation or inadequate compaction of the bituminous mix during construction.

Bumps, heaves, and settlements

Foundation movement (frost heave, swelling soil), localized consolidation

Detract from riding comfort. At high severity may pose a safety hazard.

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• Measurement and Consideration of Temperature

Bituminous mix temperature measurements are required when testing bitumen and bitumen overlaid pavements because the resilient modulus of bituminous mix varies substantially with temperature. It is not uncommon for the bituminous mix temperature to vary by 15ºC or more during a typical day of deflection testing. This magnitude of temperature variation could easily correspond to a variation of 35,000 kg/cm2 in bituminous modulus. Failure to account for this variation will result in incorrect moduli being used for the bitumen layers.

• Coordination of Deflection Testing with Visible Distresses

Flexible pavements with alligator cracking in the wheel paths may show significant variability in deflections and also in the degree of distress along the length of the pavement section. A correlation can usually be observed between the severity of the alligator cracking and the magnitude of the maximum deflection. Assuming that one of the primary purposes of the deflection testing of a flexible pavement is to assess its structural condition, it is useful to test at locations with various degrees of cracking. Even severely alligator-cracked areas can usually be tested.

• Materials Sampling and Testing

Any rehabilitation strategies involving overlay options will require information about the existing pavement materials and subgrade, for purposes of overlay thickness design. Depending on the design procedure used, the information required may include:

• Thicknesses of the pavement layers, • Condition of the pavement layer materials, • Elastic moduli of the pavement layers, and • Elastic modulus or ‘k’ value of the subgrade.

The stiffnesses of the pavement layers and subgrade may be determined from nondestructive deflection testing, as described previously. Layer thicknesses and stiffnesses may also be determined from laboratory testing of materials samples, or in some cases, from field tests.

• Profile and Roughness Measurement

Roughness may be characterized by indices, which are based on either the measured profile of the measured surface, or the output from a roughness meter installed in a vehicle. At the project level, roughness measurements can be useful in locating areas of excessive roughness, deciding whether or not a non-overlay rehabilitation strategy should include some treatment for reducing roughness and assessing the effectiveness of such treatments. The measured profile may also be used to simultaneously produce, by simulation, the outputs of other roughness devices measuring devices as if those devices had been used to measure the surface.

PAVEMENT EVALUATION

The purpose of pavement evaluation is to assess the current condition of the pavement, identify the key types of deterioration present, identify deficiencies that must be addressed by rehabilitation, and identify uniform sections for rehabilitation design and construction over the pavement section

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length. Rehabilitation of a pavement is most likely to be successful, i.e., provide satisfactory performance and cost-effectiveness, if it is selected on the basis of knowledge of the types of distresses occurring in the pavement, and understanding of the causes for those distresses. The principal distresses that occur in flexible pavements, and the mechanisms that cause them, were summarized previously in Table 1. Many distresses have more than one possible cause. It is important to study the distresses observed in the field survey in order to correctly identify the one or more mechanisms causing the distress observed.

• Structural Evaluation

It involves examination of the collected distress, deflection, materials, soils, and drainage information for assessment of the current structural condition of the pavement, that is, how much structural damage has been done to the pavement so far; and assessment of the remaining structural life of the pavement, that is, how many more loadings it can support before failure.

• Functional Evaluation

It involves comparing the pavement’s measured roughness, skid resistance, and rut depth to the agency’s standards for these functional parameters.

• Identification of Uniform Sections

Pavement sections that are uniform with respect to design, geometry, materials, structural capacity, soils, distress, traffic, drainage, etc., should be identified on the basis of the collected inventory, materials, distress, deflection, and other data. The simultaneous consideration of several inventory, distress, and deflection parameters could conceivably result in the division of the pavement section into several short sections.

SELECTION OF REHABILITATION TECHNIQUES

The purpose of rehabilitation technique selection is to identify candidate rehabilitation techniques which are best suited to the correction of existing distress and achievement of desired improvements in the structural capacity, functional adequacy, and drainage adequacy of the pavement. A pavement rehabilitation strategy is a combination of individual rehabilitation treatments. A rehabilitation strategy is explicit enough, in terms of both the types and quantities of treatments to be applied, that it can be evaluated and compared with other rehabilitation strategy alternatives, in terms of expected performance and costs.

• Full-depth or Partial-depth Repair, or Patching

This consists of localized repair of distresses related to structural damage, materials problems, or construction problems. The repair may be full depth down to the subgrade or an intact sub base layer, or partial depth, i.e. bitumen surface only, depending on the nature of the distress. Patching may also be done on a flexible pavement either for maintenance purposes or rehabilitation purposes.

• Cold Milling

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This is the removal of material from a flexible pavement surface, using carbide bits mounted on a rotating drum. Cold milling may be done for one or more of several reasons: to texturize the surface prior to resurfacing in order to enhance bond, to remove excess bituminous thickness, to remove oxidation at the surface, to remove unstable bituminous material, to modify the longitudinal or transverse grade, to remove rutting, and to remove bumps. Infrequently, cold milling is done without subsequent resurfacing, to remove rutting or bumps, and to improve surface friction.

• Hot-in-place Recycling

This is the on-site rejuvenation of aged bituminous material. Hot in-place recycling is usually but not always done in conjunction with resurfacing. Rejuvenating the existing surface prior to placing an overlay enhances bond and discourages reflection cracking. Hot in-place recycling may also be done without a subsequent overlay, to correct surface distresses such as minor corrugations or bleeding. The process involves heating the surface to the desired depth with slow-moving, high-intensity heaters, and virgin bituminous material, and then either compacting the rejuvenated surface, or placing an overlay.

• Cold-in-place Recycling

This is the on-site cold milling of bituminous material, mixing of the material with emulsified bitumen or other additives such as lime, and laying down and re-compacting the material. Cold in-place recycled material is not as stiff or as stable as hot-mix bitumen, so it usually must be capped with an bituminous wearing course or a single or double surface treatment.

• Bituminous Overlay

This may be placed to improve ride quality and surface friction, or may be placed for the purpose of substantially increasing structural capacity. The performance of a bitumen overlay depends primarily on the thickness of the overlay, its bituminous mix design, and the type and extent of pre-overlay repair and surface preparation.

FORMATION OF REHABILITATION STRATEGIES

The purpose of formation of rehabilitation strategies is to combine individual rehabilitation techniques into one or more rehabilitation strategy alternatives, developed in sufficient detail that their performance and costs may confidently estimated. The formation of each rehabilitation strategy alternative should address the following four issues:

• Is a structural improvement needed to correct a structural deficiency • Is a functional improvement needed to correct a functional deficiency • What additional repair techniques are needed • Is a drainage improvement needed to correct a drainage deficiency

Multiple rehabilitation strategy alternatives may be developed by considering more than one structural improvement option, more than one functional improvement option, or more than one feasible combination of repair techniques. Variations on the rehabilitation strategy alternatives may be developed by considering different overlay thickness designs and different quantities of repair.

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• Correct Structural Deficiency

If a structural deficiency exists, each of the rehabilitation strategy alternatives should include one of the following techniques:

1. Bitumen overlay 2. Concrete overlay 3. Reconstruction

• Correct Functional Deficiency

If a functional deficiency exists and is not addressed by a structural improvement, each of the rehabilitation strategy alternatives should include one of the following techniques:

1. Cold milling 2. Hot surface recycling 3. Thin bitumen overlay 4. Ultrathin concrete overlay

• Drainage Deficiency

If a drainage deficiency exists, a drainage improvement option may be considered for inclusion in some or all of the rehabilitation strategy alternatives. Drainage improvement options for in-service pavements may include retrofitting or replacing longitudinal sub-drains and outlets, or day-lighting the base by replacing shoulder base material and repaving the shoulders.

LIFE-CYCLE COST ANALYSIS OF PAVEMENT REHABILITATION STRATEGIES

The objective of life-cycle cost analysis is to evaluate the economic effectiveness of different mutually exclusive investment alternatives over a certain time period and to identify the most cost-effective alternative. The selection of an appropriate rehabilitation strategy for a pavement should consider all of the costs and benefits that will be incurred as a result of the selection of that strategy. These costs and benefits should be estimated over a time frame that is sufficiently long to reflect differences in performance among different strategy alternatives. This period of time is generally referred to as the analysis period. A fair comparison among alternatives over the analysis period requires that their associated costs be expressed in terms of some common monetary measure. The calculation and comparison of the costs and benefits of different alternatives over the analysis period is called life-cycle cost analysis. The period of time for which either a new pavement or a rehabilitation treatment is designed to serve is often called the design period. In the context of rehabilitation strategy selection, it may be more convenient to use the term performance period. For many rehabilitation techniques, the best estimate of the life of the technique must come from field performance observations or empirical models developed from field performance data. Thus, the term performance period encompasses more generally the expected life of any rehabilitation treatment, whether or not it is designed.

CONCLUSION

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Pavement rehabilitation incorporates structural or functional enhancement of a pavement, which produces a substantial extension in service life, by substantially improving pavement, condition and ride quality. The rehabilitation strategy selection procedure, which may be used by various highway agencies, typically consist of the activities, such as the data collection, pavement evaluation, selection of rehabilitation techniques, formation of rehabilitation strategies, life-cycle cost analysis over a common analysis period, and finally, selection of rehabilitation strategy. The rehabilitation strategy, which is ultimately selected, may simply be that which is found to be most cost-effective in the life-cycle cost analysis. However, in many cases, an agency may weigh the cost analysis results with other decision factors that cannot be expressed in monetary terms, for selection of the rehabilitation strategy.

References

AASHTO (1993) “Guide for Design of Pavement Structures”, American Association of State Highway and Transportation Officials, Washington, D. C.

Kathleen T. Hall, Carlos E. Correa, Samuel H. Carpenter and Robert P. Elliot (2001) “Rehabilitation Strategies for Highway Pavements”, National Cooperative Highway Research Program, Transportation Research Board, Washington.

ODOT (1999) “Pavement Design and Rehabilitation Manual”, Ohio Department of Transportation Columbus, Ohio.

Peterson, D., E., (1985) “Life-Cycle Cost Analysis of Pavements”, National Cooperative Highway Research Synthesis No. 122, Transportation Research Board.

Pierce, L. M. and Mahoney, J. P. (1996) “Description of Rehabilitation Process Used in Washington State Pavement Management System”, Transportation Research Record No. 1524.

Sebaaly, P. E., Hand, A., Epps, J., and Bosch, C., (1996) “Nevada’s Approach to Pavement Management,” Transportation Research Record No. 1524.

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RECYCLED AGGREGATES-AN OVERVIEW

Pinal Saini*, Jagbir Singh** and Rajesh Kumar*** * Punjab Technical University, Jalandhar, Punjab

** Department of Civil Engineering, GNDEC, Ludhiana, Punjab, India ***Department of Civil Engineering, PTU GZS Campus, Bathinda, Punjab, India

INTRODUCTION

The protection of the environment is a basic factor, which is directly connected with the survival of the human race. Parameters like environmental consciousness, protection of natural recourses, sustainable development play an important role in modern requirements for construction works. Parallel to rapid economic growth and urbanization in Asia, environmental impacts from construction and demolition (C&D) waste are increasingly becoming a major issue in urban waste management. C&D waste management in developing countries in the Asian region is relatively undeveloped and emerging. The subject of concrete recycling is regarded as very important in the general attempt for sustainable development at present.

Concrete is the premier construction material across the world and the most widely used in all types of civil engineering works, including infrastructure, low and high-rise buildings, defence installations, environment protection and local/domestic developments. Concrete is a manufactured product, essentially consisting of cement, aggregates, water and admixture(s). Among these, aggregates, i.e. inert granular materials such as sand, crushed stone or gravel form the major part around 75 % of the total volume of the concrete. Traditionally aggregates have been readily available at economic prices and of qualities to suit all purposes. However, in recent years the wisdom of our continued wholesale extraction and use of aggregates from natural resources has been questioned at an international level. This is mainly because of the depletion of quality primary aggregates and greater awareness of environmental protection. In light of this, the availability of natural resources to future generations has also been realised.

Previous studies show that approximately 40% of the generated waste portion globally originates from construction and demolition of buildings. In general, Construction and Demolition (C&D) waste is bulky, heavy and is mostly unsuitable for disposal e.g. incineration or composting. This poses a great problem for waste management in urban areas in Asia.

• Environmental Impact of C & D Waste

Reduce, Reuse, and Recycle (“3Rs”) Action Plan and the Progress of Implementation on Science and Technology for Sustainable Development were adopted during the G8 Sea Island Summit in USA in 2004. C&D sector in most of countries know about Reduce, Reuse and Recycle (3R) principles. However, most localities have no policy for reduce, reuse and recycling practices that explicitly address to C&D waste management. National and local governments and authorities in urban areas have attempted to meet the demand for housing and services through increased construction. However, lack of awareness of resource-efficient construction practices has resulted in excessive use of natural resources and generation of large amounts of construction waste that is rarely recycled.

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Components of C&D waste are typically concrete, asphalt, wood, metals, gypsum wallboard, and roofing. In addition, construction industry is one of the major contributors to the environmental impacts, which are typically classified as air pollution, land pollution, noise pollution and water pollution. Open burning of C&D waste at construction sites is practiced in many rural areas as well as in many urban areas. Moreover, aside from open burning, the most common management practice for C&D waste is land filling, where the waste is dumped in municipal solid waste (MSW) landfills, and on illegal dumping sites.

Regarding concrete, which is the most important construction material, the protection of the environment concerns three basic axes:

1. Use of high amounts of raw materials (aggregates for the production of cement and concrete) which result in the decrease of available natural resources which is continuously sub-graded.

2. Consumption of high amounts of energy for the production, transport, use of raw materials and final ones, as cement and concrete.

3. Creation of big volumes of old concrete from old construction works (demolition wastes).

The main reasons for the increase of this volume of demolition concrete waste are:

1. Many old buildings and other structures have overcome their limit of use and need to be demolished; structures,evenadequatetouse,areunderdemolition,becausetherearenewrequirementsandnecessities;

2. Creation of building wastes which result from natural destructive phenomena (earthquakes, storms)

• Current Situation of Construction Waste in Asia

Figure 1illustrates C&D waste generation in million metric tons in Asian countries. PR China has the highest waste generation in Asia, followed by Japan and South Korea. Currently, no data on C&D waste generation at national level for Thailand, but in Bangkok Metropolitan Area (BMA) tremendous amount of C&D waste is observed. Actual statistics of C&D waste generation is illustrated in countries like Hong Kong SAR, India, Japan, South Korea, Singapore, BMA Thailand, Taiwan and Vietnam. Most of the countries in Asia do not have data and information on C&D waste generation. The C&D waste is included in the Municipal waste.

• Indian Scenario

Central Pollution Control Board has estimated current quantum of solid waste generation in India to the tune of 48 million tons per annum out of which, waste from construction industry only accounts for more than 25%.

As illustrated in Figure 1, the amount of construction waste generated in India is less compared with other countries, because India has large geographical area and because the generated waste does not account the amount of renovation and demolition waste. In addition, the

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reason also is that because most of the C&D waste is dumped anywhere e.g. in Pune, India, C&D waste is dumped along the riverside haphazardly (Express India news, 2008).

Fig. 1: C&D Waste Generation in Million Tons (Source: Appendix table on Summary of C&D waste management)

Technology Information, Forecasting and Assessment Council (TIFAC), New Delhi conducted a techno-market survey on ‘Utilization of Waste from Construction Industry’ targeting housing/building and road segment. The total quantum of waste from construction industry was estimated to be 12 to 14.7 million tons per annum out of which 7 to 8 million tons was concrete and brick waste. According to findings of survey, 70% of the respondent gave the reason for not adopting recycling of waste from Construction Industry as “not aware of the recycling techniques” while remaining 30% indicated that they were not even aware of recycling possibilities. Further, the user agencies/ industries pointed out that presently, the BIS and other codal provisions do not provide the specifications for use of recycled product in the construction activities.

RECYCLED AGGREGATES

Recycled aggregates are aggregate resulting from the processing of inorganic material previously used in construction, e.g. crushed concrete, masonry, brick. Recycled aggregates can be broadly subdivided into two main categories:

1. Recycled Concrete Aggregate- RCA derived predominantly from crushed concrete rubbles which contains a maximum of 5% masonry.

2. Recycled Aggregates- RA created from the broad field of construction and demolition waste (C&DW) such as brick-based RA and asphalt-based RA that can contain up to 100% masonry.

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Fig: 2 recycling plant at Hong Kong

Recycling of C&DW can take place either at the site from which the material is sourced using mobile crushers, or the material may be transported to a fixed recycling centre (sometimes referred to as urban quarries) where large stockpiles may be accumulated. In general, recycling plant basically comprises: a primary sorting facility, crushers i.e. primary and secondary, impurity removal facilities (magnetic tools to separate metals, air knives, and manual sorting belts), removal services (heavy duty trucks and tractors), stockpiles, and storage areas ( Fig: 2). Use of recycled aggregate in concrete can be useful for environmental protection and economical terms.

• Comparison of natural aggregates and recycled aggregates

Recycled aggregates look like crushed stone, but differ from those of natural aggregates. RA is more angular have a rougher surface texture than those of natural aggregates. Roughly textured, angular and elongated aggregates require more water to produce workable concrete than smooth, rounded conventional aggregates. The light weight and porous cement mortar attached to the recycled aggregate results in lower specific gravity and higher water absorption than those of same size natural aggregates. Because of the attached cement paste in the RACs, the density of these materials is about 3-10% lower and water absorption is about 3-5 times higher than the corresponding natural aggregates. It is therefore important that density and water absorption of RAC are determined carefully, prior to their use in concrete production. This must be done in order to avoid large variations in properties of hardened concrete as well as in achieving fresh concrete of adequate workability, stability and cohesiveness.

Table 1: Typical physical characteristics of recycled and natural aggregates

Property Coarse aggregates ( 5- 20 mm)

Recycled concrete aggregate

Natural aggregate

Relative density kg/ m3 2580 2540

Loose bulk density kg/ m3 1190 1340

Water absorption, % 5.5 2.5

Attached cement paste, % 10.2 -

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Fig: 3 Comparison between recycled aggregate and natural aggregate

• Advantages of Recycled Aggregate Concrete

In the past, almost all materials which are used in the construction industry were entirely natural and all waste from demolished buildings was disposed of in landfills and partially in unauthorized places. The utilisation of the recycled aggregates created from processing C&DW in new construction has become more important over the last two decades. There are many factors contributing to this, from the availability of new material and the damage caused by the quarrying of NA and the increased disposal costs of waste materials. Due to advances in manufacturing of crushing machinery and recycling processes, it became possible to scale or crush down large masses of C&DW into smaller particles to produce recycled aggregate (RA) at acceptable cost. The advantages of recycling C & DW are numerous:

1. Reduces the amount of C&DW entering landfill sites. 2. Reduces the use of natural resources in construction. 3. Contributes to the environment. 4. Provides a renewable source of construction material. 5. If used in situ, reduces haulage costs

• Uses of Recycled Aggregates

Traditionally, the application of recycled aggregate is used as landfill. Nowadays, the applications of recycled aggregate in construction areas are wide. The applications are different from country to country. Recycled aggregate have been used as concrete kerb and gutter mix in Australia, as granular base course in the road construction and in embankment fill, used as backfill materials in the pipe zone along trenches, used as paving blocks in Hong Kong and also used to produce the masonry sound insulation blocks. Some construction practitioners in Asian countries carry out reduction of C&D materials through the practice of offsite prefabrication units and pre-mix concrete materials; this is common practice to avoid excessive wastage and quality control. Aggregates from recycled concrete (RCA) are already used in all countries in various applications of civil engineering works, as road pavement materials, subbasements, soil stabilization, improvement of sub ground, production of concrete of many categories, etc.

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The use of recycled aggregate concrete (RAC) has been restricted to lower grade applications only due to lack of appropriate specifications and mix proportion guide lines. The use of RCA in construction works is a subject of high priority in building industry throughout the world. Indicatively, 10% of used aggregates in Great Britain are RCA, 78,000 tons of RCA were used in Holland in 1994 as the corresponding national organization admitted that the use of 20% of coarse RCA result in no differentiation of the properties of fresh or hardened concrete. The rapid development in research on the use of RCA for the production of new concrete has also led to the production of concrete of high strength performance. It should be noted, of course, that the use of coarse RCA (up to 30%) is normally recommended but the addition of super plasticisers is often considered necessary for achieving the required workability of new concrete.

CONCLUSIONS

In the present work an introduction to recycled aggregate is given in order to be used as a basis for pilot and long scale works where the use of RCA can be estimated as more economic and friendlier to the environment. Good quality recycled aggregates can be produced with commercial plants that are used for the production of crushed-rock aggregates. Clearly, this information could encourage clients and demolition contractors to direct C & D waste for production of RCA, while reducing disposal to landfill.

The study shows that plain as well as reinforced concrete can be crushed using primary and secondary crushers to provide crushed aggregate with an acceptable quality to current BS 882 requirements. Up to 30% coarse RCA can be used, without any modification in the mix design, in concrete construction with performance similar to natural aggregate concrete.

Overall, the practical benefits resulting from the use of recycled aggregates are not only on environmental and economical fronts, but they could also provide the construction industry with technical information on a marketable product, which is presently under-utilized.

References

Chiu Kwong Man Karen, (2006), The use of recycled concrete aggregate in structural concrete around south east Queensland, B.Tech. Thesis, Faculty of Engineering and Surveying, University of Southern Queensland.

Khaldoun R, (2007), Mechanical properties of concrete with recycled coarse aggregate, Building and Environment journal, 42, 407–415.

Kou Shicong, (2006), Reusing recycled aggregates in structural concrete, Ph. D thesis, The Hong Kong polytechnic university.

Limbachiya M C, Koulouris A, Roberts J J and Fried A N, (2004), performance of recycled aggregate concrete, Kingston University, UK, 127- 136

Limbachiya M C, Leelawat T, Dhir R K.(2000), Use of recycled concrete aggregate in high-strength concrete. Structural materials, 33:574–580.

Ramammurthy K and Gumaste K S, (1998), Properties of recycled aggregate concrete, Indian Concrete Journal, volume 72, N1, 49-53.

Salem Ahmed Abukersh, (2009), High quality recycled aggregate concrete, Ph. D thesis, School of Engineering and the Built environment, Edinburgh Napier University, UK.

Singh S K and Sharma P C, (2007), Use of recycled aggregates in concrete- A Paradigm Shift, National building materials journal.

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EVALUATING LIQUEFACTION BEHAVIOR OF SOLANI SAND

Rajiv Chauhan Department of Civil Engineering, Deen Bandhu Chhotu Ram University of Science and

Technology, Murthal, Sonepat, Haryana, India

Abstract: The damage potential associated with liquefaction is the reason behind geotechnical studies of earthquake –induced liquefaction. Efforts have been made in developing procedures for evaluating the potential for liquefaction during earthquakes thereby either limiting or eliminating damage during liquefaction This paper presents the evaluation of liquefaction behavior of solani river sand experimentally using shake table and cyclic Triaxial apparatus. Tests had been conducted on the shake table at different accelerations varying from 0.1g to 0.3g. For particular acceleration, the densities of the sample were also varied from 35% to 65%. The frequency was kept at 4 Hz. Excess pore pressure ratio was used as a parameter for study of liquefaction behavior. The results were in close arrangement with experiments. It had been found that liquefaction reduces with increase in density of sample.

Keyword: Acceleration, Liquefaction, Relative Density, Shake Table, Cyclic Triaxial, Frequency

INTRODUCTION

Earthquake is a natural phenomenon, which cannot be prevented, but safety measures can be taken to prevent widespread damage to man-made structures. Liquefaction is one of associated phenomenon in saturated sands due to earthquakes. Casagrande and his student Castro started pioneer work on soil liquefaction (Casagrande, 1940; Castro 1969), which was followed by Seed and his fellows at the University of California Berkeley (1966). Seed and Lee (1966) used cyclic triaxial testing with harmonic loading to approximate liquefaction potential and developed procedure to evaluate the liquefaction potential through stress-controlled testing (Seed & Idriss, 1971). The phenomenon and factors of the liquefaction have been studied and developed by Florin and Ivanov (1961), Seed and Idriss (1966), Gupta (1977), Martin et al. (1975), Seed et al. (1976), Prakash (1981), Sitharam et al. (2004), Singh (2009) and several others. It is important to investigate generation and dissipation of the pore water pressure in the sand deposit under the action of dynamic loads. The present research work is aimed at determining experimentally the liquefaction behaviour of sand using shake table test set up and cyclic triaxial test apparatus.

MATERIAL USED IN STUDY

• Sand and its Properties

The sand (classification as SP) collected locally from the bed of river Solani was used in experimental studies. The sand was cleaned and air dried before use. From particle size distribution curve (Fig. 1) coefficient of uniformity was determined as 1.8 and D50 as 0.27. The sand with specific gravity of 2.65 had less than 5% particles passing through IS: 75 micron sieve and showed no cohesion.

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Fig 1: Particle Size Distribution curve

• Test Tank

The test bin is a water tight tank 1060 mm long, 600 mm wide and 600 mm high as shown in Fig.2. The sides of the tank consist of rigid mild steel frame with 5mm thick steel panels. This tank is mounted on a horizontal shake table.

Fig 2: View of Shake table, Surcharge Weights and Piezometers

The platform with wheels rests on four knife edges being rigidly fixed on two pairs of rails anchored to the foundation. This is driven in horizontal direction by a 3 H.P. A.C. motor through crank mechanism, for changing rotary motion into translatory motion. The amplitude of motion can be changed through two eccentric shafts. By changing the relative position of two shafts, the amplitude can be fixed as desired. The hand brake assembly is used for stopping the shake table. The pore pressure transducers were tried in experimental work for reading rise in pore water pressure, but due to overburden and sensitivity of the transducer, the observations given by transducers were not satisfactory. Therefore the pore pressure measurement was performed with the help of glass tube piezometer of 5 mm diameter, attached to the tank through rubber tubes at heights of 80 mm, 180 mm and 260 mm (B, M, T). These tubes were attached to steel pipes placed in the tank through side of wall of tank. At mouth of each steel pipe, a porous stone was wrapped, so as to allow rise in pore water pressure through this stone and finally, it could be measured through piezometer. The shake table could produce steady state vibrations. The maximum amplitude of horizontal acceleration which could be generated in the shake table was up to 0.3 g. The shake table could be shaked at 4 Hz, 8 Hz & 12 Hz frequency.

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• Preparation of sample

Firstly 150 liters of clean water was filled in the tank. Air bubbles in the piezometer tube were removed. Porous stone wrapped in filter paper was tied at mouth of steel pipe attached with piezometer through a rubber tube so that no sand particles pass and choke the tube. The porous stone before placing in steel tube was kept in boiled water for 5-10 minutes to remove air present, if any, in the pores of porous stone. After that, 480 kg of air dried sand was allowed to fall in tank to obtain 500 mm height of sample with the help of a funnel. After all the sand had settled in tank, the water overlying the sand deposit was removed by using a sponge. This water removed from top of sand layer was weighed for density calculation.

• Initial Relative Density of Sample

Tests were performed keeping the relative density (Dr) of sand as 35 %, 50% and 65% respectively. The density in the sample was maintained as per guidelines of ASTM D 5311-92(Reapproved 2004) and Ishihara (1996): Firstly 150 liters of water were filled in the tank, which was sufficient to submerge all three piezometer tubes. The relative density (Dr) of sand is defined by:

Dr = (emax - e) / (emax - emin) (1)

Where emax is the maximum void ratio, emin is the minimum void ratio and e is the desired void ratio at a particular Dr. The void ratio (e) corresponding to Dr = 35% was calculated using:

e = emax – Dr (emax - emin) (2)

The values of emax and emin were 0.86 and 0.48 respectively for the test sand used in the study. Knowing the value of void ratio (e) from above, dry unit weight of sand (γd) was determined by the following equation:

γd = G. γw / (1+ e ) (3)

For the soil used in this study, G = 2.65 and γw = 9.81 kN/m3. The value of dry unit weight (γd) for Dr as 35%, 50% and 65% were 15.34 kN/m3, 15.86 kN/m3and 16.43 kN/m3 respectively. Taking constant height of sand sample in the tank i.e. 500 mm, the volume (V) occupied by the sand in the tank was determined using the plan dimensions of tank i.e. 1060 mm x 600mm. The dry weight of sand (Wd) was determined by the equation:

Wd = (γd. V) (4)

It was found that weight of dry sand required for Dr = 35%, 50% and 65% were 484 kg, 500 kg and 517 kg, respectively. The same procedure was used for cyclic triaxial tests.

• Shaking Duration

Seed and Idriss (1982) gave empirical correlation of magnitude of earthquake to its duration as follows;

Magnitude 6 6.5 7 7.5 8 8.5 Duration(sec) 5 8 11.5 15 21 26

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From above table we can say that duration and magnitude of earthquake relation can be used for dynamic studies related to soil liquefaction. This criterion for shaking duration was adopted in the study.

CYCLIC TRIAXIAL TESTS

Computerized triaxial testing facility available at IISC, Bangalore with the option of both static and dynamic testing was used to conduct experiments on small size specimen. The triaxial cell is built with a low friction piston rod seal to which a servo-controlled submersible load cell is fitted. The loading system consists of a load frame and hydraulic actuator capable of performing strain controlled tests with a frequency range of 0.01Hz to 10 Hz employing built in sine triangular forms.

Fig. 3.0: Cyclic Triaxial Apparatus at IISC, Bangalore

The conditioned output from the sensor is received by process interface, which forms the communication link between the computer and the loading system. Fig. 3.0 shows the photographic view of details of the system.

TEST PROCEDURE

The tests had been performed at an acceleration values of 0.1 to 0.3g and at a frequency of 4 Hz. Before imparting the shaking, the values of pore water pressures rise in all the three piezometer were recorded. The rise in pore water pressures were recorded after shaking, till these got constant. All the tests were conducted at confining pressure of 100 kPa with cyclic sine wave loading at frequency of 1 Hz and 0.18% shear strain.

RESULTS AND CONCLUSIONS

287

The results of experimental studies related to unreinforced sand prepared at relative densities of 35%, 50% and 65% are presented below. All of these effects were studied at different levels of acceleration i.e. 0.1 g, 0.2 g and 0.3 g. Cyclic Triaxial tests results were used as validation purpose of Shake Table tests.

• Effect of Relative Density

The variation of excess pore water pressure at acceleration level of 0.1 g to 0.3 g has also been presented in Figs. 4.0 (a-c) for unreinforced sand samples prepared at 35%, 50% and 65%, relative density respectively. With increase in relative density, the average excess pore pressure had come down from 3.31 kN/m2 (For Dr = 35% of unreinforced sand) to 2.76 kN/m2 (For Dr = 50% of unreinforced sand) & 1.98 kN/m2 (For Dr = 65% of unreinforced sand) at 0.1g. This decrease was due to increase in dry unit weight from 15.34 kN/m3 (For Dr = 35% of unreinforced sand) to 15.86 kN/m3 (For Dr = 50% of unreinforced sand) and 16.34 kN/m3 (For Dr = 65% of unreinforced sand) respectively. This decrease may also be attributed to increase in angle of internal friction from 300 to 320 & 360 for 35% to 50% & 65% increase in relative density respectively. Moreover, rearrangement of sand particles from random to parallel direction takes place to form closer packing. The same trend of results was obtained by Mittal (1988). In case of cyclic tests, it was be observed that number of cycles increased from 80 (for relative density as 35%) to 180 and 240 (for relative density as 50% and 65%) respectively for initial liquefaction, as seen from Fig. 5.0 (a-c). The reason may be that an increase in relative density results in an increased cyclic strength at a given confining. Similar results were reported by Krishnaswamy & Issac (1995)

• Effect of Acceleration

In Fig 4.0 (a), one of the curves shows an increasing trend of pore pressure from 3.31 kN/m2 to 3.64 kN/m2 with increase in acceleration from 0.1 g to 0.3 g at 35% relative density, which means soil had been liquefied. Ohara (1960) and Gupta (1977) also had similar observations on pore pressure rise versus acceleration.

• Effect of Frequency

The effect of frequency on liquefaction behaviour of sand has been discussed in Fig. 4.0 (a-c). To establish the effect of frequency on liquefaction behaviour of unreinforced sand, tests were conducted on two frequencies i.e. 4 Hz and 8 Hz. For instance at 0.2 g, the average excess pore pressure at frequency level of 4 Hz and 8 Hz were 3.4 kN/m2 and 4.82 kN/m2 respectively at 35% relative density. This means that pore pressure development also depends upon frequency of dynamic load. Kumar and Samui (2008) have also reported same behaviour of pore pressure with frequency excitation. It can be observed that in general, pore water pressure increases with time, reaches maximum value and then dissipates quickly.

(a) (a) R.D = 35%

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(b) For R.D = 50%

(c) For R.D = 65%

Fig. 4.0 (a to c): Excess Pore Pressure Vs Acceleration

(a) Dr = 35%

(b) Dr = 50%

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(c) Dr = 65%

Fig. 5.0: Variation of Excess Pore Pressure of Unreinforced Sand with Number of Cycles

References

Casagrande, A., (1940), “Seepage through dams.” Contribution to Soil Mechanics 1925–1940, Boston Society of Civil Engineers, Boston.

Castro, G., (1969), “Liquefaction of Sands,” Harvard Soil Mechanics Series 87, Harvard University, Cambridge, Massachusetts

Florin, V. A., and Ivanov, P.L. (1961), “Liquefaction of saturated sandy soils”, Proc. of the Fifth Int. Conf. on Soil Mechanics and Foundation Engineering, Paris, France, Vol. 1, pp. 107-111.

Gupta, M. K. (1977), “Liquefaction of Sands during Earthquake”, Ph.D. Thesis, Dept. of Civil Engineering, University of Roorkee, Roorkee, India.

Krishnaswamy, N.R. and Isaac, N. T. (1995), “Liquefaction analysis of saturated reinforced granular soils”, Journal of Geotech. Engineering, ASCE, Vol. 121(9), 645-651.

Martin, G. R., Firm, W.D.L. and Seed, H.B. (1975), “Fundamentals of liquefaction under cyclic loading”, Journal of Geotechnical Engineering, ASCE, Vol. 101 (5), 423-438.

Prakash, S. (1981), “Soil Dynamics” McGraw Hill Book Co., Singapore.

290

SEISMIC MODELING IN SOIL STRUCTURE INTERACTION CONTINUUM

Harpal Singh Department of Civil Engineering, Guru Nanak Dev Engineering College, Ludhiana

Abstract: A large number of research papers and several books have been written on structure-foundation-soil analysis and site response due to earthquake loading. However, the majority of these publications have been restricted to the linear behavior of soil-structure systems. It is possible, with the use of the numerical methods presented here, to conduct accurate earthquake analysis of real soil-structure systems in the time domain, including many realistic nonlinear properties. Also, it can be demonstrated that the solution obtained is converged to the correct soil-structure interactive solution.

INTRODUCTION

Most of the civil engineering structures involve some type of structural element with direct contact with ground. When the external forces, such as earthquakes, act on these systems, neither the structural displacements nor the ground displacements, are independent of each other. The process in which the response of the soil influences the motion of the structure and the motion of the structure influences the response of the soil is termed as soil-structure interaction (SSI) [Tuladhar (2006)].

Conventional structural design methods neglect the SSI effects. Neglecting SSI is reasonable for light structures in relatively stiff soil such as low rise buildings and simple rigid retaining walls. The effect of SSI, however, becomes prominent for heavy structures resting on relatively soft soils for example nuclear power plants, high-rise buildings and elevated-highways on soft soil [Wolf(1985)].

Damage sustained in recent earthquakes, such as the 1995 Kobe Earthquake, have also highlighted that the seismic behavior of a structure is highly influenced not only by the response of the superstructure, but also by the response of the foundation and the ground as well [Myloakis (2000)]. Hence, the modern seismic design codes, such as Standard Specifications for Concrete Structures: Seismic Performance Verification JSCE 2005 stipulate that the response analysis should be conducted by taking into consideration a whole structural system including superstructure, foundation and ground.

EFFECT OF SOIL STRUCTURE INTERACTION ON STRUCTURAL RESPONSE

It has conventionally been considered that soil-structure interaction has beneficial effect on the seismic response of a structure. Many design codes have suggested that the effect of SSI can reasonably be neglected for the seismic analysis of structures [ATC-3(1978) & NEHRP (1997)]. This myth about SSI apparently stems from the false perception that SSI reduces the overall seismic response of a structure, and hence, leads to improved safety margins. Most of the design codes use over simplified design spectrums, which attain constant acceleration up to a certain

291

period, and thereafter decreases monotonically with period. Considering soil-structure interaction makes a structure more flexible and thus, increasing the natural period of the structure compared to the corresponding rigidly supported structure. Moreover, considering the SSI effect increases the effective damping ratio of the system. The smooth idealization of design spectrum suggests smaller seismic response with the increased natural periods and effective damping ratio due to SSI. With this assumption, it was traditionally been considered that SSI can conveniently be neglected for conservative design. In addition, neglecting SSI tremendously reduces the complication in the analysis of the structures which has tempted designers to neglect the effect of SSI in the analysis.

This conservative simplification is valid for certain class of structures and soil conditions, such as light structures in relatively stiff soil. Unfortunately, the assumption does not always hold true. In fact, the SSI can have a detrimental effect on the structural response, and neglecting SSI in the analysis may lead to unsafe design for both the superstructure and the foundation [Myloakis et. al (2000)].

• Detrimental effects of SSI

Using rigorous numerical analyses, Myloakis et. al (2000) have shown that increase in natural period of structure due to SSI is not always beneficial as suggested by the simplified design spectrums. Soft soil sediments can significantly elongate the period of seismic waves and the increase in natural period of structure may lead to the resonance with the long period ground vibration. Additionally, the study showed that ductility demand can significantly increase with the increase in the natural period of the structure due to SSI effect. The permanent deformation and failure of soil may further aggravate the seismic response of the structure.

When a structure is subjected to an earthquake excitation, it interacts with the foundation and the soil, and thus changes the motion of the ground. Soil-structure interaction broadly can be divided into two phenomena: a) kinematic interaction and b) inertial interaction. Earthquake ground motion causes soil displacement known as free-field motion. However, the foundation embedded into the soil will not follow the free field motion. This inability of the foundation to match the free field motion causes the kinematic interaction. On the other hand, the mass of the super-structure transmits the inertial force to the soil causing further deformation in the soil, which is termed as inertial interaction [Wolf(1985)].

At low level of ground shaking, kinematic effect is more dominant causing the lengthening of period and increase in radiation damping. However, with the onset of stronger shaking, near-field soil modulus degradation and soil-pile gapping limit radiation damping, and inertial interaction becomes predominant causing excessive displacements and bending strains concentrated near the ground surface resulting in pile damage near the ground level [Myloakis et. al (2000)].

Observations from recent earthquakes have shown that the response of the foundation and soil can greatly influence the overall structural response. There are several cases of severe damages in structures due to SSI in the past earthquakes. Yashinsky [1998] cites damage in number of pile-supported bridge structures due to SSI effect in Loma Prieta Earthquake in San Francisco in 1989. Extensive numerical analysis carried out by Myloakis et. al (2000) have attributed SSI as one of the reasons behind the dramatic collapse of Hanshin Expressway in 1995 Kobe Earthquake.

KINEMATIC OR SOIL STRUCTURE INTERACTION

292

The most common soil-structure interaction SSI approach, used for three dimensional soil-structure systems, is based on the "added motion" formulation [Clough et.al 1993]. This formulation is mathematically simple, theoretically correct, and is easy to automate and use within a general linear structural analysis program. In addition the formulation is valid for free-field motions caused by earthquake waves generated from all sources. The method requires that the free-field motions at the base of the structure be calculated prior to the soil-structure interactive analysis.

Consider the case where the SSI model is divided into three sets of node points. The common nodes at the interface of the structure and foundation are identified with “c”; the other nodes within the structure are “s” nodes; and the other nodes within the foundation are “f” nodes. From the direct stiffness approach in structural analysis, the dynamic force equilibrium of the system is given in terms of the absolute displacements, U , by the following sub-matrix equation. U = v +u (1)

U = Absolute Displacements v = Free Field Displacements u = Added Displacements

where the mass and the stiffness at the contact nodes are the sum of the contribution from the structure (s) and foundation (f), and are given by Mcc =M(

ccs) + M(

ccf ) and Kcc = K(

ccs) +K(

ccf ) (2)

The dynamic equilibrium equations, with damping added, can be written in the following form: MÜ + CÚ + KU = R (3)

Added Structure (s)

Common Nodes (c)

Soil Foundation System (f)

U = v +u U = Absolute Displacements v = Free Field Displacements u = Added Displacements

u = 0

Fig 1: Soil-Structure Interaction Model

293

ANALYSIS OF GRAVITY DAM AND FOUNDATION

In order to illustrate the use of the soil-structure interaction option several earthquake response analyses of the Pine Flat Dam were conducted with different foundation models. The foundation properties were assumed to be the same properties as the dam. Damping was set at five percent. A finite element model of the dam on a rigid foundation is shown in Figure 2.

The two different foundation models of dam with small and large foundations used are shown in Figure 3. Selective results are summarized in Table.1. For the purpose of comparison, it will be assumed that Ritz vector results, for the large foundation mesh, are the referenced values. The analysis has been carried out with SHAKE (1970)

The differences between the results of the small and large foundation models are very close which indicates that the solution of the large foundation model may be nearly converged. It is true that the radiation damping effects in a finite foundation model are neglected. However, as the foundation model becomes larger, the energy dissipation due to normal modal damping within the massive foundation is significantly larger than the effects of radiation damping for transient earthquake type of loading.

Fig 2: Finite Element Model of Dam only

• The Massless Foundation Approximation

Most general purpose programs for the earthquake analysis of structures do not have the option of identifying the foundation mass as a separate type of mass on which the earthquake forces do not act. Therefore, an approximation that has commonly been used is to neglect the mass of the foundation completely in the analysis. Table 2 summarizes the results for an analysis of the same dam-foundation systems using a massless foundation. As expected, these results are similar. For this case the results are conservative; however, one cannot be assured of this for all cases.

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Fig 3: Models of Dam with Small and Large Foundation

Table 1: Selective Results of Dam-Foundation Analyses

DAM WITH SMALL LARGE NO Foundation Foundation Foundation

TOTAL MASS lb-sec2/in 1,870 13,250 77,360

PERIODS seconds 0.335 0.158 0.404 0.210 0.455 0.371

Max. Displacement inches 0.65 1.28 1.31

Max & Min Stress ksi -37 to +383 -490 to +289 -512 to +297

Table 2: Selective Results of Dam With Massless Foundation Analyses

DAM WITH SMALL LARGE

NO Foundation Foundation Foundation

TOTAL MASS lb-sec2/in 1,870 1,870 1,870

PERIODS seconds 0.335 0.158 0.400 0.195 0.415 0.207

Max. Displacement inches 0.65 1.27 1.43

Max & Min Stress ksi -37 to +383 -480 to +289 -550 to +330

SUMMARY

A large number of research papers and several books have been written on structure-foundation-soil analysis and site response due to earthquake loading. However, the majority of these publications have been restricted to the linear behavior of soil-structure systems. It is possible, with the use of the numerical methods presented here, to conduct accurate earthquake analysis of real soil-structure systems in the time domain, including many realistic nonlinear properties. Also, it can be demonstrated that the solution obtained is converged to the correct soil-structure

295

interactive solution.

For major structures on soft soil one dimensional site response analyses should be conducted. Under major structural elements, such as the base of a shear wall, massless elastic springs should be used to estimate the foundation stiffness. For massive structures, such as gravity dams, a part of the foundation should be modeled by three dimensional SOLID elements in which SSI effects are included.

References

ATC-3(1978). Tentative Provisions for the Development of Seismic Regulations of Buildings: A Cooperative Effort with the Design Profession, Building Code Interests, and the Research Community, National Bureau of Standards, Washington DC.

Japan Society of Civil Engineers. Standard Specifications for Concrete Structures – 2002: Seismic Performance Verification. JSCE Guidelines for Concrete No. 5, 2005

J. Hart. and E. Wilson “WAVES (2005) - An Efficient Microcomputer Program for Nonlinear Site Response Analysis", National Information Center for Earthquake Engineering, Davis Hall, University of California, Berkeley, Tel. # (415) 642-5113.

NEHRP (1997) Recommended provisions for seismic regulations for new buildings and other structures, Part 1 and 2, Building Seismic Safety Council, Washington DC

Mylonakis, G. and Gazetas, G.(2000). Seismic soil structure interaction: Beneficial or Detrimental? Journal of Earthquake Engineering, Vol. 4(3), pp. 277-301

Mylonakis, G., Gazetas, G., Nikolaou, S., and Michaelides,O. (2000). The Role of Soil on the Collapse of 18 Piers of the Hanshin Expressway in the Kobe Earthquake, Proceedings of 12th World Conference on Earthquake Engineering, New Zealand, Paper No. 1074

R. Clough, and J. Penzien, Dynamics of Structures, Second Edition, McGraw-Hill, Inc., ISBN 0-07-011394-7, 1993.

"SHAKE - A Computer Program for the Earthquake Response for Horizontally Layered Sites", by P. Schnabel, J. Lysmer and H. Seed, EERC Report No. 72-2, University of California, Berkeley, February 1970.

Tuladhar, R. (2006). Seismic behavior of concrete pile foundation embedded in cohesive soil, Ph.D. Dissertation, Saitama University, Japan.

Yashinsky, M.(1998). The Loma Prieta, California Earthquake of October 17, 1989 – Highway Systems, Professional Paper 1552-B, USGS, Washington

Wolf, J. P. (1985). Dynamic Soil-Structure Interaction. Prentice-Hall, Inc., Englewood Cliffs, New Jersey.

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A CASE STUDY OF CLOSELY SPACED EXACTLY IDENTICAL STRUCTURES WITH DIFFERENT FOUNDATIONS ON

EXPANSIVE SOIL

A Kameshwar Rao*,S M Jalali**, Sneha Rao***,Rahul Patidar**** and Priyanka Jain*****

* Engineer in Charge, C&S Divn,RRCAT,Dept of Atomic Energy,Indore (M P) 452 013. **Superintending Engineer C&S Divn,RRCAT,Dept of Atomic Energy,Indore (M P) 452 013.

*** Strategic Analyst, Bangluru,560 005 **** Financial Consultant Capital One Bangluru, 560 005

***** Consulting Engineer, New Delhi 110001 Abstract: Expansive soils are recognized as the most problematic soil world over and more so for tropical countries like India. The structural damage to the buildings is caused by differential heave as a consequence of variation in moisture content of expansive soil.Malwa region of Madhya Pradesh has a large belt of expansive soil hence engineers of this region encounter the problems posed by the locally available soil. The problem gets further aggravated at few locations where water table is met at shallow depth. The paper makes an effort to put forth as to what caused the designer to adopt two different type of foundation for six closely spaced exactly identical multi storied structures, although all were founded on expansive soil. The paper briefly discusses various other possible options along with comparison of cost and finally brings out some useful inferences.

INTRODUCTION

Six apartments, each ground + two, R C C framed structure of 9.50m height and each having plinth area of 900 m2 were constructed during year 2003 to year 2007.Three apartments were located at site no. I while remaining three are located at site no. II, which is quite close to first site. The geotechnical parameter of soil on which foundation rests is indicated in table 1.

Table 1: Geotechnical parameters of site I and site II

S. No. Parameters Site I Site II

(1) Grain Size Gravel- 1.92 % Sand - 12.71 % Silt- 76.27 % Clay- 9.10 %

Gravel- 1.41 % Sand - 4.59 % Silt- 82.71 % Clay- 12.39 %

(2) Atterberg’s Limit Liquid Limit – 51 % Plastic Limit- 21 % Shrinkage Limit- 13 % Plasticity Index- 30

Liquid Limit – 64 % Plastic Limit- 21 %

Shrinkage Limit- 11 % Plasticity Index- 43

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(3) Swelling properties Swelling index -1.65 Heave – 16 cm

Swelling pressure- 36 t/sqm

Swelling index – 2.11 Heave – 27 cm

Swelling pressure- 43 t/sqm (4) Max dry density 1.44 gms per cu cm 1.44 gms per cu cm (5) CBR soaked 3.60 % 2.80 % (6) SBC at 2.0 m depth 10 t/sqm 5 t/sqm (7) Water table 569.70 m Fluctuates in the range of 569.7

m to 572 .30 m

It can be easily concluded from above data that the soil strata over which foundation was to rest is highly expansive in nature as it predominantly contains Montmorillonite clay mineral. Such soil is highly sensitive to moisture content. Site II is therefore more complicated due to large fluctuations in water table.

VARIOUS OPTIONS FOR FOUNDATION ON EXPANSIVE SOILS:

Many research scholars have suggested various solutions however each site being unique, none of the following methods should be followed blindly:

(a) CNS and MSM concept developed by Dr R K Katti; CBRI Roorkee. (b) Pre-wetting as suggested by Dr A.N.Patel, Director, KCBITS, Indore. (c) Lengthening the path of seasonal moisture change as suggested by O Neill &

Poormoayed. (d) R C C under reamed pile foundation developed by Dr Dinesh Mohan, CBRI Roorkee. (e) R C C raft foundation. (f) Isolated R C C footing. (g) Granular pile anchoring suggested by Dr A Sri Rama Rao, N. Babu Shankar and

Ramana Murthy to anchor the foundation which may be either (e) or (f). (h) R C C friction pile anchoring suggested by authors to anchor the foundation which may

be either (e) or (f). These methods are briefly described.

• CNS & MSM concept

The depth at which effect of moisture is insignificant as far as heave and swelling pressure are concerned is termed as self equilibrating depth. The phenomenon of self equilibrating depth is attributed to the combined effect of Newtonian & Columbian forces existing in saturated clayey soil. In general Newtonian force which is weight of soil acting downward is of the order of 1.5 tonne to 2.2 tonne per sqm while upward swelling pressures are 36 tonne & 43 tonne per sqm respectively. Balance upward force which is quite large, is resisted by Columbian forces, developed due to internal cohesive bond around expansive clay minerals and interfacing moisture. Katti has proved and demonstrated that designed thickness of CNS layer can prevent transmission of heave and swelling pressure. As per studies carried out by Dr Katti, Cohesive Non swelling Soil (CNS) layer technology has been found successful. Katti has developed semi log graph which gives thickness of CNS for a particular heave. The designed foundation is laid over CNS.It is a fact that underlying soil has more shearing strength & SBC than sandwiched CNS. The CNS has voids to produce cohesive bond.Dr Katti has therefore suggested if required a combination of CNS & MSM (Mechanically Stabilized Mix) may be used for which he has developed separate curves. CNS & MSM combination significantly improves the SBC.

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Katti has however cautioned that the work should be carried out before or after monsoon as in case of rains during excavation the accumulated water on the bottom of pit starts heaving up to new self equilibrating depth. Further the material to be used as CNS+MSM must meet criteria specified by Katti which may be a difficult issue some times.

• Pre-wetting

The strata on which foundation is to be cast is flooded for some period thus maximum possible swelling conditions are induced. The reinforcement of footings are kept ready and lowered in the ditch. Before commencing the casting of footing, the ditch is dewatered. Suitable admixtures are used for quick setting. When the structure is loaded swelled soil does not give any counter effect. However the reliability of this method has been established in field for two storied construction thus further studies are needed.

• Lengthening the path of seasonal moisture change

As suggested by O Neill & Poormoayed this is an effective method. During sixties only plinth protection was considered sufficient but in case of structures on expansive soil, in addition to plinth, a cut off wall is essential. The depth of cut off wall can be easily determined using Bligh’s theory. This system has exhibited encouraging results in Malwa region.

• R C C under reamed pile foundation

Developed by Dr Dinesh Mohan of CBRI Roorkee in 1961, this type of foundation has become the most common. In case of small structures say up to three stories, there is a general tendency to avoid testing of piles. As per a study (unpublished) carried out by Dr A N Patel 23 % of the piles surveyed were found to possess honeycomb and soil surrounding bulb heaved. This is however not the drawback of the system but result of negligence at site. The piles are designed as per I S 291.

• R C C raft

Expansive soils usually have very low SBC.In such cases plan area of isolated footings is more than 50 % of the plan area and thus R C C raft becomes the best choice. The raft proves advantageous as it can counter unequal settlements even if it is caused by heave or swelling pressure. This foundation was therefore provided at site I of case under study.

• Isolated R C C footing

As already stated the expansive soils usually have very low SBC. In such cases plan area of isolated footings is more than 50 % of the plan area and thus R C C raft becomes the best choice. However in case if water table is met at shallow depth, the raft is required to be checked to resist uplift. The thickness of raft is dominated by uplift force. As the uplift depends upon the area of foundation hence thickness of raft increases. In such cases although plan area of footing exceeds 50 %, one has to consider isolated footing since to resist uplift; thickness of footing shall not increase much as area of individual footings is very less as compared to area of raft. This is a very

299

important finding and has been applied at site II of case under study thus economizing without compromising safety.

• Granular pile anchoring

The use of granular has been very common on soft clay or loose sand strata. Dr A Sri Rama Rao, N. Babu Shankar and Ramana Murthy from JNTU Kakinada have carried out experimental work showing that if granular piles are provided in expansive soil, they will not be able to resist uplift. In order to resist the upward force which is tensile in nature; a mild steel plate connecting regular foundation through a mild steel rod surrounded by granular pile as shown shall anchor the foundation whether it is an isolated footing or a raft. The numbers and sizes of plates and the rods can be easily designed.

• R C C friction pile anchoring

In case if water table is met at shallow depth, the foundation whether it is an isolated footing or a raft is required to be checked to resist uplift. The thickness of raft or footing is dominated by uplift force. If thickness is very high than it is worth to anchor the foundation with precast or cast in situ piles. In such a case uplift is resisted mostly by friction pile while the load of structure shall be borne by the regular foundation. We agree some more experimental study for the same is needed. This option appears to be the safest option.

COST COMPARISON

Various options discussed above have been evaluated to work out cost economics. The sizes were finalized after conducting stability analysis to avoid tilting, overturning, sliding and uplift. The dimension of foundation is so proportioned to ensure that max pressure as sum total of bearing pressure and bending pressure in two orthogonal directions does not exceed ‘SBC’. An imaginary structure of size 6.00 m x 6.00 m and of height 9.00 m height having 200 mm x 200 mm column spaced @ 3.00 m centre to centre with 200 mm thick non load bearing brick wall has been chosen for comparison. The table 2 indicates the comparison of cost involved in both options:

Table 2: Abstract of cost for site I and site II

Sr no.

Option under consideration Cost of foundation in Indian ` at 2007

Comparison of cost with respect to the cost as per option (g) i.e. isolated footing

(a) CNS & MSM concept + isolated footings over it. 33000.00 1.50 (b) Pre-wetting = Cost of isolated footings + cost of

watering/dewatering + quick setting compound = 24000.00 1.10

© Lengthening the path of seasonal moisture change = Cost of isolated footings + cost of plinth protection + cost of cut off wall

32000.00 1.45

(d) R C C under reamed pile foundation with cap 24000.00 1.10 (e) R C C Raft 67000.00 3.00 (f) R C C raft for shallow water table conditions 125000.00 5.67 (g) Isolated R C C footing 22000.00 1.00 (h) Isolated R C C footing for shallow water table 24000.00 1.10

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(i) Granular pile anchoring = Cost of isolated footings + cost of granular pile + cost of mild steel work

28000.00 1.28

(j) R C C friction pile anchoring the isolated footing 40000.00 1.80

It may be seen from our table that isolated column footing proves to be the most economical if shallow water table conditions are not prevailing. In case of shallow water table isolated column footing is most economical option along with few other options. Among other options some are yet to be time tested while some others have inherent limitations.

CONCLUSION

The most important findings put forth in this paper is that even though two structures were exactly identical in all respect and located almost in the same condition, the foundation had to be re-designed due to fluctuating water table conditions. Change in one parameter that is water table has shifted the choice from R C C Raft to R C C isolated footing. It may be seen from the table that R C C Raft was a costly option in any case but it turn out to be terrifically costliest option in case of shallow water table conditions. It was therefore not recommended in the second site.

Had the foundation of second site was not designed taking in to consideration of uplift, the details of R C C Raft (Option e) of first site would have been followed since structure, usage etc were same. This would have perhaps resulted in failure as effect of uplift pressure is significant. It gives a very important lesson not to follow any design blindly as change in one parameter necessitates thorough review. It is very clear that conventional foundation analysis may not prove enough if expansive soil with fluctuating water conditions prevail at site. Failure of several structures could have been avoided if the results of soil investigations are not looked as mere rituals.

ACKNOWLEDGEMENT

The authors are grateful to RRCAT officials for providing inspiration, motivation, valuable guidance and finally reviewing the paper. The paper could not have taken this shape without untiring guidance provided by Dr A N Patel, a leading Geo technologist,farmer chairman I G S Indore & Director K C Bansal Institute of Technology & Science, Indore.

References

Guidelines for exploration, design and construction of foundation on expansive soils for light structures by Dr R.K.Katti, published in National Seminar on expansive soil organized by IGS Indore in May 1998.

Soil Mechanics and foundations by B.C.Punmia, Laxmi Publications, New Delhi. Granular Pile anchors-An effective foundation in expansive soil by Dr A Srirama Rao published in

National Seminar on expansive soil organized by IGS Indore in May 1998. Free heave measurements in expansive soil by N.Babu Shankar & Ramana Murthy published in

National seminar on partially saturated soils and expansive soils organized by IGS Kakinada in 1996.

Problems of floor on expansive soil-Causes & Remedies by Dindorkar & Dr A N Patel, published in a journal titled New Building Materials and construction world vol 2 (VII)-1997.

Methodology for foundation on expansive clays by O Neill & Poormoayed published in journal JGE, ASCE, DEC, 106 (GT 12) in 1980.

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BEARING CAPACITY OF SHALLOW FOUNDATION ON SLOPE:

A REVIEW

Dhiraj Raj* and M. Bharathi ** *Research Scholar, Dept. of Earthquake Engg., IIT Roorkee

**Assistant Professor, School of Civil Engg., LPU

Abstract: In developing country like India, with the tremendous increase in population and scarcity of plain land, development in hilly regions turns out to be a major issue. With the vast development of infrastructure in hilly region the safety of the buildings on slopes has to be given more importance because there are no BIS guidelines for designing shallow foundations resting on slopes. It is necessary to distinguish between the behaviours of shallow foundation on slope and on plain ground. Estimation of bearing capacity of shallow foundation is an important parameter in the design of any structures. Construction of footing on slope is different from the plain ground. A few research works had been carried out for the estimation of bearing capacity on slope and near slope. The method for bearing capacity estimation on sloping ground was first proposed by Meyerhof and later on many researchers had contributed in this area. In this paper, the methods available for the estimation of bearing capacity of shallow foundation on slope and near slope are discussed. The formation of different failure surfaces and the bearing capacity of shallow foundation are obtained considering the geometry of the foundation, slope and soil properties. From the study, it is found that the method which gives the minimum bearing capacity for shallow foundation on slope is considered for conservative design.

INTRODUCTION

Civil engineering structures are often forced to be constructed on slopes, adjacent to slopes or near the proposed excavation. This trend is more marked in hilly regions of India. The investigation of bearing capacity of loaded slopes is very important in this case because they are more susceptible to fail than other type of earth structures. Generally for the small to medium rise buildings, shallows foundations are frequently used. In such situation, the problem is to obtain the minimum value of the bearing capacity: (1) from foundation failure; and (2) from overall stability of the slope. In case of noncohesive soils, the bearing capacity is always governed by foundation failure, while in cohesive soil the bearing capacity of the foundation may be dictated by the stability (Saran et al., 1989). These days various methods proposed by the researchers are available to find the bearing capacity of shallows foundation on slope or near slope, which are based on: (1) Limit equilibrium analysis; (2) Slip line analysis; (3) Limit analysis; and (4) Finite element analysis. The method for bearing capacity estimation on sloping ground was first proposed by Meyerhof (1957) and later on many researchers had contributed in this area. In this paper, the methods available for the estimation of bearing capacity of shallow foundation on slope and near slope are discussed chronologically.

Meyerhof (1957) proposed a theoretical solution to determine the ultimate bearing capacity of a shallow foundation located on face of the slope or near the top edge of the slope given by

302

Eqn. 1 and nature of plastic zones developed in soil under continuous foundation in both cases are shown in Table 1.

12ucqqqcNBN γγ=+ (1)

Where, cqN , qNγ = bearing capacity factors, can obtained from the chart shown in Table 1. Table 1: Failure Surfaces and Bearing Capacity Factors (Meyerhof, 1957)

On Face of the Slope Near Top of the Slope

β = slope angle with horizontal, abc = elastic zone, acd = radial shear zone, ade = mixed shear zone, c and φ = shear strength parameters of soil, γ = unit weight of soil, po and so = normal and shear stresses on plane ae, respectively

Df = depth of the foundation, H = height of the slope., B = width of foundation, b = distance of foundation from edge of slope.

Meyerhof’s bearing capacity factor cqN for a purely cohesive soil

Meyerhof’s bearing capacity factor cqN for a purely cohesive soil

b/B

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Meyerhof’s bearing capacity factor qNγ for a purely granular soil

Meyerhof’s bearing capacity factor qNγ for a purely granular soil

Hasen (1970) proposed the following relationship for the ultimate bearing capacity of a

continuous foundation located at the edge of the slope given by Eqn. 2; 12uccqqqcNqNBN ββγγβλλγλ=++

(2)

Where, fqD γ= Nc, Nq and Nγ are bearing capacity factors given by Eqn. 3-5 as

tan 1sin1sinqNe πφ φ

φ +

= − (3) (1)cotcqNN φ=− (4)

21.5tancNNγ φ= (5)

cβλ , qβλ and γβλ are slope factors given by Eqn. 6-8 as 2(1tan)qβγβλλβ==− (6)

11

qqc

q

NN

ββ

λλ

−=

− (For φ > 0) (7) 21

2cββ

λπ

=−+ (For φ = 0) (8)

Vasic (1975) concluded from his study that for frictionless soil (φ = 0) with the absence of

weight due to the slope, the bearing capacity factors Nγ has a negative value, as given in Eqn. 9. 2sinNγ β=− (9)

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Hence, for φ = 0, Nc = 5.14, Nq = 1, the ultimate bearing capacity is given as Eqn. 10 22(5.142)(1tan)sin(1tan)ufqcDB βγβγββ=−+−−− (10)

Kusakabe et al. (1981) compared their results with bearing capacities obtained by

conventional circular arc method and by Kotter’s stress characteristics equations and concluded that the upper bound solution was useful from engineering point of view because of simplicity of the method. A failure mechanism which was responsible for this problem is shown in Fig. 1, where β = slope angle, αB = distance from edge of slope, HB = slope height, hB = depth of failure point ‘A’on face of slope.

Fig. 1: Failure Mechanism Adopted for Upper Bound Solution

They used upper bound theorem of limit analysis method to find the bearing capacity of slope loaded on top surface given by Eqn. 11. By

12cqcNBN γγ=+

(11)

Where, Nc, Nγ = bearing capacity factors vary with the parameter( )/cBγ and are more effective for slope than the level ground. All the computed results were produced in the form of charts by Kusakabe et al. as shown in Table 2 for the use of design engineers. Table 2: Charts for Reduction Factor (µ) for Bearing Capacity Factors (Kusakabe et al., 1981)

φ 5.0cBγ=

1.0c

Bγ=

0.5c

Bγ=

0

305

10

20

30

40

Graham et al. (1988) provided a solution for the bearing capacity factor for a shallow continuous foundation on the top of a slope in granular soil based on the method of stress characteristics. The failure zones in the granular soil for embedment (Df/B) and setback (b/B) assumed for this analysis are shown in Fig 2.

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Fig. 2: Schematic diagram of failure zones for embedment and setback: (a) Df/B > 0; and (b) b/B

> 0

The ultimate bearing capacity was given by the Eqn. 12 as 12uqqBN γγ=

(12)

Where, qNγ = Bearing capacity factor, can obtained from Table 3.

Table 3: Design Charts for Bearing Capacity Factor qNγ (Graham et al., 1988) BC Factor Df/B b/B = 0 and b/B = 0.5 b/B = 1.0 and b/B = 2.0

qNγ 0

qNγ 0.5

qNγ 1.0

Saran et al. (1989) provided an analytical solution to obtain the bearing capacity of foundation adjacent to slopes using both limit equilibrium and limit analysis approaches

307

considering one sided failure along surface DEI as shown in Fig. 3, which is divided into two zones, viz. Zone I (elastic zone) and Zone II (combination of radial and passive shear bounded by a logarithmic spiral) and had presented the resulted in the form of non-dimensional charts. Both approaches gave almost same values and verified by performing tests. The ultimate bearing capacity was given by Eqn. 13 as

12ucqqcNqNBN γγ=++

(13)

Where, fqD γ= , Df = depth of foundation, B = foundation width, De = distance from edge of slope, φ = angle of internal friction, θ = log spiral angle, φ and φm = wedge angles, and Nc, Nq, Nγ are bearing capacity factors given in Table 4.

Fig. 3: Failure Surfaces and Forces on Wedges

Sarma and Chen (1995) used limit equilibrium method to derive the seismic bearing capacity factors for strip footing near sloping ground. The failure mechanism, as shown in Fig. 4, was composed of an active wedge and a passive wedge and a shared transition zone was sandwiched between the two wedges. The most critical failure mechanism was found by trial and error.

Fig. 4: Failure Mechanism and Applied Forces of Foundation-Soil System

The ultimate bearing capacity was given by Eqn. 14 as

0.5ucqqcNqNBN γγ=++ (14) Where, Nc, Nq, Nγ = Seismic bearing capacity factors, which are quadratic functions of the slope angle represented by Eqn. 15-17 as

2log() cNabc ββ=++ (15)

I

308

2log()tantanqNabc ββ=++ (16) 2log()tantanNabcγ ββ=++ (17)

Here a, b, c = constants of the quadratic functions and their values are different for Nc, Nq and Nγ , which were dependent on the friction angle and seismic coefficient.

Table 4: Bearing Capacity Factors (Saran et al., 1989)

Factor β (deg) Df/B b/B Soil Friction Angle φ (deg)

40 35 30 25 20 15 10 Nγ 30 0 0 25.37 12.41 6.14 3.20 1.26 0.70 0.10

20 53.48 24.54 11.62 5.61 4.27 1.79 0.45 10 101.74 43.35 19.65 9.19 4.35 1.96 0.77 0 165.39 66.59 28.98 13.12 6.05 2.74 1.14 30 0 1 60.06 34.03 18.95 10.33 5.45 0.00 — 20 85.98 42.49 21.93 11.42 5.89 1.35 — 10 125.32 55.15 25.86 12.26 6.05 2.74 — 0 165.39 66.59 28.89 13.12 6.05 2.74 — 30 1 0 91.87 49.43 26.39 — — — — 25 115.65 59.12 28.80 — — — — 20 143.77 66.00 28.89 — — — —

≤15 165.39 66.59 28.89 — — — — 30 1 1 131.34 64.37 28.89 — — — — 25 151.37 66.59 28.89 — — — —

≤20 166.39 66.59 28.89 — — — — Nc 30 1 0 12.13 16.42 8.98 7.04 5.00 3.60 —

20 12.67 19.48 16.80 12.70 7.40 4.40 — ≤10 81.30 41.40 22.50 12.70 7.40 4.40 — 30 1 1 28.31 24.14 22.5 — — — — 20 42.25 41.4 22.5 — — — —

≤10 81.30 41.4 22.5 — — — —

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Factor β (deg) Df/B b/B Soil Friction Angle φ (deg)

40 35 30 25 20 15 10 Nq 50 0 0 21.68 16.52 12.60 10.00 8.60 7.10 5.50

40 31.80 22.44 16.64 12.80 10.04 8.00 6.25 30 44.80 28.72 22.00 16.20 12.20 8.60 6.70 20 63.20 41.20 28.32 20.60 15.00 11.30 8.76

≤10 88.96 55.36 36.50 24.72 17.36 12.61 9.44 50 0 1 38.80 30.40 24.20 19.70 16.42 — — 40 48.00 35.40 27.42 21.52 17.28 — — 30 59.64 41.07 30.92 23.60 17.36 — — 20 75.12 50.00 35.16 27.72 17.36 — —

≤10 95.20 57.25 36.69 24.72 17.36 — — 50 1 0 35.97 28.11 22.38 18.38 15.66 10.00 — 40 51.16 37.95 29.42 22.75 17.32 12.16 — 30 70.59 50.37 36.20 24.72 17.36 12.16 — 20 93.79 57.20 36.20 24.72 17.36 12.16 —

≤10 95.20 57.20 36.20 24.72 17.36 12.16 50 1 1 53.65 42.47 35.00 24.72 — — — 40 67.98 51.61 36.69 24.72 — — — 30 85.38 57.25 36.69 24.72 — — —

≤20 95.20 57.25 36.69 24.72 — — —

Narita and Yamaguchi (1990) extended the log-spiral analysis of the bearing capacity for strip foundations placed on level ground, to those on the top the slopes. For analysis two types of failure (1. Toe and Slope failures 2. Base Failures) were considered as shown in Table 5. Comparison was also made with other analytical and experimental results to examine the applicability of the method to practical problem.

Table 5: Failure Types Considered for the Analysis (Narita and Yamaguchi, 1990)

Failure Type Schematic Diagram Explanation

Toe and Slope failures ( Log-spiral sliding surface)

O = Pole of log-spiral curve AE, B = 2b = Width of footing, L = λB = Distance from edge of slope, φ = Angle of internal friction of soil, β = Slope inclination, µ= tanφ, OA = ro, Equation of log-spiral

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Base Failures

exp()orr µθ= , Q = Ultimate load,

OADα =∠ , ω = Central angle depending on α, h = Depth of failure point from level ground on slope for first case, H = ηB = Height of small fill for second case, ∆W = Weight of triangular wedge of soil DGE,

Sarma and Chen (1995) used limit equilibrium method to derive the seismic bearing capacity factors for strip footing near sloping ground. The failure mechanism, as shown in Fig. 4, was composed of an active wedge and a passive wedge and a shared transition zone was sandwiched between the two wedges. The most critical failure mechanism was found by trial and error.

Fig. 4: Failure Mechanism and Applied Forces of Foundation-Soil System

The ultimate bearing capacity was given by Eqn. 14 as

0.5ucqqcNqNBN γγ=++ (14) Where, Nc, Nq, Nγ = Seismic bearing capacity factors, which are quadratic functions of the slope angle represented by Eqn. 15-17 as

2log() cNabc ββ=++ (15) 2log()tantanqNabc ββ=++ (16) 2log()tantanNabcγ ββ=++ (17)

Here a, b, c = constants of the quadratic functions and their values are different for Nc, Nq and Nγ , which were dependent on the friction angle and seismic coefficient.

Buhan and Garnier (1998) evaluated the bearing capacity of rectangular shallow foundation located near a slope or an excavation, by using yield design theory. The problem under consideration was a slope of height H and slope angle β, subjected to a vertical load Q applied on

311

upper surface by means of rigid rectangular foundation of length L and width B, placed at a distance D from the slope edge shown in Fig. 5.

Fig. 5: Bearing Capacity Problem of a Rectangular Footing Acting on Top of Slope

By considering the true three dimensional nature of the problem, two types of failure mechanism (viz. Instability failure mechanism and Punching failure mechanism) were selected, resulting in optimal upper bound estimate for the ultimate load bearing capacity of the foundation obtained through the implementation of the kinematic approach from outside. Based on this approach, a computational tool was also developed to provide a quantitative assessment of the bearing capacity reduction due to the slope proximity and then theoretical estimates were compared with experimental values obtained on full scale and centrifuge-reduced scale models.

Choudhury and Rao (2006) used limit equilibrium method to obtain the seismic bearing capacity factors for shallow strip foundation embedded in sloping ground with c-φ soil. Pseudostatic forces were considered acting on footing and on the soil below the footing as seismic forces. From the geometry, depending upon the values of the embedment ratio Df/B and slope angle β, three different types of composite failure surfaces (planar and log-spiral) shown in Table 6, were considered for analysis. The ultimate seismic bearing capacity qud is given by Eqn. 18 as

0.5udcdqddqcNqNBN γγ=++ (18) Where, Ncd, Nqd and Nγd = Seismic bearing capacity factors, which were obtained separately for various values of soil friction angles (φ) and seismic acceleration coefficients both in the horizontal (kh)and vertical directions (kv), ground inclinations (β), and embedment depths (Df).

Table 6: Failure Types Considered for the Analysis (Choudhury and Rao, 2006)

Failure Type Schematic Diagram Explanation

312

Type 1

ADE = Triangle wedge Zone I, DEF = Logarithmic spiral Zone II, DFG = Partial planar passive Zone

III, α 1 , α 2 = Base angles of elastic

wedge ADE, β = slope angle, Kh.qud.B = Horizontal force on

footing, (1-Kv).qud.B = Vertical force on

footing, β’ = angle GDM

Type 2

ADE = Triangle wedge Zone I, DEF = Logarithmic spiral Zone II depending on Df/B and β, α 1 , α 2 = Base angles of elastic

wedge ADE, β = slope angle, Kh.qud.B = Horizontal force on

footing, (1-Kv).qud.B = Vertical force on

footing, β’ = angle GDM

Type 3

ADE = Triangle wedge Zone I, DEF = Logarithmic spiral Zone II, DFG = Partial planar passive Zone

III, α 1 , α 2 = Base angles of elastic

wedge ADE, β = slope angle, Kh.qud.B = Horizontal force on

footing, (1-Kv).qud.B = Vertical force on footing, β’ = 0

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Georgiadis (2010) used finite element analysis based on limit equilibrium or upper bound plasticity calculations to investigate the influence of the various parameters that affect undrained bearing capacity of strip footings on or near undrained soil slopes as shown in Fig. 6, such as the distance of the footing from the slope, the slope height and the soil properties. The results of the analysis were compared to available methods. The obtained results were based on plane strain analyses using the program Plaxis Version 8.6. The three failure modes from the analysis are shown in Fig. 7. He also presented the results of analysis in the form of design charts as shown in Table 5.A design procedure was also proposed for the calculation of the undrained bearing capacity factor using the undrained shear strength and the bulk unit weight of the soil, the footing width, the distance of the footing from the slope, the slope angle and the slope height.

Fig. 6: Problem definition

Fig. 7: Failure modes: (a) and (b) bearing capacity failure and (c) overall slope failure

Table 7: Design Chart for Undrained Bearing Capacity of Strip Footing (Georgiadis, 2010)

Variation of Nc with λ for cu/γB = 0.5

Variation of Nc with λ for cu/γB = 1.0

314

Variation of Nc with λ for cu/γB = 1.5

Variation of Nc with λ for cu/γB = 2.0, 2.5 and 5.0

Yamamoto (2010) used the pseudo-static approach and the seismic forces consisted of a horizontal load applied to the foundation and the inertia of the soil mass. The seismic bearing capacity factors of spread and embedded foundations near slopes had been analytically investigated. The upper-bound method of limit analysis was employed and a non-symmetrical failure mechanism was proposed as shown in Fig. 8. This mechanism comprises a triangular active wedge, a logarithmic spiral shear zone and a passive wedge.

Fig. 8: Failure Mechanism Used in Analysis

The shear transfer coefficient was introduced to calculate the seismic bearing capacity of spread foundations with variable shear transfer at the base of foundations. The validity of the results from the present analysis was confirmed by comparing with the results proposed by other investigators. The upper bound of the seismic bearing capacity was expressed by Eqn. 19 as

12bcEE

PqcNBNB γγ==+

(19)

Where, cEN and ENγ are the lowest upper-bound solutions of the seismic bearing capacity factors of shallow foundations near slopes, as given in the form of design charts in Table 8 for practical use.

Table 8: Design Charts for Bearing Capacity factors (Yamamoto, 2010)

315

BC Factor

D/B α φ= 30o φ = 40o

ENγ 0 0

1 0

BC Factor

D/B α φ= 30o φ = 40o

cEN 1 0

316

0 ½

It had been also concluded the seismic bearing capacity factors reduce considerably with the increase of horizontal seismic coefficient. In addition, the magnitude of bearing capacity factors decreases further with increase in slope inclination and increase with the embedment and the distance of slope crest from the beginning of loading.

Castelli and Motta (2010) developed a model based on the limit equilibrium method considering a circular surface propagating towards the slope until the sloping ground was reached as shown in Fig. 9.

B = width of footing, d = distance from edge of footing, β = slope inclination, αi = angle of the base of the ith slice, ∆xi = width of the ith slice, Wi = weight of the ith slice, R = radius of the circular failure surface, Kv = vertical seismic coefficient, kh1 = horizontal seismic coefficient for limit load, kh2 = horizontal seismic coefficient for the soil mass, kh3 = horizontal seismic coefficient for the surcharge, n1 = number of slices under the footing, ntot = total number of slices, qlim = vertical limit load acting on the footing, qv = vertical surcharge, Ni = normal reaction at bottom of ith slice, Si = cohesive force at bottom of ith slice.

Fig. 9: Failure Mechanism and Applied Forces Adopted in Analysis

The static and seismic bearing capacity were investigated considering either the distance of the footing from the edge of the slope and/or the effect of the footing embedment and as a function of

317

the soil friction angle, of the seismic coefficient, of the sloping ground. The loading conditions consist in vertical and horizontal stress on the footing and on the soil below the footing. Both the inertial and kinematic effects of the seismic loading were considered for analyses, and a simple equation was derived for the evaluation of the seismic bearing capacity. The parametric analysis had also been carried on either in static and seismic conditions varying the friction angle of the soil (φ), the distance of the footing from the edge of the slope (d), the slope angle (β), the depth embedment of the footing (D) and the seismic coefficients.

Shiau et al. (2011) used the finite-element limit analysis method to obtain both lower and upper bound bearing capacity for strip footings placed on purely cohesive slopes. For a footing-on-slope system, the ultimate bearing capacity of the footing may be governed by either the foundation bearing capacity or the overall stability of the slope. The combination of these two factors makes the problem difficult to solve. The bearing capacity problem of a rigid foundation resting near a slope is illustrated in Fig. 10.

Fig. 10: Problem Notion and Potential Failure Mechanism

The study assumes the soil obeys an associated flow rule and the ultimate bearing capacity for the problem considered can be represented by Eqn. 20, including the slope angle (β), the footing distance to the crest (L/B), and the dimensionless parameter (cu/γB) along with the effect of footing roughness and slope surcharge (q/γB),

,,,, ucpLqHfBBBBB

βγγγ

=

(20) Where, p = average unit pressure acting on the footing, q = surcharge load, cu = undrained shear strength, H/B = 3 for all analyses, L = distance of footing from the edge of footing, B = width of footing.

Finally, results were presented in the form of design charts as shown in Table 9 considering a wide range of parameters and a procedure was also suggested for estimation of bearing capacity.

318

Table 9: Design Charts Considering Effect of Different Parameters (Shiau et al., 2011)

Effect of Dimensionless Strength Ratio (cu/γB) and Effect of Slope Angle (β)

Effect of the Footing Distance to the Crest (L/B)

Effect of the Surcharge (q/γB)

Effect of H/B

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CONCLUSION

The following conclusions were extracted from the present study: 1) All the approaches used by different researchers for the evaluation of bearing capacity of

shallow foundation on slope or near the slope have their own sets of assumptions and hence corresponding weaknesses also.

2) Some investigations show that, in case of noncohesive soils, the bearing capacity is always governed by foundation failure, while in cohesive soil the bearing capacity of the foundation is dictated by the stabilityof slope.

3) Hybrid methods (viz. combination of FE method with Limit analysis or FE method with Limit equilibrium) are giving the most satisfactory results for bearing capacity calculation.

4) The method which gives the minimum bearing capacity for shallow foundation on slope is considered for conservative design.

References

Castelli, F. and Motta, E. (2010), Bearing Capacity of Strip Footings near Slopes, Geotech. Geolog. Engg., 28(2), 187-198.

Choudhury, D. and Subba Rao, K.S. (2006), Seismic Bearing Capacity of Shallow Strip Footings Embedded in Slope, Int. J. Geomech., ASCE, 6(3), 176–184.

De Buhan, P. and Garnier, D. (1998), Three Dimensional Bearing Capacity Analysis of a Foundation near a Slope, Soils Found., JGS, 38(3), 153-163.

Georgiadis, K. (2010), Undrained Bearing Capacity of Strip Footings on Slopes, J. Geotech. Geoenv. Engg., 136(5), 677–685.

Graham, J., Andrews, M. and Shields, D.H. (1988), Stress Characteristics for Shallow Footings in Cohesionless Slope, Can. Geotech. J., 25(2), 238-249.

Hansen, J.B. (1970), A Revised and Extended Formula for Bearing Capacity, Dan. Geotech. Ins., Bulletin No. 28.

Kusakabe, O., Kimura, T. and Yamaguchi, H. (1981), Bearing Capacity of Slopes under Strip Loads on the Top Surfaces, Soils Found., JGS, 21(4), 29-40.

Meyerhof, G.G. (1957), The Ultimate Bearing Capacity of Foundations on Slopes, in Proc. 4th ICSMFE, London, England, 1, 384-386.

Narita, K. and Yamaguchi, H. (1990), Bearing Capacity Analysis of Foundations on Slopes by use of Log-Spiral Sliding Surfaces, Soils Found., JGS, 30(3), 144-152.

Saran, S., Sud, V. and Handa, S. (1989), Bearing Capacity of Footings Adjacent to Slopes, J. Geotech. Engg., ASCE, 115(4), 553–573.

Sarma, S.K. & Chen, Y.C. (1996), Bearing Capacity of Strip Footing near Sloping Ground During Earthquake, in Proc. XIth WCEE, Acapulco, Mexico, Paper No. 2078.

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Shiau, J., Merifield, R., Lyamin, A. and Sloan, S. (2011), Undrained Stability of Footings on Slopes, Int. J. Geomech., ASCE, 11(5), 381–390.

Vesic, A. S. (1975), Foundation Engineering Handbook, ed. H. F. Winterkorn and H. Y. Fang, Van Nostrand Reinhold Co., New York.

Yamamoto, K. (2010), Seismic Bearing Capacity of Shallow Foundations near Slopes using the Upper-Bound Method, Int. J. Geotech. Engg., 4(2), 255-267.

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RAFT FOUNDATIONS AT THE END OF EARLY YEARS

Prashant Garg, Harvinder Singh and J N Jha

Abstract: During the last decades, the quick growth of cities all over the world has led to a rapid increase in the number and height of high-rise and super high-rise buildings. High-rises often rest on raft foundations or sometimes, pile foundations are used to transfer the load from the superstructure to the ground, which are designed using the conventional method recommended by various design codes and regulations, where the piles take the full load from the superstructure. Recently it is increasingly recognized that the use of piles along with the raft, and in isolation also, can be used very conveniently to reduce the foundation settlement and differential settlement with considerable savings in the project cost. In this article the result from various papers have been reviewed to conclude that raft footing in isolation is ineffective to reduce the differential settlement economically and piled-raft footing is a better alternative instead for this purpose. Keywords: Raft, piled-raft, foundation, deep footing, shallow-footings.

INTRODUCTION

Foundation is the interface between the superstructure of the high-rise building and the ground. It is primarily used to transfer safely the building loads into the ground and to keep settlement within the allowable range as suggested by the various design regulations. The foundation system must be designed to ensure sufficient external stability of the entire structural system and maintain the internal load-bearing capacity of the building components through appropriate design of the components. The serviceability of the building must be guaranteed for its entire lifecycle. In practice, normally three principal types of foundation are employed to transfer the heavy loads from high-rises to the ground viz: Raft foundations, where the loads are transferred to the ground via a foundation slab; Pile foundations, where the loads from a structural system are transferred to a deeper load-bearing layers via a long column like members embedded into the soil through friction or through end bearing ; and Pile and raft foundations (PRF), where the high-rise load are transferred through the composite action of raft, and pile foundations i.e. partly by the raft and partly by the piles or diaphragm wall.

• Raft Foundation

In subsoil with good load-bearing capacity, as dense sand and gravel, un-piled raft foundation can be the most economic option for the high-rise buildings. The Trianon tower, which is almost 190m high and Main Plaza tower, 90m high, in Frankfurt are good examples, where the settlement remained under 100 mm and the tilting less than 1:800.

• Pile Foundation

Pile foundations are necessary for cases, where the subsoil near the ground surface has low load-bearing capacity or heterogeneous conditions. The entire high-rise load is transferred to the

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firm layers only by piles or diaphragm wall. In such a foundation, or so-called conventional pile foundation, the footing slab is designed not to take any load from the superstructure. According to most standards, the piles must be designed with a safety factor of 2 to 3. This requirement results in a higher number and larger length of piles, and therefore the pile foundation is considerably expensive. Conversely, the settlement of the pile foundations is unnecessarily small. The pile foundation is the most common solution employed for high-rises worldwide, especially e.g. in the US, South East Asia, or Vietnam. Foundations are predominantly founded on large-diameter bored piles, barrettes or diaphragm wall, which are sometimes driven as deep as 80-100 m into the ground to reach load-bearing layers.

• Piled-Raft Foundation

The traditional/conventional design practice for pile foundations is based on the assumption that the piles are behaving as long columns duly embedded in the soil mass, and that the entire external load is carried by the piles, with contribution of the footing being ignored. This approach is over-conservative, since the raft or pile cap is actually in direct contact with the soil, and thus carries a significant fraction of the load. The philosophy of design is recently undergoing a gradual change. The concept of piled-raft foundations, in which the load from superstructure is partly taken by piles and the remaining taken by the raft is more and more accepted. The piles are designed to reduce the settlement, not to take the total load. This idea of using piles as settlement-reducers was started in the seventies (Hansbo et al., 1973; Burland et al., 1977). In the case of piled raft on clay, this philosophy has been developed into a refined design method in Sweden. According to the design method, the building load inducing stresses in excess of the clay pre-consolidation pressure is carried by the piles in a state of creep failure, while the remaining portion of the load is carried by the contact pressure at the raft-soil interface (Hansbo, 1984; Jendeby, 1986; Hansbo & Jendeby, 1998). A similar approach was introduced in the UK by Burland (1986). Enormous contributions to the development of the piled-raft foundation concept have been done in Germany during the 80’s and 90’s of the last century. Many piled raft foundations have been constructed in the Frankfurt Clay using settlement-reducing piled foundation for heavy high-rises (Sommer et al., 1985; Katzenbach et al., 2003). There are also applications in non-cohesive soil, like the Berlin Sand (El-Mossallamy et al., 2006). Recently, super high-rise buildings in the Gulf have often been constructed upon piled rafts. The load of the buildings is shared between the piles in shaft friction and the raft in direct bearing, with the pile system typically carrying about 80% of the total load directly into the deeper strata (Davids et al., 2008). For piled footings in non-cohesive soil, a systematic experimental study of the behavior of the piled footings with the cap being in contact with the soil surface, has been carried out by the Author, Phung (1993). The study shows that the influences of the footing (cap) in contact with the soil on the bearing capacity of piles and on the load-settlement behavior of a piled footing are considerable. The mechanism of load transfer in a piled footing involves a highly complex overall interaction between piles, pile cap and surrounding soil, which is considerably changed due to pile installation and to the contact pressure at the cap-soil interface. In the paper, the results of various experimental and analytical studies are reviewed.

REVIEW OF PAST RESEARCH WORK

Meisam Rabiei (2010): In this paper effect of pile configuration and loading type on piled raft foundations performance has been studied by the authors. The parametric study presented in this research work was carried out with a computer program ELPLA. Three basic pile configurations and three load distribution types were considered and the effect of loading type for each pile

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configuration on maximum moment in the raft, piles bearing factor (percentage of total load carried by piles) and piled raft settlement was studied. Pile configuration 1 has the pile uniformly distributed under whole raft area. Pile configuration 2 has piles under central area of the raft as well as under the edges of the raft. In pile configuration 3 the piles are placed only in the central area of the raft. It has been found that pile configuration and load distribution are very important and effective in piled raft settlement, maximum moment and piles bearing factor.

Chun-yi Cui, Mao-tian Luan, and Mu-guo Li (2010): On the soft grounds, effects of consolidation on performance of the system of piled rafts as well as superstructures cannot be overlooked due to nonlinear interaction characteristics. Conventional methods of engineering design and numerical procedures of two-dimensional interaction analysis cannot realistically simulate loading and deformation mechanism of the interaction system and cannot completely predict variations of deformations and internal forces of both structure and piled raft foundation. Therefore in order to well understand long-term behavior of the interaction system, time-dependent effect of soil deformations on performance of the interaction system of piled rafts and foundations as well as superstructure is evaluated in this paper. The nonlinear deformation and strength behavior of foundation soils are taken into account by using the elasto-plastic constitutive model based on Mohr-Coulomb's yield criterion while the consolidation effect of subsoil under loading is incorporated by numerically solving the coupling Biot's equations of consolidation. Numerical analyses are conducted for the structure-raft-foundation interaction system by using the finite element methods. Based on numerical analyses for a given interaction system, both the features of variation in time of internal forces, settlements and the characteristics of compatibility mechanism of interaction system are examined. It is shown that both nonlinear behavior of soft soils and consolidation characteristics of foundation remarkably affect the time-dependent performance

Kiyoshi Yamashita, Junji Hamada, and Yutaka Soga (2010): This paper presents a case history of design and performance of a piled raft supporting a 162 m high residential tower. The 47-story building is a reinforced concrete structure and the average contact pressure over the raft is 600 kPa. The raft is founded on diluvial sand-and-gravel at a depth of 4.3 m below ground surface. Because the building has a base isolation system, differential settlement of the foundation is rigorously restricted. To reduce the differential settlement, a piled raft foundation consisting of thirty-six 50-m long cast-in-place concrete piles was adopted. To confirm the validity of the foundation design, field measurements were performed on the settlement of the foundation, axial loads of the piles, contact pressures between raft and soil and pore-water pressure beneath the raft from the beginning of construction to eight months after the end of construction. Based on the field measurement results, the foundation design was found to be appropriate.

S. N. Moghaddas Tafreshi (2010): In this paper, nonlinear pile-soil-structure interaction under dynamic loads has been formulated by using free-field soil analysis and beam on Winkler foundation. The free-field motions are calculated separately through a site response analysis using DYFRA program which was developed by the author to prepare the data in the form of displacement time history. Linear beam column finite elements are used to model the piles and structural elements. Nonlinear modeling of soil media is done by introducing a rational approximation to continuum with nonlinear interface springs along the piles. In order to calibrate the parameters used in the model and also verify the proposed formulation, the result of a shaking table tests are used. The numerical analyses-show good consistency with the test results, in terms of recorded spectral acceleration of soil layers and acceleration time history of superstructures above the piles.

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Y. F. Leung, A. Klar, Ph.D., and K. Soga, Ph.D., (2010): Pile groups are frequently designed with equal or similar pile lengths. However, the significant interaction effects among equal-length piles imply that this may not be the optimized configuration. This paper presents the optimization analyses of piled rafts and freestanding pile groups, where pile lengths are varied across the group to optimize the overall foundation performance. The results of the analyses are applicable in cases where the piles derive a majority of the capacity from the frictional resistance. It is demonstrated that, with the same amount of total pile material, an optimized pile length configuration can both increase the overall stiffness of the foundation and reduce the differential settlements that may cause distortion and cracking of the superstructure. The benefits of the optimization can be translated to economic and environmental savings as less material is required to attain the required level of foundation performances. The reliability of the optimization benefits in relation to construction-induced variability is also discussed.

Ron Xia, Vladimir Dolezel, L. Rak, H. Qian, and B. Rao (2009): The paper describes the design of a Partially Piled Raft Foundation (PPRF) adopted under complex geotechnical conditions, in the City of Toronto, Canada. The design of PPRF was governed by lateral soil pressure, unevenly distributed building loads, and non-uniform bearing capacity of foundation soils. Piles were distributed in the area with excessive settlement. Most of the supporting piles were located in the northwest portion of the raft foundation, where high bearing pressure and low soil bearing capacity were encountered. A unit criterion of the proposed settlement has been applied in the design of the raft slab and the piles in order to keep the integrity of the PPRF. Global stability, including sliding and over turning of the PPRF were an integral part of the design. A state of the art computer analysis was utilized.

Juan M. Mayoral, Miguel P. Romo, and Sergio Martinez (2008): Seismic soil-structure interaction performance evaluations of projects located in deep soft clay deposits warrant special attention, particularly when designing strategic infrastructure that must remain operating after a major earthquake. The development of numerical analytical platforms in recent decades, along with faster computing tools, have made possible to include in the state of practice quite sophisticated solution techniques aimed at better representing the physics of the problem at hand. This paper presents the application of a 3-D finite difference model for evaluating the static and dynamic response of a 118 by 100 m cellular-raft foundation to be built in soft clay. The raft foundation is a 2.5 m high box-type foundation embedded 1 m and supported by a grid of peripheral and internal walls, 2.5 m long and 0.40 m thick, which integrates a cellular structure. The model is used to obtain first the static behavior exhibited by the foundation for the construction stages, including long term consolidation, and then the design earthquake is considered and the equation of motion is solved in time domain.

Vincenzo Fioravante, Daniela Giretti, and Michele Jamiolkowski (2008): The paper presents the results of extensive centrifuge tests modeling rigid circular piled rafts laying on a bed of loose very fine silica sand. The tests were aimed at investigating the behavior of rafts on settlement reducing piles. The testing program included: an unpiled raft, rafts on 1, 3, 7 and 13 piles. In each test, some model piles were instrumented with load cells to determine the distribution of load along the shaft. Beneath the rafts, two types of model piles, close-ended and free headed were installed: quasi displacement (QD) and quasi-non displacement (QND) piles. The obtained results permitted figuring out the role of piles in terms of their effectiveness as settlement reducers and to quantify the load sharing mechanism between piles and the raft-soil contact. The tests were aimed at investigating the load transfer mechanisms adopted in the design approach, and in particular at validating a numerical code which can be used in engineering

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practice. The paper describes the details of experiments undertaken, the adopted procedures and some of the results; where not specified, all the experimental data given in this paper referred to model scale. The adopted numerical code is briefly described and its validation, via test results on quasi-non displacement piles, is also reported.

J. C. Small and H. G. Poulos (2007): A method of analysis has been presented for piled raft foundations where the piles exhibit non linear load-deflection behaviour. The raft is analysed through the use of finite element methods, while the piles are treated as springs having a variable stiffness, so as to model any non-linear behaviour. The soil is treated as an elastic medium that may consist of layers of soil having different stiffnesses. Interaction between the piles in the group is assumed to remain constant even though the stiffness of the piles may change with load level. The method has been incorporated into the computer program GARP (General Analysis of Rafts with Piles). This program is used to analyse a tall building that was constructed on a piled raft foundation, and a comparison is made of the calculated and observed behaviour.

F. Liang, J. Li, and L. Chen (2006): The authors have studied how to achieve optimization of a piled raft foundation with varied cushion rigidity. The analysis model of piled raft foundation was set up using the fictitious pile method, and Fredholm's integral equations of the second kind were deduced to solve the problems. By simulating the cushion with Winkler springs, the effect of cushion was taken into consideration. The present method is suitable to analyze the foundation under working loads and could be applied to solve problems of different rigidities of piles and cushion. By adjusting the cushion's rigidity, the optimizing goal could be reached. Numerical examples are presented to illustrate the design principles.

F. Garcia, A. Lizcano and O. Reul (2006): In the paper, authors has studied one case history of a piled raft foundation, Messeturm tower in Frankfurt Germany using a viscohypoplastic constitutive law in a three dimensional finite element analysis with the program ABAQUS and the user subroutine UMAT. In the finite element analysis the construction process of the Messeturm tower has been modelled. The calculated results are compared with the in situ measurements with the purpose to verify the viscohypoplastic law in a boundary value problem.

Y. C. Tan, S. W. Cheah, and M. R. Taha (2006): Conventional piled foundation is usually designed to provide adequate load carrying capacity for buildings and to limit the overall settlement and to control differential settlement within tolerable limits. Conventionally, piles are often installed into competent stratum or to `set'. However, this solution generally only addresses the short-term problem associated with soft clay as pile capacity will be significantly reduced due to negative skin friction. This often reduces the cost-effectiveness of such `conventional solution'. In this paper, the design methodology of a `floating' piled raft foundation system for medium rise buildings (5-story) on very soft clay has been discussed. The main design objective is to control differential settlement at the onset rather than only limiting the overall settlement. The piled raft foundation of the said medium rise building is designed using skin-friction piles of varying length. The design also considers the interaction between the piled raft and soil in order to produce an optimum design which satisfies both serviceability and ultimate limit states. The design methodology and monitoring results of the successfully implemented piled raft foundation for medium rise building are also presented in the paper.

L. G. Vásquez, S. T. Wang, and W. M. Isenhower (2006): A variational approach for the analysis of piled raft foundations is presented. The raft and piles are both analyzed by the use of the principle of minimum potential energy. By representing the deformation of the piles and raft

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using finite series, the method is very efficient for the analysis of a piled raft with a large number of piles. Comparisons with other numerical methods and field measurements have shown reasonable agreement.

Luca de Sanctis and Alessandro Mandolini (2006): The conventional design of a piled foundation is based on a bearing capacity approach, and neglects the contribution of the raft. As a consequence, piled foundations are usually designed by overconservative criteria. With respect to the conventional approach, a more rational and economical solution could be obtained by accounting for the contribution of the raft toward the overall bearing capacity, but this potential is not exploited due to the lack of theoretical and experimental research on the behavior of piled rafts at failure. Based on both experimental evidence and three-dimensional finite element analyses, a simple criterion is proposed to evaluate the ultimate vertical load of a piled raft as a function of its component capacities, which can be simply evaluated by the conventional bearing capacity theories. The results presented in the paper thus provide a guide to assess the safety factor of a vertically loaded piled raft.

H. S. W. Chow and J. C. Small, (2006): The use of piled raft foundations has become popular in recent years as the system can act as a settlement reducer. When the raft is subjected to non-uniform loadings, piles of different diameters and lengths may be required to prevent the foundation from rotating and to reduce the differential settlement. This paper presents a finite layer method used for the analysis of piled rafts with piles of different lengths and diameters. The soil is divided into horizontal layers with different material properties and only vertical loads may be applied to the raft. Interactions between raft-soil-pile are computed. Results from the present method are shown to agree closely with those from the finite element method.

Lisa J. Novak, Lymon C. Reese, Hon.M.ASCE; and Shin-Tower Wang (2005): One of the most challenging problems in soil-structure interaction is the piled raft. Piled-raft foundations for important high-rise buildings have proved to be a viable alternative to conventional pile foundations or mat foundations. The concept of using piled raft foundation is that the combined foundation is able to support the applied axial loading with an appropriate factor of safety and that the settlement of the combined foundation at working load is tolerable. In some instances the piles are spaced uniformly and in other cases are spaced strategically to achieve a more uniform settlement of the mat. Two strong reasons dictate the use of the 3D Finite Element Method (FEM): (1) the problem is so complex that simplified methods cannot model the problem correctly; and (2) codes for the FEM are available, powerful, and capable of being run on the personal computer. Thus, the modeling of the raft, piles, and supporting soil as a soil-structure-interaction problem using FEM is a feasible method. Two piled-raft foundations were analyzed using the FEM program. Comparisons were made between experimental and analytical results and the FEM was shown to yield excellent results for the cases analyzed.

Harry G. Poulos (2005): This paper re-visits the compensated piled raft foundation system, and outlines a simplified approach to the analysis of both conventional piled rafts and compensated piled raft foundations for the support of structures on very soft clays. Two cases are considered: the first where only applied load acts on the foundation, and the second where both applied load and externally imposed ground settlements act. It is demonstrated that the use of compensation, via excavation of the soil and embedment of the raft, can lead to significant reductions in settlement compared to normal (uncompensated) piled rafts. Importantly, when ground settlements occur, the use of compensated piled rafts can lead to significantly reduced differential settlements between the structure and the ground, compared to the case where the

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structure is supported by end bearing piles. Indeed, the latter may be counter-productive and lead to the not uncommon situation where the building stands well above the surrounding ground. A simplified design approach is proposed, and it is demonstrated that this simplified approach can lead to a computed behavior which is consistent with past experience in Mexico City.

Oliver Reul (2004): Based on a numerical study by means of three-dimensional finite-element analysis, this paper discusses investigations of the bearing behavior of piled rafts in overconsolidated clay. It is shown that the interaction between piles and rafts is a major influence. The potential savings of an optimized foundation design are demonstrated for a simple example.

Luca de Sanctis and Gianpiero Russo (2003): In this paper the main criteria adopted for the design and some aspects of the observed behavior of the piled foundations of a cluster of circular steel tanks are reported. They were designed to store sodium hydroxide, a toxic liquid with a unit weight of 15.1 kN/m3. Shallow foundations would have been safe against a bearing capacity failure, while the predicted settlement was beyond the allowed limit. Accordingly piles were designed to reduce the settlement and improve the overall performance of the foundations. While conventional capacity based design approach led to a total of 160 piles to support the five tanks the settlement based design approach led to a total of 65 piles achieving significant savings on the cost of the project. The settlements of four out of the five tanks were measured and for two out of the five tanks the load sharing among the raft and the piles was also observed. Both the analyses carried out at the design stage and the back-analyses of the observed behavior were based on the interaction factors method as implemented in the computer code NAPRA

H. G. Poulos (2002): This paper outlines the development of a simplified method of analysis which can provide a useful tool for preliminary design of piled raft foundations. It involves two phases: 1) The assessment of the overall foundation behavior and 2) The assessment of the behavior under individual column loads. In both cases, use is made of simplified solutions to compute foundation stiffness and capacity characteristics. The selection of design geotechnical parameters is an essential component of both design stages, and some approximations for estimating the necessary parameters are summarized. Typical applications to a case history of a piled raft and to model centrifuge tests has been described, and it is found that the behavior predicted by the simplified analysis is broadly consistent with the measured behavior.

Yasser El-Mossallamy (2002): The piled raft foundation has shown its validity in the last two decades as a very economic geotechnical foundation type, where the structural loads are carried partly by the piles and partly by the raft contact stresses. The structural serviceability requirements regarding the settlements and tiltings of buildings can be fulfilled with relatively fewer piles in comparison with a pure piled foundation. This foundation system was successfully applied in stiff as well as soft subsoil. An innovative application of the piled raft is its special adjustment to cases of foundations with large load eccentricities or very different loaded parts of buildings to avoid the need of complex settlement joints especially below ground water table. Extensive measurements of the load transfer mechanism of piled raft foundations during and after the construction were performed to verify the design concept and to prove the serviceability requirements. Calculation procedures to model the behavior of such complex three-dimensional problems have been developed since the 1970s. But some important requirements concerning the raft stiffness, the nonlinear behavior of the pile support and the slip developing along the pile shafts even under working loads were not sufficiently considered in these analyses. For these reasons an improved numerical model based on a mixed technique of the Finite Element Method (FEM) and the Boundary Element Method (BEM) was developed taking into account all above

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mentioned effects. The results of measurements and of the developed calculation method will be shown and compared in a short overview.

J. C. Small and H. H. Zhang (2002): This article presents a new method of analysis of piled raft foundations in contact with the soil surface. The soil is divided into multiple horizontal layers depending on the accuracy of solution required and each layer may have different material properties. The raft is modelled as a thin plate and the piles as elastic beams. Finite layer theory is employed to analyze the layered soil while finite element theory is used to analyze the raft and piles. The piled raft can be subjected to both loads and moments in any direction. Comparisons show that the results from the present method agree closely with those from the finite element method. A parametric study for piled raft foundations subjected to either vertical or horizontal loading is also presented.

B. M. El-Garhy, W. K. Wray, F. and A. A. Youssef (2000): This paper describes the development of a two-dimensional soil-structure interaction model based on the finite element method for calculating the structural design parameters (i.e., moments, shears, and deflections) in a raft foundation (stiffened or constant thickness) resting on expansive soil. The model is capable of estimating the distorted mound shape by considering the soil suction distribution differences throughout the supporting soil mass and the associated volume changes (shrink/heave) with respect to time under a set of different edge conditions. The model requires only a statement of the initial soil suction conditions in the supporting expansive soil mass and the changes in the boundary conditions to predict the response of the raft foundation to these boundary condition changes. The model has been shown to yield results that agree well with reported field measurements of surface volume changes (shrink/heave).

CONCLUSION

It was observed that lot of work is being done in India and abroad on design concept of piled raft foundation as it is most economical specially for tall structure but still lot of work need to be done as simple design empirical or theoretical formula or design chart is not available.

References

F. Garcia,1 A. Lizcano,2 and O. Reul3 (2006) ” Viscohypoplastic Model Applied to the Case History of Piled Raft Foundation” GeoCongress 2006: Geotechnical Engineering in the Information Technology Age,Proceedings of GeoCongress 2006

H. G. Poulos (2002) “Simplified Design Procedure for Piled Raft Foundations” In the Proceedings of the International Deep Foundations Congress 2002 Yasser El-Mossallamy (2002) “Innovative Application of Piled Raft Foundation in Stiff and Soft

Subsoil” in Proceedings of the International Deep Foundations Congress 2002 4. J. C. Small and H. G. Poulos (2007) “Non-Linear Analysis of Piled Raft Foundations” in the

Proceedings of Sessions of Geo-Denver 2007 F. Liang, J. Li, and L. Chen (2006): “Optimization of Composite Piled Raft Foundation with Varied

Rigidity of Cushion” in the Proceedings of Sessions of GeoShanghai 2006 Meisam Rabiei (2010) “Effect of Pile Configuration and Load Type on Piled Raft Foundations

Performance” in the Proceedings of the 2010 GeoShanghai International Conference J. C. Small and H. H. Zhang (2002): “Behavior of Piled Raft Foundations Under Lateral and Vertical Loading” Int. J. Geomech. Volume 2, Issue 1, pp. 29-45 (January 2002) Ron Xia, Vladimir Dolezel, L. Rak, H. Qian, and B. Rao (2009) “Geotechnical Design of a Partially

Piled Raft Foundation” in the Proceedings of selected papers of the 2009 International Foundation Congress and Equipment Expo

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Harry G. Poulos (2005) “Piled Raft and Compensated Piled Raft Foundations for Soft Soil Sites” in the Proceedings of the Sessions of the Geo-Frontiers 2005 Congress

B. M. El-Garhy, W. K. Wray, F. and A. A. Youssef (2000) “Using Soil Diffusion to Design Raft Foundation on Expansive Soils” in the Proceedings of Sessions of Geo-Denver 2000

Y. C. Tan, S. W. Cheah, and M. R. Taha(2006): “Methodology for Design of Piled Raft for 5-Story Buildings on Very Soft Clay” in the Proceedings of Sessions of GeoShanghai 2006

L. G. Vásquez, S. T. Wang, and W. M. Isenhower (2006): “Estimation of the Capacity of Pile-Raft Foundations by Three-Dimensional Non-Linear Finite Element Analysis” in the Proceedings of GeoCongress 2006

Y. K. Chow, K. Y. Yong, and W. Y. Shen (2001): “Analysis of Piled Raft Foundations Using a Variational Approach” Int. J. Geomech. Volume 1, Issue 2, pp. 129-147 (April 2001)

Chun-yi Cui, Mao-tian Luan, and Mu-guo Li (2010): “A Study on Time-Effects of Piled Raft System by Using Computational Methods” in the Proceedings of the 2010 GeoShanghai International Conference

Kiyoshi Yamashita, Junji Hamada, and Yutaka Soga (2010): “Settlement and Load Sharing of Piled Raft of a 162 m High Residential Tower” in the Proceedings of the 2010 GeoShanghai International Conference

S. N. Moghaddas Tafreshi (2010): “Numerical Simulation of Pile-Soil-Structure Interaction under Dynamic Loading” in the Proceedings of the 2010 GeoShanghai International Conference

Y. F. Leung, A. Klar, Ph.D., and K. Soga, Ph.D., (2010):” Theoretical Study on Pile Length Optimization of Pile Groups and Piled Rafts” J. Geotech. and Geoenvir. Engrg. Volume 136, Issue 2, pp. 319-330 (February 2010)

Luca de Sanctis and Gianpiero Russo (2008): “Analysis and Performance of Piled Rafts Designed Using Innovative Criteria” J. Geotech. and Geoenvir. Engrg. Volume 134, Issue 8, pp. 1118-1128 (August 2008)

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USE OF TIRE SHREDS IN REDUCING EARTH PRESSURE ON EARTH-RETAINING

STRUCTURES

S. Bali Reddy and A. Murali Krishna Department of Civil Engineering, Indian Institute of Technology, Guwahati 781039, India.

Abstract: Earth-retaining structures play important role in the various infrastructure projects and for the urban development. These structures will be subjected to various types of loading including the seismic loading under earthquake conditions. Among various parameters that need to be considered in the design of retaining structures, lateral earth pressures resulting from the supported backfill are the most predominant and the same is the influencing parameter on the performance of the structure under variety of loading conditions. With the efforts of reducing the earth pressure on the retaining structures, lightweight materials came into practice that is effectively serve the purpose. This paper reviews the use tire shreds behind earth retaining backfill material.

Keywords: Retaining Structures, Earth pressures, Shred tire.

INTRODUCTION

In national planers of India is given priority of infrastructures development and also urban development. Among these, earth retaining structures are playing an important role. Lateral earth pressure theory is for the design of ground engineering structures such as retaining walls, basements, tunnels. If lateral earth pressures are more the earth retaining structures may fail. With the efforts of reducing the earth pressure on the retaining structures by using light weight material. Scrap tires that have been cut into chips are coarse grained, free draining, and have a low compacted density (Humphrey et al. 2007). Tire chips are extensively used as a light weight backfill material in earth retaining structures.

• Scrapped tires or Tire chips

Tire chips or Tire shreds and Scrapped tires are lightweight materials used in geotechnical applications like behind the earth retaining structures, embankments etc. and also tire chips mixed with sand used as a backfill material on earth retaining structures in various U.S. states and outside the U.S.A. (Bosscher et al. 1997; Humphrey 1996; Humphrey et al. 2000, Dickson et al. 2001; Zornberg et al. 2004). The specific gravity of tire shreds ranges from 1.02 to 1.36, depending on the amount of glass belting or steel wire in the tire (Edil and Bosscher 1994; ASTM 1998). The specific gravity of soils typically ranges from 2.6 to 2.8, which is more than twice that of tire shreds (Reddy and Marella 2001). The unit weight of different types of compacted tire shreds, as reported in the literature, ranges from 2.4 to 7.0 kN/m3 (Humphrey and Manion 1992; Ahmed 1993; Ahmed and Lovell 1992; Humphrey et al. 1993). These values are approximately 0.1-0.4 times the unit weight of typical soils. Scrap tires and their by-products are not biodegradable, not

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expensive, high elastic compressibility. Tire shreds are free draining. The typical field application of scrap tire showed Figs.1

Cecich et al. 1996 conducted different laboratory tests by using shredded tires with mixing sands. Using these properties, retaining wall of various heights were also designed using shredded tires as the backfill material and also designed by considering sand for comparison purposes.

Fig. 1.Typical Field Application of Scrap tire (after Kazuya Yasuhara, 2007)

Table.1 shows comparison of factor of safeties with sand, shredded tire backfill material. It was concluded that, both sliding and overturning factor of safety for the retaining walls with shredded tires were significantly more than that for use of the sand as a backfill material. And cost estimate with different height of walls and backfill materials sand and shredded tires used. Based on observations, the total construction cost saving is 67%.

Table.1 Comparison of factor of safety for retaining walls with sand vs. shredded tires as backfill materials (100 ft long walls)

Height of wall (ft) Sliding factor of safety Overturning factor of safety

Sand Shredded tire Sand Shredded tire 10 4.15 >20 2.10 >20 20 1.68 10.37 1.84 2.12 30 1.54 3.35 1.65 2.14

Hazarika et al. 2006 conducted two series of tests. In one series only sand backfill (case A)and second series sand and tire chips (case B) as shown in Fig.2. The range of grain size tire-chips 4mm to 40mm used in the test. The dynamic earth pressures at maximum inertia force are plotted against the wall height in Fig.3. It reported distribution for backfill without any tire-chips (cushion) shows a nonlinear increase of the earth pressure with the wall depth. However, distribution for the backfill with cushion shows a maximum increase in the middle of the caisson height, and then a gradual decrease.

Lee et al.2007 studied the effects of the compressible materials on the stress variation with soil depth in the backfill of retaining walls. In the study two compressible materials (recycled tire and Geofoam) were used. In the sensitivity analysis, elastic modulus values are varying. Elastic modulus was determined based on the stiffness ratio and stiffness ratio defined as (RE=E cushion

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/E backfill). From the results presented in Table.2, it was observed that, the dynamic earth pressure and total earth pressure decrease when stiffness ratio decreases

Fig. 2: Typical application of Tire-chips

Table.2: Comparison of peak horizontal earth pressures obtained from numerical and field experiments (after Lee et al., 2007)

Cushion type EPS Tire

Elastic modulus 9387 1400

Numerical Analysis

With cushion 87 41

Without cushion 138 143

% Reduction 37 71

Filed test With cushion 10 9

Without cushion 13 30

% Reduction 23 70

Tanchaisawat et al.2008 reported by the maximum lateral wall movement of the lightweight

embankment at the top was 45% lower when compared to the corresponding conventional sand embankment.

Nakhaee et al. (2011) conducted different tests by using different percentages of rubber inclusion and also the particle size distribution for granular soil and granulated rubber shown in fig.3. Finally it reported by the maximum horizontal pressure applied to the wall decreased with an increase in rubber percentage shown in figures 4 and 5.

Fig.4 Maximum Horizontal Pressure Values Applied on the Wall for Different Percentages in the

EL Centro Earthquake

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Fig.5 Maximum Horizontal Pressure Values Applied on the Wall for Different Percentages in the

Tabas Earthquake

CONCLUSIONS

Lateral earth pressures acting on retaining walls are the main concern in the design and stability aspects of retaining structures. In the efforts to minimising earth pressures on retaining walls, use of Tire-chips or Scarp tires. Some of the researchers are being involved in investigating the effectiveness and possibility of using this material in the retaining wall applications. Some of such studies on waste tire and their derived materials were presented briefly in this paper. Further more studies are essential to derive guidelines for using novel materials (i.e. light weight materials and compressible inclusion materials) in retaining wall application of geotechnical engineering.

Reference Ahmed, I., and Lovell, C.W. (1992). "Use of waste productsin highway construction." Environmental

geotechnology. Balkema, Rotterdam, 409-418. Ahmed, I. (1993). Laboratory study on properties of rubber soils. Report No. FHWA/IN/JHRP-93/4,

Purdue University, West Lafayette, Indianapolis. Bosscher, P.J., Edil, T.B., and Kuraoka, S. (1997). "Design of highway embankments using tire chips."

Journal of Geotechnical and Geoenvironmental Engineering, ASCE, 123(4), 295-304. Cecich V. et.al.,(1996), Use of Shredded Tires as Lightweight Backfill Material for Retaining

Structures, Waste Management & Research (14),433-451. Dickson, T.H., Dwyer, D.F., and Humphrey, D.N.(2001). "Prototypes tire-shred embankment

construction." Transportation Research Record 1755, TRB, National Research Council, Washington, D.C., 160-167.

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Earthquake Resistance of Structures using Tire Chips as Compressible Inclusion”, Report of the Port and Airport research institute. Vol.45, No.1.

Humphrey, D.N., Whetten, N., Weaver, J., Recker, K., and Cosgrove, T.A. (1998). "Tire TDA as lightweight fill for embankments and retaining walls." Proc., Conference on Recycled Materials in Geotechnical Application, Arlington, Virginia, ASCE, 51-65.

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Humphrey, D.N., and Kate, L.E. (2000). "Five year study of the effect of tire TDA placed above the water table on groundwater quality." Transportation Research Record 1714, Transportation Research Board, Washington, D.C., 18-24.

Humphrey, D.N. (2007). "Tire-derived aggregate as lightweight fill for embankments and retaining walls." Proc., International Workshop on Scrap Tire Derived Geomaterials-Opportunities and Challenges (IW-TDGM 2007), Yokusuka, Japan.

Kazuya Yasuhara (2007), Recent Japanese experiences on scrapped tires for geotechnical applications, proceedings of the international workshop on scrap tire derived geomaterials– opportunities and challenges, Yokosuka, Japan.19-42.

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Nakhaee and S. M. Marandi (2011) “Reducing the Forces Caused by Earthquake on Retaining Walls using Granulated Rubber-Soil Mixture”, IJE Transactions B, Vol. 24, No. 4,337-350.

Reddy, K., and Marella, A. (2001). "Properties of different size scrap tire shreds: implications on using as drainage material in landfill cover systems." Proc., 7th International Conference on Solid Waste Technology and Management, Philadelphia, 1-19.

Tanchaisawat et al. (2008). “Performance of full scale test embankment with reinforced lightweight geomaterials on soft ground”, Lowland Technology International Vol.10, No. 1, 84-92.

Zornberg, J.G., Alexandre, R.C., and Viratjandr, C. (2004). "Behaviour of tire shred-sand mixtures." Canadian Geotechnical Journal, 41(2), 227-241.

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MUNICIPAL SOLID WASTE MANAGEMENT IN GOA – A CASE STUDY

M. Anawkar*, S. Sheikh* and P. Savoikar** *Civil Engineering Student, Goa Engineering College, Farmagudi, Goa, India.

** Head of Civil Engineering Department, Government Polytechnic, Bicholim, Goa, India.

Abstract: This paper discusses about municipal solid waste management in two major cities in the State of Goa viz. Panaji, the capital city and Ponda where the problem of municipal solid waste management is alarming. About 20-25 tonnes of solid waste in generated in these two cities collectively. Management of this waste is a big challenge since proper disposal method for this waste is not yet in place. The waste collected is being separated into biodegradable and non-biodegradable waste. Separate bins are also provided to collect plastics, glass, etc. Few composting units and organic waste composter are used to handle this waste but are insufficient. Of late suitable site is being identified for municipal solid waste landfill, but still under planning stage. This paper discusses various options of collecting waste, composting and utilization of plastic waste collected in proper manner. Recycling and other methods are also suggested so that load on landfill is reduced. Presently, plastic waste is palletized and sent to cement companies outside Goa. This paper also suggests various recycling techniques. Important of them are, use of plastic waste in roads and also in concrete as partial replacement of sand. This alternative is suggested since sand mining in Goa is controlled and supply of sand from neighboring States is also stopped. Various environment friendly techniques which can be easily implemented are discussed here.

INTRODUCTION With rapid strides in urbanization, modernization and industrialization, human beings are introduced to variety of problems of which prominent is solid waste management. Use of plastics have found a vital role in day to day life and has practically replaced standard materials like steel, wood and paper which are otherwise less harmful and do not cause much of pollution. However, due to its versatile properties like strength, mouldability into any shape, attractiveness, light weight and low cost, plastics are used in abundance and in many a cases disposed off after single use. This has lead to huge growth in municipal solid waste all over the world. Failure in proper management of this waste has lead to several health hazards and accumulation of waste in cities and towns totally changing the façade of these cities in addition to foul smells and related health hazards. Of late, municipal solid waste is collected and disposed off in municipal solid waste landfills which need to be maintained properly and closed once desired height or volume is reached. This process however, has taken up huge space of land which is a costly resource in these cities. Hence, a solution needs to be found which will reduce generation of the waste or will reduce the amount of the waste going into the landfill. In the present paper, study of the waste generated from an urban city, Panaji, the capital city of Goa and Ponda, a sub-urban town located in Goa’s heartland is presented along with possible solutions.

SOLID WASTE MANAGEMENT IN PONDA

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In Ponda city, approximately 6 to 7 tons of solid waste is generated on daily basis, of which 65% is wet waste (biodegradable) and the remaining is dry waste (non-biodegradable). The methods of collection of waste are mainly door-to-door collection, i.e. collected on alternate days and also collection from various bins located at strategic points. The other method of collection is by the use of Compactor trucks having net capacity of 2-3 tons. Out of the total waste generated, nearly 50% of it is segregated at source and the remaining part is separated manually. There exits an acute shortage of a proper site for the disposal of this waste. Part of the biodegradable waste (wet waste) is sold to the nearby farms as organic manure and the remaining biodegradable waste is sent for Vermicomposting. Vermicomposting is presently carried out at five sites. In this method 3 chambers are loaded at a time and left for composting for a period for 30 days. Table 1 shows the various vermicomposting sites in Ponda and their composting capacities.

Table 1: Vermicomposting sites in Ponda, Goa

Location of Site Composting Capacity (cubic meter) Govt. Primary School, Khandepar 9.79

Yashwantnagar 8.64 Behind Sadhale house 7.83

Upper Bazaar 13.36 Shantinagar 3.51

Total 43.13

The non-biodegradable waste is stacked in plastic bags and is sold off to cement companies. The Ponda Municipality highlighted that the major problems faced in disposing the generated solid waste was the unavailability of a suitable site for dumping and shortage of facilities to do the same. The Municipality also faces acute labour and vehicle shortages. Presently, a team of 40 labours and two trucks manage the collection on entire waste in the city. Figure 1 (a) shows the non-biodegradable waste collected in plastic bags and (b) shows indiscriminate throwing of plastic waste in open areas in the city. Figure 2 shows the trucks utilized for transporting of waste.

METHODOLOGY ADOPTED AT PONDA In order to deal with the solid waste management issue, the Municipality has proposed to install a waste management plant having a processing capacity of 30 tons per day. The waste processing steps are shown in the flowchart in Figure 3. The waste processing consists of dumping the waste generated into a machine called Windrose which dries the waste. Then the waste is put into a Tromel which segregates the waste as wet or dry. Then the processed wet waste is sent for composting. The dry waste is further divided into inert or recyclable waste. The inert waste is sent to a scientific landfill (a site 16,000 m2 has been identified in Kariyan, Khandepar) and the recyclable waste is sold.

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(a) (b)

Fig 1: (a) Non-biodegradable Waste Stacked in Plastic Bags, (b) Indiscriminate Throwing of Plastic Waste in Open Areas

Fig 2: Equipment Used for Waste Collection

Fig 3: Flowchart Showing Waste Processing Steps

MUNICIPAL SOLID WASTE MANAGEMENT IN PANAJI CITY In Panaji city, approximately 12 to 13 tons of solid waste is generated per day. Nearly 60% of this waste is wet waste (biodegradable) and the remaining 40% waste is dry waste (non-biodegradable). The method of collection of waste is mainly door-to-door collection. Wet-waste is

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collected everyday while dry-waste is collected on Mondays and Thursdays. At every household, two bins are maintained, green bin for wet-waste and black bin for dry-waste. Waste from restaurents/hotels is collected separately twice a day. The hotel waste is segregated in four color coded bins, orange for plastics, purple/pink for non-recyclable materials, black/grey for glass and metals and brown bins for papers and cartons. The other method of collection is by the use of compactor trucks (4 nos.) having capacity 7 m3 and Dumper trucks (7 nos.) having capacity of 8-9 m3. The waste if not segregated at source is segregated at Patto, Panjim. Figure 4 shows colour coded bins used at Panaji city.

Fig 4: Various Color Coded Segregation Bins

METHODOLOGY ADOPTED AT PANAJI

The segregated biodegradable waste is sent for Vermicomposting as in case of Ponda city. The vegetable waste generated from the market is treated in the market itself while the fish/meat waste is sent for segregation at Patto, Panaji. The non-biodegradable waste is segregated as chips and bottles and is sold at different prices. Some of the plastic waste is sold to cement factories in the form of compressed bails. Table 2 shows the details of composting units installed in the Panaji city.

The Panaji Municipality highlighted that the major problems faced in disposing the generated solid waste was the unavailability of a suitable site for dumping and shortage of facilities to process the waste. Previously a small landfill was used at Campal but a large scale solution is required. Hence, the municipality has identified the land at Baiginium, Curca but it is still in the proposal stage.

Table 2: Details of Composting units as per number of dwelling units

Sr. No.

No. of dwelling units Size 1 10-25 units 3.00 m X 1.50 m (single units) 2 26-50 units 3.00 m X 1.50 m (double units) 3 51-75 units 3.00 m X 1.50 m (3 units)

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4 76-100 units 3.00 m X 1.50 m (4 units) 5 100 and above Suitable treatment facility

Note: Each unit comprises of two compartments with standard details and specification such as seepage-proof floor and walls, covered shed, lecheate outlet pipe, inspection chambers, soak pit etc.

PROBLEMS ENCOUNTERED IN WASTE MANAGEMENT IN PONDA AND PANAJI

Municipal solid waste generated in the cities of Ponda and Panaji is collected and separated into biodegradable and non-biodegradable waste. Few composting units and organic waste composter are installed in the city to handle this waste but are insufficient. The separated plastic waste is palletized and sent to cement companies outside Goa. But the complete solution to the waste management problem is not yet in sight. There are no engineered landfills yet constructed and operated to handle the municipal waste. In addition, the State generates 4950 kg of medical waste per day, which is presently being sent to Goa Medical College for treatment and disposal. A hydroclave is purchased by the Government to handle this medical waste but is yet to be commissioned. Of late, suitable site is being identified for construction of municipal solid waste landfill, but still under planning stage. Huge piles of plastic waste comprising of PET bottles, carry bags are seen many places within these cities. Still proper facilities are required for handling non-biodegradable waste, plastic waste and medical waste. Following are some of the alternative technologies which can be resorted to solve the above problems.

• 4R’s of Waste Management: Reduce/Reuse/Recycle/Recover

One of the possible solutions for effective municipal solid waste management is minimization of the waste. This can be done by practicing the 4R’s of waste management i.e. REDUCE – reduce consumption of materials like plastics which constitutes major and problematic component of municipal solid waste; REUSE - utilize reused materials before sending them to landfills, RECYCLE - recycling of certain items in wastes so that pressure on landfills is reduced, RECOVER – important items can be recovered from waste and reused/recycled. Plastics are the major component which needs to be recycled since they will interfere with the biodegradation process in the landfills. Recycling of plastics is essentially a three stage process involving selection the waste/scrap which is suitable for recycling/reprocessing, segregation of the plastics waste as per the Indian Standards Code IS: 14534:1998 and processing the waste by washing, shredding agglomerating, extruding and then converting into granules. Recycling was reported to be one of the important methods of reducing adverse impact of plastic on the environment (Hopewell et al., 2009). It is found to reduce the quantity of waste thrown in open areas and reduce the use of oil and emission of carbon dioxide.

• Management of Plastic Wastes to Reduce Load on the Landfills

Various techniques of handling plastic are available which can be resorted to which can be economically viable also. Since plastic is known to be non-biodegradable and requires very long period to degrade which can be in the range of 1000 years, it is very important to handle plastic waste first and then to design landfills accordingly. Some of the techniques of plastic waste management include:

• Polymer coated bituminous road

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Central Pollution Control Board in collaboration with Thiagarajar College of Engineering Madurai has developed this technique which uses plastic waste in bituminous roads. It was noticed that the entire road was having good skid resistance and texture values. All the stretches in the roads were found to be reasonably strong with very good surface evenness. Also, the plastic tar roads constructed using above technology have not developed any potholes even after four years of age.

• Plasma Pyrolysis Technology

Plasma Pyrolysis Technology (PPT) integrates the thermochemical properties of plasma with the pyrolysis process. The intense and versatile heat generation capabilities of PPT enable it to dispose of all types of plastic wastes including polymeric, biomedical and hazardous waste in a safe and reliable manner. Waste is not burnt like incinerator but broken into gas and solid waste at very high temperature produced by electric arc in plasma chamber. Plastics waste is fed into the primary chamber at 8500oC through a feeder. The waste material dissociates into carbon monoxide, hydrogen, methane, higher hydrocarbons. Induced draft fan drains the pyrolysis gases as well as plastics waste into secondary chamber, where these gases are combusted at about 10500oC.

• Conversion of plastic waste into liquid fuel

In this technique, a random de-polymerization of plastic waste is done into liquid fuel in the presence of a catalyst (HZMS-5 Zeolite). The entire process is undertaken in closed reactor vessel followed by condensation, if required. Waste plastics while heating up to 2700o C to 3000o C gets converted into liquid-vapour state, which is collected in condensation chamber in the form of liquid fuel. Organic gas is also generated in this process which needs to be vented out due no proper storage facilities available. This gas can also be used in dual fuel diesel-generator set for generation of electricity. If PVC waste is used, chlorine gets converted into hydrochloric acid which is a useful by-product.

• Use of plastic waste in concrete as partial replacement for sand

Plastic waste can be effectively utilised as partial replacement for sand in concrete. Frigione (2008) reported the benefits of utilising un-washed PET bottles pieces as fine aggregate in concrete to the tune of 5% by weight of fine aggregate. Compressive strength tests conducted on the specimens with different cement content and water/cement ratios at 28 days and 365 days, resulted in slight decrease in compressive strength at 365 days with respect to the value measured at 28 days is similar for the WPET and normal concrete. The stress-strain curve from compression test data was plotted and it was observed that the two system display very similar compressive strength curve. Bandodkar et al. (2011) utilised three types of plastic waste viz. pulverized carry bags, pulverized injection moulded plastic and pulverized PET bottles as three alternatives for replacement of sand in concrete to the tune of 1%, 5% and 10%. It was observed that 28 days compressive strength reduced by about 13.5% and 10.5% than the conventional concrete comprising of cement, sand and coarse aggregates, when PET bottle and injection mould plastic was used as partial replacement for sand to the tune of 10% . However, only 3.5% reduction in the 28 days compressive strength was observed in the case of pulverized carry bags waste used in concrete. It was concluded that such concrete with plastic waste cannot be used in structural elements under present conditions however it can be used as plain cement concrete. This project was carried out so as to find out possible solution for management of plastic waste and also to tackle the problem of shortage of supply of natural sand for concreting works.

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LANDFILLS – ENGINEERED AND SUSTAINABLE

Engineered landfills offer better solution for municipal solid waste management. These landfills are designed and operated to minimize environmental impact. Engineered landfills require proper planning, geotechnical and hydro-geological study, proper design of bottom liners, side liners, top covers which comprise of geosynthetics/geomembranes, design and operation of leachate and gas collection system, operation and maintenance, constant monitoring, testing, and reporting throughout the life of the landfill. The wastes in these landfills however take more time to decompose since this biodegradation process is slow process. However, this can be done at faster rate by introducing leachate back into the landfills. Recirculation of leachate back into landfills enhances the biodegradation process. These types of landfills are known as bioreactor landfills. A schematic sketch of bioreactor landfill is shown in Figure 5.

Fig 5: Schematic sketch of a Bioreactor Landfill (Walsh and O’Leary, 2002)

Since decomposition is faster in the case of bioreactor landfill, the volume of waste gets reduces considerably thus creating more space for additional loads of waste. It has been observed that bioreactor landfills results in saving of up to 30% of space. This technology is much helpful where cost of land is more and also where land available is very scarce. In addition bioreactor landfills offer additional advantage of less time required for monitoring as compared to conventional landfills. Sustainable landfill (Hettiarachi, 2006) is a further improvement over bioreactor technology. Sustainable landfills are the ones in which part of landfill is converted into compost by using modified bioreactor technology and can be removed since it has good value as manure value, thus creating place for new landfill cell. This is accomplished in three stages. Anaerobic bioreactor stage involves recirculation of leachate to recover the full energy content of organic waste. During the aerobic stage, the landfill operates in an aerobic mode producing compost-like material. The third stage involves mining of the compost and creating space for new landfill cell. This concept is extremely useful where there is space crunch and cost of land is high. These techniques can be effectively adopted in both the cities of Ponda and Panaji.

CONCLUSIONS This paper discusses important aspects of municipal solid waste management in the cities of Ponda and Panaji. Practices of solid waste collection in these cities are reviewed. Various recycling techniques like recycling, use of plastic waste in roads and concrete, converting plastic waste to

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fuel and plasma pyrolysis techniques were discussed. Alternatives for handling of municipal waste like engineered or bioreactor and sustainable landfills were suggested. References Bandodkar, L., Gaonkar, A., Gaonkar, N., Gauns, Y., Aldonkar, S., Savoikar, P. (2011), Pulverised PET

Bottles as Partial Replacement for Sand. Intl. Journal of Earth Sciences and Engg. 04 (06) SPL: 1009-1012.

Frigione, M. (2010), Recycling of PET bottles as Fine Aggregate in Concrete. Waste Management, 30, 1101-1106.

Hettiaratchi, J. (2006), Bio-Cell Project.www.eng.ucalgary.ca/resrch_civil/bio-ellproject/ Hettiaratchi-bio-cellproject.htm.

Hopewell, J., Dvorak, R. and Kosoir, E.(2009), Plastic Recycling: Challenges and Opportunities. Phil. Trans. R. Soc., B364: 2115-2126.

Walsh P, O’leary, P (2002), Landfill Bioreactor Design and Operation. Waste Age, June, 72-76.

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DAMAGE IDENTIFICATION AND BEHAVIOR OF SLABS USING EXTERNAL LAMINATES:

A REVIEW PAPER

H. K Gaba, H S Rai and S P Singh* Department of Civil Engineering, Guru Nanak Dev Engineering College, Ludhiana

*Department of Civil Engineering, NIT Jalandhar

Abstract: Slabs are one of the most widely used structural elements. The function of slabs is to resist loads normal to their plane. In many structures, in addition to support transverse load, the slab also forms an integral portion of the structural frame to resist lateral load. In spite of their widespread use, there has never been a universally accepted method of designing all slabs systems. In addition to supporting lateral loads. Slabs act as deep horizontal girders to resist wind and earthquake forces that act on a multistoried frame. In recent years a number of studies on the use of external laminates on slabs along with their distinguishing features have been proposed. This paper presents a survey of health monitoring and retrofitting materials on slabs. This survey allows us to identify the areas for future research.

Keywords: Slab, Structural Health Monitoring, Retrofitting, Laminates

INTRODUCTION Slabs are most widely used structural elements of modern structural complexes and the Reinforced concrete slab is the most useful discovery for supporting lateral loads in buildings. Slabs may be viewed as moderately thick plates that transmit load to the supporting walls and beams and sometimes directly to the columns by flexure, shear and torsion. It is because of this complex behavior that is difficult to decide whether the slab is a structural element or structural system in itself. In addition to supporting lateral loads, slabs act as deep horizontal girders to resist wind and earthquake forces that act on a multi-storied frame.

The deterioration of structures is a problem that has become a challenging issue in the construction industry. The reasons for this may include unsatisfactory detailing, incorrect selection or specifications, temperature variations, fire; natural hazards i.e. earthquakes, wind storms, crack formations, unsatisfactory maintenance, etc. A structure when damaged has to be inspected and repaired. This can be costly and time-consuming. Another reason that complicates the situation lies in the fact that the damaged member may be hidden within the structure, below water or below the ground surface. The structure has to be monitored time and again for its proper functioning The restoration of strength by application of adding an extra material on slab has also achieved tremendous importance these days.

LITERATURE REVIEW

Externally bonded FRP laminates and fabrics can be used to increase the strength of reinforced concrete beams, slabs and columns. This paper presents the previous studies done on retrofitting

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and health monitoring of slabs. This review enhances the scope in the areas of damage identification and retrofitting. The brief summary of research is presented in this paper.

Bracci et al (1997) evaluated seismic performance of a three-story reinforced building which was subjected to shaking table excitation. The demand and capacity curves were compared to experimental responses. Pushover analysis was found to be more rational and consistent than under seismic loading. This procedure proved helpful for assessing the new as well as existing structures.

The pushover analysis for RC framed structures was studied by Lakshamanan (2006) and it

was found that the strength decreases with the number and amplitude of cycles and that some deficiencies in the detailing of slab-column joints is reflected even after repair. As it was observed, there was a significant load drop in the post-peak load behavior because of inherent detailing deficiency in the slab-column junction. These incoherent deficiencies in the detailing of slab-column joints get reflected even after repair. There was a need to evolve suitable performance factors when the system shows a negative stiffness.

The study of crack pattern using two-dimensional testing techniques i.e electrical resistivity and ultrasonic surface waves was done by Goueygou et.al (2008). Test specimens of rectangular reinforced concrete slabs with dimensions (60x60x60) cm were made with three different mixes. Electrical resistivity measurements were done using four probes square device. The investigations were done along two 30cm long profiles parallel to reinforcement bars. Ultrasonic transducers were used to generate and receive Rayleigh waves. Two setups were made. Ultrasonic signal was acquired at each 1 cm step for setup A and 0.5cm step for setup B. Four profiles, 15cm long were used for setup B to cover entire length of specimen and single profile was used for setup A. It was observed that the main crack was located at origin of horizontal axis. Resistivity was found to be around 200-300 Ωm. Loading levels 0 and 1 showed similar resistivity variations while levels 2 and 3 reached below 50Ωm and detection of crack was 5cm before and after its location. The decrease in resistivity at the crack location indicated that it is partially filled with water to moisten specimen surface

The Ground-penetrating radar (GPR) technique of Non-destructive testing was used by V. Perez-Gracia, V. et.al (2008) to evaluate damage in Reinforced concrete base of block of flats. GPR survey was carried out to detect areas affected by cracks and defects in water-tightness of base to evaluate and determine extent of damage. The slab was 15cm thick and reinforcement was observed at base. The radar images of the areas were obtained that showed damage on the surface. High reflective sections correspond to wetter areas with low wave velocities.

The thickness of slab perimeter profiles was found at about 3ns two-way travel time. Velocity of 10 cm/s was used to convert time into depth using equations which gave a result of depth of 15cm. Strong filtering effect was indicated due to high water saturation and the center frequency antenna was near 200 MHz. In the high frequency antennas, there was no penetration into lower layers.

Results of analysis made from the use of rubbercrete based on Ultrasonic pulse velocity (UPV) and Rebound hammer (RH) test were reported by Mohammed Bashar. S et.al (2011). Specimens were casted with different water-cement (w/c) ratios of 0.41, 0.57 and 0.68. For each w/c ratio, the crumb rubber percentage varied from 0% to 30%. After drying of cubes, each of the four faces of concrete cubes was prepared for RH test. Thereafter, the cubes were prepared for

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ultra pulse velocity test after spreading a thin layer of couplant on each of the four faces. A linear transformation was conducted to validate the models by statistical analysis by using Excel spreadsheet.

It was observed that there was a decrease in unit weight and increase in air content with an increase in crumb rubber replacement. A comparison was made between all the mixtures and it was seen that there was also a decrease in rebound numbers with an increase in w/c ratio from 0.41 to 0.68 as it lead to an increase in surface hardness. RH test is more dependent on the properties of rubbercrete mixture than UPV test. Therefore, the UPV test is more realistic in evaluating rubbercrete mixtures.

The performances of reactive powder concrete, RPC, as a new repair and retrofitting material was assessed for durability by Lee, Ming-Gin et.al (2006). The materials for cement-repair were Regular Concrete (RC) and High Strength Mortar (HSM) with 10% silica fume. RPC was used as a retrofitting material. Freeze-thaw cycle acceleration deterioration test was used to evaluate bond durability. Blocks were subjected to Freeze-thaw cycles at a rate of one cycle per 185 minutes as per with ASTM C666 (1997). For flexural and compressive strengthening tests, flexural beams and cylinders were cast. For the rebar pull out tests, a total of 24 concrete cylinders were used.

The effects of Flexural strengthening with bonding RPC of 10 mm and 20 mm thickness are about 150% and 200% more than those of normal strength concrete. The effects of compressive strengthening with bonding RPC of 10 mm and 20 mm thickness are about 200% and 300% more than those of normal strength concrete. The values of the relative dynamic modulus of elasticity based on resonant frequencies at 300, 600 and 1000 cycles were 75, 55 and 39 percent, respectively, compared with the corresponding values of 96, 92 and 90 percent for RPC. RPC not only enhances the maximum bond stress but also resists freeze-thaw cycling.

Tests conducted by Hashemi and Mahaidi (2010) have shown that excellent bonding properties can be achieved using the cement based adhesives. Tests include the investigation of bond strength of FRP fabrics and flexural behavior of FRP strengthened reinforced concrete beam using cement based adhesives. The specimens were 245×75×75mm3 concrete prisms. The surface of the specimen was sand blasted to achieve a high level of bonding between mortar and concrete. CFRP material was applied in two different shapes including fabric and textile, with equal crosssection area of CFRP. The tests had been performed on specimens having different bond lengths. This included 100mm and 180mm bond lengths with and without end anchorage. The tests showed that the mortar performed adequately as bonding agent in all samples. The anchored prisms showed higher levels of load carrying capacity compared to the unanchored ones.

One beam was retrofitted with 2 strips of CFRP fabric using normal epoxy adhesive. The failure was characterised by a combination of mid-span and end debond. The load carrying capacity was P=161.7 kN, which is 35% higher than the control beam capacity. Cementious mortar adhesive was used to attach 2 layers of CFRP fabric strips to the soffit. Four point bending was done and as the load was progressively increased, a flexural shear crack developed near the point load.

As the load was further increased, most of the fabric was debonded on one side of the beam and the beam started to exhibit a response similar to that of the control beam. The load carrying capacity was P=132.1 kN, which is 10% higher than the control beam capacity. The ultimate load

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which was achieved by using CFRP textile-cement mortar is around 80% of what was achieved by using CFRP fabric with epoxy adhesive.

An emergency retrofit technique utilizing pre-tensioned high steel bars (PC bars) and steel plates was experimentally investigated and analytically evaluated by Miyagi et.al (2004). The specimens used in this experiment were shear sensitive columns with square cross sectional dimension of 250x250mm. The axial compression tests were carried out at three times: first, for confirmation of residual axial compression capacity immediately after damage and before emergency retrofitting; second, for confirmation of restorable axial strength immediately after emergency retrofitting; and third, for confirmation of residual axial compression capacity after final cyclic loading test. Cyclic loading tests were carried out twice, before and after emergency retrofitting. An emergency retrofit on damaged columns by utilizing pre-tensioned high strength steel bars (PC bars) and steel plates, is confirmed to prevent shear failure, to recover lateral capacity and to improve ductility. This means that if columns can still maintain axial force after an earthquake, it is possible that the lateral capacity can be recovered and also the ductility can be improved.

The focus of the research carried out by Aboul-Anen, Boshra et.al (2009) on the composite action of the ferrocement slabs and steel sheets. The experimental models of ferrocement slab with and without steel sheeting and their numerical models using the finite element method were presented. Finite element models are developed to simulate the behavior of the slab through nonlinear response and up to failure, using the ANSYS package.Both slabs FS1 and FS2 were tested utill failure. The failure load was measured for both slabs as 7.18 kN, and 31.42 kN; respectively. The crack pattern in FS1 is shown in Figure 1. In FS2, as load was applied a crack occurred between the steel sheet and the slab. This is contact failure happened around load of 10 kN as shown in figure 2. The ultimate load predicted by the theoretical model was higher than the experimental one with only 7.89%. The ANSYS model accommodates material non-linearities, cracking and crushing of concrete (or mortar) and yielding of the steel sheeting and wiring meshes. The analytical results compared well with the experimental for the ferrocement slabs without steel sheeting.

Fig.1 Crack Pattern of Slab FS1

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Fig.2 Crack Pattern of Slab FS2

CONCLUSIONS The deterioration of a reinforced cementitious materials or elements is a complex problem. The catastrophic accidents clearly show the destructive power of any damage that may start from a minor level. Hence, even a minor damage should not be ignored since it carries the potential to cause damage and cause failure either leading to a wide scale of loss of life and property, or halting some revenue earning activity or both. It is this possibility which calls for inspection of structures on a regular basis or in other words Structure Health Monitoring and restoration of strength of the structure or retrofitting.

The Structural Health Monitoring and retrofitting of structures is a growing step in the field of construction industry. In this paper, an up-to-date survey of most major has been done. The challenges and basic concepts of Structural Health Monitoring and retrofitting of structures have been reviewed. Most of the important advances in the field are covered. Many areas of research in this field provide considerable challenge and potential to enhance the growth and proliferation and applications. For each research contribution, the functionality and main features are described briefly so as to explore the future areas of research.

ACKNOWLEDGEMENTS

The data reported in this study is based on information provided from several research papers. The authors would like to thank all those who have helped directly or indirectly in compiling the information and All India Council for Technical Education for funding the ongoing PhD work of first author in the form of grant under RPS awarded to department of civil engineering of the college.

References

Bracci, J.M., Kunnath, S.K. and Reinhorn, A.M. (1997). Seismic performance and retrofit evaluation of reinforced concrete structures, Journal of Structural Engineering, ASCE, 123 (1) 3-10

Lakshamanan, N (2006). Seismic Evaluation and Retrofitting of buildings and structures, ISET Journal of Earthquake Technology, Issue No.469, 43 (1-2) 31-48.

Lee, Ming-Gin., Kan Yu-Cheng and Chen, Kuei-Ching (2006). A Preliminary Study of RPC for Repair and Retrofitting Materials, Journal of the Chinese Institute of Engineers, 29 (6) 1099-1103.

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Goueygou, M. et.al, (2008) “A comparative Study of two non-destructive testing Methods to assess near-surface mechanical damage in concrete Structures”, NDT& E International, 2008, 41, 448-456.

Boshra Aboul-Anen, Ahmed El-Shafey, and Mostafa El-Shami (2009) Experimental and Analytical Model of Ferrocement Slabs, International Journal of Recent Trends in Engineering, Vol. 1, No. 6, pp 25-29.

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SEISMIC MICROZONATION – A STUDY

Rajiv Chauhan and Surender Singh Department of Civil Engineering, Deen Bandhu Chhotu Ram University Of Science And Technology,

Murthal , Sonepat, Haryana, India

Abstract: A large proportion of world’s population is living under the threats of earthquakes. In the past century earthquakes have killed an average of 20,000 people a year throughout the world, with 80% of fatalities occurring in developing countries. Moreover, the urban cities in developing countries are increasingly more vulnerable than those in developing countries. India is a vast country with respect to its geological and geophysical characteristics of soil and earthquake parameters such as ground shaking magnitude, amplification etc. Liquefaction susceptibility of such areas makes problem more devastating. Therefore, seismic hazards at different locations within the area should correctly be identified. Microzonation provides the basis for site-specific risk analysis, which can assist in the mitigation of earthquake damages. In most general terms, seismic microzonation is the process of estimating the response of soil layers under earthquake excitations and thus the variation of earthquake characteristics on the ground surface. The present study explores the various methods and techniques developed for seismic microzonation and to find their suitability with respect to regions.

Keywords: Liquefaction, Earthquake, Geophysical, Urban cities, Ground shaking

INTRODUCTION

Seismic microzonation is defined as the process of subdividing a potential seismic or earthquake prone area into zones with respect to some geological and geophysical characteristics of the sites such as ground shaking, liquefaction susceptibility, landslide and rock fall hazard, earthquake-related flooding, so that seismic hazards at different locations within the area can correctly be identified. According to Arya (2004), India has experienced, the most disastrous earthquakes (Fig. 1 and Fig 2) like Assam (Year 1897, M = 8.7), Kangra (Year 1905, M = 8.6), Bihar-Nepal (Year 1934, M =8.1), Assam-Tibet (Year 1950, M = 8.7), Burma –India( year 1988, M=8.1), Latur (Year 1993, M = 6.4), Chamoli (Year 1999, M = 6.8) and Bhuj (Year 2001, M = 7.6) in the past,. Microzonation provides the basis for site-specific risk analysis, which can assist in the mitigation of earthquake damages. In most general terms, seismic microzonation is the process of estimating the response of soil layers under earthquake excitations and thus the variation of earthquake characteristics on the ground surface.

Regional geology can have a large effect on the characteristics of ground motion. The site response of the ground motion may vary in different locations of the city according to the local geology. A seismic zonation map for a whole country may, therefore, be inadequate for detailed seismic hazard assessment of the cities. This necessitates the development of microzonation maps for big cities for detailed seismic hazard analysis. Microzonation maps can serve as a basis for evaluating site-specific risk analysis, which is essential for critical structures like nuclear power plants, subways, bridges, elevated highways, sky trains and dam sites. Seismic microzonation can be considered as the preliminary phase of earthquake risk mitigation studies. It requires multi-disciplinary contributions as well as comprehensive understanding of the effects of earthquake

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generated ground motions on manmade structures. Many large cities around the world have put effort into developing microzonation maps for the better understanding of earthquake hazard within the cities. India has experienced most disastrous earthquakes in the recent past (Fig. 2). The earthquakes can neither be predicted nor be prevented.

Fig.1 Burma –India Earthquake (1988)

Fig. 2: Bhuj (2001) Fig.3: Turkey (2004)

The liquefaction of saturated sand generated by earthquake loading does tremendous damage to Civil engineering structures (Fig. 2 & 3). One of the major reasons for collapse of structures during earthquakes is loss of strength due to generation of excess pore. pressure and subsequent liquefaction of saturated sandy soils. The present paper explores review, significance and methods for seismic microzonation.

FACTORS AFFECTING SEISMIC MICROZONATION • Earthquake

The sudden movement within the crust or mantle, and concentric shock waves move out from that point. Geologists and Geographers call the origin of the earthquake the focus. Since this is often deep below the surface and difficult to map, the location of the earthquake is often referred to as the point on the Earth surface directly above the focus. This point is called the epicentre. The strength, or magnitude, of the shockwaves determines the extent of the damage caused. Soil Amplification

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Seismologists have observed that soils repeatedly experience stronger seismic shaking than others. This is because the ground under these regions may be relatively soft. Soft soils amplify ground shaking. If, in contrast, soft soil always amplifies shear waves. If an earthquake is strong enough and close enough to cause damage, the damage will usually be more severe on soft soils.

• Shear Wave Velocity

One contributor to the site amplification is the velocity at which the rock or soil transmits shear waves (S-waves). Shaking is stronger where the shear wave velocity is lower. The National Earthquake Hazards Reduction Program (NEHRP) has defined 5 soil types based on their shear-wave velocity (Vs). These modified definitions are, based on studies of earthquake damage in the Bay Area. The modified definitions are given in Table 1.

• Soil Liquefaction

Liquefaction is a phenomenon in which the strength and stiffness of a soil is reduced by earthquake shaking or other rapid loading. Liquefaction and related phenomena have been responsible for tremendous amounts of damage to structures. Liquefaction occurs in saturated soils, that is, soils in which the space between individual particles is completely filled with water.

Table 1: Soil Type and Shear wave Velocity

Soil Type

Shear Wave Velocity

Content of Soil/rock

Soil type A

Vs> 1500 m/sec

Includes unweathered intrusive igneous rock. Occurs infrequently in the bay area. We consider it with type B (both A and B are represented by the color blue on the map). Soil types A and B do not contribute greatly to shaking amplification.

Soil type B

1500 m/sec >Vs> 750 m/sec

Includes volcanics, most Mesozoic bedrock, and some Franciscan bedrock. (Mesozoic rocks are between 245 and 64 million years old. The Franciscan Complex is a Mesozoic unit that is common in the Bay Area.

Soil Type C

750 m/sec >Vs> 350 m/sec

Includes some Quaternary (less than 1.8 million years old) sands, sandstones and mudstones, some Upper Tertiary (1.8 to 24 million years old) sandstones, mudstones and limestone, some Lower Tertiary (24 to 64 million years old) mudstones and sandstones, and Franciscan melange and serpentinite.

Soil Type D

350 m/sec >Vs> 200 m/sec

Includes some Quaternary muds, sands, gravels, silts and mud. Significant amplification of shaking by these soils is generally expected.

Soil Type E

200 m/sec >Vs Includes water-saturated mud and artificial fill. The strongest amplification of

shaking due is expected for this soil type.

MICROTREMOR METHODS OF SESIMIC MICROZONATION

Nakamura (1996) developed an experimental method, which is very widely used in site response studies. This method is based on the basic assumption that the effect of surface waves can be either eliminated or neglected such that the end result is in direct relationship with the transfer function for S-waves. Nakamura (1996) separated the ambient noise into body waves and surface waves as:

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SNH(f) = SbH(f) + SsH(f)= HT(f). RbH(f) + SsH(f)

SNV(f) = SbV(f) + SsV(f) = HV(f). RbV(f) + SsV (f)

where, RbH is the horizontal spectrum of the body wave part of the noise at the reference site. H/V

ratiobetween SNH(f) and SNV(f) can be written as:

ANHV= [HT .ArNHV+ β AS] / [VT + β]

Where, ArNHV is the H/V ratio at rock site, β is the relative proportion of surface waves in the noise

= SsV(f) /Rb

V(f) and AS is the horizontal to vertical ratio due to surface wave only i.e.,

SsH(f) / SsV(f)

This method is based on the assumptions that the vertical component is not amplified at the fundamental frequency (fHO), H/V ratio on rock is equal to 1 at fHO , β is much smaller than one at fHO and β AS (fHO) is also much smaller than HT(fHO). Kobayashi et al. (1996) measured microtremors in both arbitrary site and reference strong motion site in Mexico city. They concluded that the product of H/V ratio and the spectrum of the strong motion at the reference site can predict the strong motion at arbitrary site. Nakamura (1996) carried out extensive microtremor studies and demonstrated capability of the method for site response studies. He conducted the microtremor tests in Kanonomiya and Tabata, Japan and concluded that the H/V ratio provided reliable estimation of site response of S wave. The method also reliably estimates not only the resonant frequency but also the corresponding amplification of a site.

Comparison with other experimental techniques by different investigators shows that the Nakamura method allows obtaining, very simply, the fundamental resonance frequency. Also, the method has proved to be one of the most inexpensive and convenient techniques to reliably estimate fundamental frequencies of soft deposits.

CASE STUDY

This microtremor tests were carried out in Delhi at 144 locations for estimating the local site effects. Microtremor method is useful for determining local site effects in seismically active regions such as Delhi, where ground motion records are few, and the noise levels are high due to urbanization. This study was done in Delhi NCR at 144 different stations and the measurements were taken using velocity sensors for a period of 1 hr at each station point. The locations of the test sites are shown in Figure 5. A differential GPS system provides the geographic position of each measurement point.

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Fig 5: Locations of the Microtremor Tests Carried out in Delhi

• Data Acquisition

The microtremor tests were carried out using MR2002-CE vibration monitoring system from SYSCOM, Switzerland, which ensures accurate, reliable vibration measurement and long term monitoring. The MR2002-CE is easy to handle and ready to use. The instrument has two main units i.e., one is vibration sensor (MS2003+) with three sensitive geophones which picks up the ground vibrations, other one is the recorder (MR2002) in which all the data will get stored. The MR2003+ velocity sensor is highly sensitive with three orthogonal components that is two horizontal (H) and one vertical (V). Figure 6 shows the field set up of the microtremor equipment. First the sensor is placed on the ground and the mounting plate of the sensor is leveled using the screws. Then both are connected using a sensor cable and recorder is connected to the field laptop using communication cable.

Recorder is switched on and WINCOM 2002 is started from the laptop to get access to the MR2002. A baseline correction will be performed which assures that the recorded signal is centered around zero even if the sensor is not 100% level. This correction has to be done before starting the recording at every site. The recorder records the ground vibrations continuously and creates different files of one minute each. The data is recorded continuously for one hour at each site creating 60 data files of one minute each of ambient vibration data. The data recorded using this compact triaxial vibration monitoring equipment is analyzed using VIEW2002 software.

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Fig 6: Field Setup during the Microtremor Testing

• Analysis of the Data

VIEW2002 is the data analysis software specifically developed for the MR2002-CE vibration recorder. It is a comprehensive, sophisticated and high performance signal processing program. In this study the horizontal versus vertical (H/V) spectra using Nakamura method is estimated using VIEW 2002 software. The signal of pure ambient ground noise that is free from spurious noise, man-made and cultural noise signals are selected. All the 60 one minute files of a particular test site, which are recorded in a compressed format, are selected collectively and processed from the file group option. The final plot of the program includes the H/V ratio and the H/V amplitude. For clear identification of peak frequency, spectra need to be smoothened. In the present study also smoothing was performed using moving average technique. The analysis was performed for all the 144 sites and a classification is also proposed.

RESULTS AND DISCUSSION

The H/V response curves obtained from the microtremor survey is exactly reflecting the geology and soil properties of the test location. That is Nakamura H/V curve at the locations with rock outcrops, gravelly deposits are having more or less flat curves with a very slight amplification and at the locations with high soil cover with loose soil deposits have a peak curve with high amplification at low frequencies .Depending on the shape of the response curve and the estimated resonance frequency all the sites are classified into four categories (T1, T2, T3 and T4). It is observed that in the locations falling in the Southern Delhi (T1category) has very high resonance frequency (> 4.0 Hz) because of rock outcrop and presence of gravelly deposits. The shape of the T1 type response curves is almost flat where as the shapes of the T2, T3 and T4curves has a very significant peak at 2.0 to 4.0 Hz, 1.0-2.0 Hz and < 1.0 Hz respectively. The peak of the response spectra get shifted towards lower frequencies (left side) from T2 type to T4 type. That means it is high in the dense or gravelly strata and decreases with the soft sedimentary deposits. In the Eastern side of Delhi i.e., especially trans Yamuna region (Newer alluvium) with alternative layers of silty sand and sandy silt (low SPT values and high water table) have resonance frequency less than 1.0 Hz. The places located in the western and northwestern part of Delhi has resonance frequency greater than the frequencies in T4 type because of the presence of dense silty sands and sandy silty with clay seams (Older Alluvium). This classification can be used to estimate the range of fundamental resonance frequency at any location with the known geotechnical and geological data.

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That is, in the locations like JNU Campus, Vasanth Kunj, Ladha Sarai, Suraj Kund, Lotus Temple, Citharanjan Park, Malai Mandir, etc which are on the rock out crop in the southern side of Delhi, has predominant frequencygreater than 4.0 Hz. In western and southwestern side of Delhi areas like JanakPuri, Hari Nagar, Dashrathpuri, Shekhawati Lines, Near Prahaldpur Village, Dwarka which are having dense sandy silts and silty sands with high SPT ‘N’ values have the resonance frequency between 2.0 to 4.0 Hz.. The sites which are falling in northern side of Delhi like Shalimar Bagh, Kanhaya Nagar, MalkaGanj, with alternate layers of sandy silt, silty sand with seams of clayey silt have the resonance frequency from 1.0 to 2.0 Hz and the locations like Shahdra, Rohini, Nithari,Yamuna Vihar, Pansali, Khadirpur, Noida, SaritaVihar, Ali Vihar having loose deposits of sandy silt and silty sands in the eastern part (trans Yamuna) have resonance frequency < 1.0 Hz. From the above it is clear that the predominant frequency map fairly correlates with geological and geotechnical aspects in the region.

CONCLUSION

The earthquakes can neither be predicted nor be prevented. However, the severity of the damages can be minimized by proper land use planning and safe construction practices. Seismic microzonation provides the required information for the effective mitigation of seismic hazards. Local site effects play major role on the severity of damages observed during earthquake shaking. Local soils modify the bed rock motions significantly depending upon their geotechnical characteristics, local topography, and hydrogeological site conditions. Earthquake associated disasters such as occurrence of liquefaction, landslides etc., are also depend upon the geotechnical characteristics of the local soils and their disastrous effects can be minimized with use of seismic microzonation studies for developed cities and important civil engineering structures .

References

Arya, A.S. (2004), “Engineering role in disaster Reduction in India”, Proc. World Congress on National Disaster Mitigation, Kolkata, India.

National Disaster Management Authority (2011), “ Development of Probabilistic Seismic Hazard Map of India. Govt. of India

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CHAR WASTE REUSE AS ROAD MATERIAL

K. G. Guptha* and S. A. Kakodkar** *Professor and Head, Civil Engineering Department, Goa College of Engineering, Farmagudi –Goa

**Astt. Professor, Civil Engineering Department, Goa College of Engineering, Farmagudi –Goa

INTRODUCTION

Hot-Mix Asphalt (HMA) mixtures are complex materials composed of mineral aggregates and asphalt binder. About 95 percent by weight of the HMA mixture is aggregate. The coarse and fine aggregate properties influence pavement performance significantly. Studies have shown that, HMA pavement rutting and stripping can be directly related to improper selection and use of aggregates. Tests and associated criteria used by highway agencies to select aggregate for HMA mixtures are empirical. Often, they have not been related to pavement performance directly. Aggregate tests that provide clearer relationships with performance will provide better means for evaluating and selecting aggregates.

Present study deals with understanding the material produced in Goa Sponge and Power Ltd (GSPL) about its suitability related to Asphalt Concrete Performance in Pavements. A set of performance-related aggregate tests for evaluating aggregates for use in HMA pavements were carried out. Pavement performance indicators assumed to be related to these laboratory aggregate tests where permanent deformation because of traffic loading (both with and without stripping), fatigue cracking, and surface defects (e.g., raveling, popouts, and potholes).

The study on “Char Waste Reuse as Road Material" recommends the use of Char aggregates in wearing coat, bitumen macadam, and wet mix macadam in road construction. Various physical parameters, chemical tests, combination of Char aggregates with conventional aggregates, binding parameters of it with the bitumen were evaluated through laboratory tests as per relevant IS Code and MoRTH (Ministry of Road Transport and Highway) specifications.

The objective of conducting physical and chemical tests were to get a better idea about the material properties, suitability of the material, and if it satisfies or qualifies the code requirements. Bitumen moulds were casted for Char aggregate and for combinations with conventional aggregate for various layers with different bitumen content. This was carried out to verify the load it can take and to find its flow value using Marshall Stability test. The material selected for detailed studies are processed solid waste produced in Goa Sponge and Power Limited (GSPL). This material is termed as Char waste.

TESTS AND METHODOLOGY

Strength of any road depends mainly on its aggregates and their interlocking. Aggregates are arranged in their ascending order of CBR from seal coat to sub base. Selection of aggregates and fitting them to specifications stipulated by controlling authorities is totally depends on engineering properties of constituting material.

• Study Area

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Case study involved the reuse of Char aggregate in the new hot mix road from NSN/CCPL to GSPL junction and repair of road up to Guddemol junction. The existing road had a width of 7.05m and run for a stretch of 3.2km starting from Saibaba junction to Fomento mines. Approach roads of GSPL and Chowgule mines for a stretch of 600m each required repair works too. Since these roads are located in heavy transport affected areas, they are subjected to constant heavy loadings of trucks, each carrying a load of 15-20 tones. Due to improper drainage and being located in an area subjected to heavy rainfall the roads are exposed to adverse environmental conditions which influence fast rate of deterioration.

The work involved not only repairing but also widening and maintaining proper camber for the road. The construction of new work involved excavation and leveling, laying of WBM, BM layers (BM-I and BM-II) and AC coat. The repair work involved the proper treatment for existing road and then laying BM and AC. Test on aggregates were found and Tabulated in Table - 1.The grading on recommendation adopted by the hot mix plant is shown in Table - 2.

Fig. 1 Location Plan

Table 1: Physical Tests

Sr. No

Test Method Char Waste Conventional Aggregates

1 Specific Gravity IS 2386 (Part III)

3.02-3.48 2.53-2.98 2 DLBD 1632.33 1341.33-1728.66 3 Bulk Density 1803-1833.33 1524.4-1671.3 4 Impact Value

IS 2386 (Part IV)

6.57% 15.66 - 17.80% 5 Crushing Value 7.66% 12.16% 6 Abrasion Value 14.10% - 7 Water Absorption IS 2386 (Part

III) 9.00 % 1.01 %

8 Moisture Content 0.25% 0.5 %

9 Fineness Modulus 8.12 5.36

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Table2: Grading suggested to Hot Mix Plant

Layer 40mm 20mm 10mm 6mm Fines Bitumen

WMM - 26% 33% 17% 16% - BM-II - 30% 50% 20% - 4.5% BM-I - 30% 50% 20% - 5.5% AC - - 30% 70% - 6.5%

• Sequence of operations carried out

Work began with the preparation of site from Fomento end. This involved cleaning of site, excavation, widening and leveling followed by rolling of sub grade. The proposed work included construction of new road with WMM and hot mix from Fomento to GSPL junction and hotmix with pothole repairs from GSPL junction to Guddemol junction.

• Wet mix macadam layer

On completion of preparation of sub grade the work of laying of WMM was commenced. A job mix was prepared and the design comprised of 40mm-25%, 20mm-20%, 12.5mm-20%, 5.6mm-25%, fines-10% proportion. Char aggregates were used as a replacement for 5.6mm and downsize conventional aggregates and it constituted 25% of the total design mix. Following aspects were taken into consideration while laying WMM: i) Stack yard: Aggregates of various sizes to be used in WMM were laid in the form of layers at the stack yard. ii) Water usage: Water was poured on the mix in dry state. Water tankers of 6000 litres capacity were used. Care was taken to spray the water as per requirement of the mix. iii) Transport: Tippers of 25 tonnes capacity were used to transport the WMM from stack yard to the site. iv) Initial laying and compacting: The sub grade was required to be prepared before laying of WMM. First the sub grade was wetted with water and any unevenness was corrected by cutting and filling. Finally it was rolled using Vibro Compactor. v) Laying of WMM: The WMM transported by the tippers was dumped on the prepared sub grade. With the help of crawler dozer the mix was spread to the uniform thickness. Then using vibro compactor it was compacted to the final thickness as specified.

• BM-II Layer

BM-II layer was laid above the WMM layer from Fomento mine to GSPL junction. The grading suggested to the mixing plant was 20mm-30%, 10mm-50%, 6mm-20% and the percentage of bitumen adopted was 4.5%. The mixing temperature adopted was 1600C and was laid at 1500C. The hot mix was then transported to the site and then laid by "Apollo Sensor Paver AP-550". It was then compacted by "Ingersoll-Rand" vibratory compactor of 11 tonne capacity.

• BM-I Layer

BM-I layer was laid above BM-II, it was laid above WMM directly in the places where the road needed minor repairs. The grading proposed to the mixing plant after recommendation was 20mm-30%, 10mm- 50%, 6mm-20% and the percentage of bitumen adopted was 5.5%. The

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laying and mixing temperature were the same as that of BM-II. The laying and compaction was same as that for BM-II layer.

• AC Layer

AC layer was laid above BM-I. The grading suggested to the mixing plant was 10mm-30% and 6mm-70% and the percentage of bitumen adopted was 6.5%. The laying and mixing temperature were the same as that of BM-I. Fines were spread after compacting so as to absorb excess bitumen oozing up after compaction.

RESULTS Based on the experiments conducted at laboratory, field observations and tests after laying road at Ambeudak-Santona were analysed. These results are presented as in the subsequent articles. These values were further compared with codal provisions wherever applicable.

• Preparation of sub-base course

MoRTH specifies grading requirements along with binder contents for the preparation of sub-base course. In the present study WMM has been prepared. Grading was carried out at site with materials so as to satisfy Table - 3 for properties and grading represented in Table - 4. Table - 5 presents final gradation for WMM.

Table 3: Physical requirements of coarse aggregates for wet mix macadam for

Sub -base/base courses

Sr. No

Test Test Method Requirements

1 *Los Angles Abrasion value Or * Aggregate Impact value

IS: 2386 (Part-4)

IS: 2386 (Part -4) or IS: 5640

40 per cent (Max) 30 per cent (Max)

2 Combined Flakiness and Elongation Indices (Total)

IS: 2386 (Pan-4) 30 per cent (Max)

* Aggregate may satisfy requirements of either of the two tests.

Table 4: Grading requirements of aggregates for wet mix macadam

IS Sieve Designation Per cent by weight passing the IS sieve 53.00 mm 100 45.00 mm 95-100 26.50 mm — 22.40 mm 60-80 11.20 mm 40-60 4.75 mm 25-40 2.36 mm 15-30 600.00 micron 8-22 75.00 micron 0-8

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Table 5: Gradation of WMM adopted

Layer 40 mm 20 mm 12.5 mm 6 mm Fines Bitumen

WMM 25 % 20 % 20% 25% 10% -

It is seen from the above table that, better binding and locking of aggregates with coarse and fines were observed when compacted with pneumatic vibro compactor. Actual combination used is presented in Table - 6.

Table 6: Actual observed grading of WMM as per MORTH

Layer 40 mm 20 mm 12.5 mm 6 mm Fines Bitumen

WMM 27 % 21 % 18% 17% 17% - Variation 2% 1% 2% 1%

This adjustment was due to variation in aggregate sizes. Char waste posed no problem while mixing, transporting, placing and compacting. 50% of the 6mm downsize aggregates used in WMM were replaced with Char waste. It was estimated about 225 tonnes was used in the test stretch.

• Preparation of base course

In the present study bituminous macadam (BM) had been prepared and was laid in two layers namely BM-II and BM-I. BM-II was laid over WMM and BM-I was laid over BM-II. Grading was carried at site as per grading – I and grading – II so as specified in Table - 7 for grading and Table - 8 for properties. Table - 9 represents final gradation of BM adopted at the site.

Table 7: Composition of bituminous macadam

Mix designation

Nominal aggregate size Layer thickness IS Sieve (mm)

Grading 1 40 mm

80-100 mm

Grading 2 19 mm

50-75 mm Cumulative %. by weight of total aggregate passing

45 100 37.5 90-100 26.5 75-100 100 19 - 90-100

13.2 35-61 56-88

4.75 13-22 16-36 2.36 4-19 4-19 0.3 2-10 2-10

0.075 0-8 0-8 Bitumen content, % by weight of total mixture

3.1 -3.4 3.3-3.5

Bitumen grade 35 to 90 35 to 90

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Table 8: Physical requirements for coarse aggregates for bituminous macadam

Property Test Specification Cleanliness Grain size analysis1 Max 5 % passing

0.075 mm sieve Particle shape Flakiness and Elongation Index(Combined)2 Max 30 %

Strength Los Angeles Abrasion Value3 Aggregate Impact Value3

Max 40 % Max 30 %

Durability Soundness4

Sodium Sulphate Magnesium Sulphate

Max 12 % Max 18%

Water Absorption Water absorption5 Max 2% Stripping Coating and Stripping of Bitumen Aggregate Mixtures6 Minimum retained

coating 95% Water Sensitivity Retained Tensile Strength Min 80 %

Notes: 1. IS: 2386 Part I 4 IS: 2386 Part V

2. IS: 2386 Part I (the elongation test to be done only on non-flaky aggregates in the sample)

5. IS: 2386 Part III

3.IS: 2386 Part IV* 6. IS: 6241 7. The water sensitivity test is only to be carried out if the minimum retained coating in the stripping test is less than 95% * Aggregate may satisfy- requirements of either of these two tests

Table 9: Gradation of BM adopted

Layer 40 mm 20 mm 12.5 mm 6 mm Fines Bitumen

BM -II - 30 % 50% 20% - 4% BM-I - 30% 50% 20% - 5.5%

It was seen from the above gradation that the mix obtained was good and was well compacted

with pneumatic vibro compactor. Char waste was not used in these layers since 90% of Char particles passed through 6mm sieve.

• Preparation of surface course

Referring to IRC: 29-1988 (for asphaltic concrete), it specifies the requirements of the bituminous concrete mix to be used in AC layer. Table - 1 and 2 of IRC: 29-1988 specifies the requirements of bituminous mix and physical properties respectively. The grading was carried out at site so as to satisfy “Grading 3” requirements which are mentioned in Table – 10 mentioned below (IRC: 29-1968) Table – 11 mention the grading requirements.

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Table 10: Grading requirements for AC layer (source IRC: 29-1968)

Table 11: Gradation of AC adopted

Layer 40 mm 20 mm 10 mm 6 mm Fines Bitumen

AC - - 30% 100% - 6.5%

It was seen from the above grading and bitumen content that the aggregates bound well when compacted with pneumatic vibro compactor.

• Marshall stability test results

The following tables present Marshall Stability test values. Table - 12 presents the Marshall stability test values using conventional aggregates with 4% bitumen.

Table 12: Marshall Stability values (bitumen = 4%)

Mould No.

Height(cm) Weight(Kg) Load(kg) Correction factor

Corrected load value

Flow rate

1 7.8 1.427 1014 0.86 872 287.50 2 7.3 1.389 850 0.86 731 287.50 3 7.5 1.321 1145 0.86 984.7 200.00 Average 1004 862.56 258.33

Table - 13 presents the Marshall Stability test values using 50% conventional aggregates and 50% char aggregates with 4% bitumen.

Table - 14 presents the Marshall Stability test values using conventional aggregates with 4.5% bitumen.

Table - 15 presents the Marshall stability test values using conventional aggregates with 5% bitumen and Table - 16 presents the Marshall stability test values using 100% Char aggregates with 6.5% bitumen

Sieve

Designation

Percent by weight passing the sieve

Grading 1 For 25mm thick course

Grading 2 For 40mm & 50 mm thick course

Grading 3 For 50 mm thick course

26.5 mm -- -- 100 22.4 mm -- 100 82-98 13.2 mm 100 80-100 60-83 11.2 mm 90-100 75-95 55-77 5.6 mm 60-80 55-75 45-65

2.36 mm 40-55 40-55 40-55 600µm 20-30 20-30 20-30 300µm 15-25 15-25 15-25 150µm 10-20 10-20 10-20 75µm 6-9 6-9 6-9

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Table 13: Marshall Stability values (bitumen = 4%) Mould No. Height(cm) Weight(Kg) Load(kg) Correction

factor Corrected load value

Flow rate

1 7.9 1.302 915 0.86 786.9 325 2 7.3 1.178 707.7 0.86 608.62 325 Average 811.35 697.76 325

Table 14: Marshall Stability values (bitumen = 4.5%)

Mould No. Height(cm) Weight(Kg) Load(kg) Correction

factor Corrected load value

Flow rate

1 6.8 1.196 1145 0.86 984.7 100 2 7.2 1.260 850 0.86 731 200 3 7.7 1.270 621 0.86 534.06 100 Average 872 749.92 133.33

Table 15: Marshall Stability values (bitumen = 5%)

Mould No. Height(cm) Weight(Kg) Load(kg) Correction

factor Corrected load value

Flow rate

1 7.2 1.271 1831 0.86 1574.66 100 2 7.1 1.314 1765 0.86 1517.9 100 Average 1789 1546.8 100

.Table 16: Marshall Stability values (bitumen = 6.5%)

Mould No. Height(cm) Weight(Kg) Load(kg) Correction factor

Corrected load value

Flow rate

1 7.0 0.986 327 0.84 275.96 225 2 7.0 1.12 543 0.84 458.24 225 Average 435 367.1 225

• Observed properties of Char

Various physical and chemical tests were carried out on Char aggregates as per relevant IS codes and their results were compared with MORTH specifications and IRC recommendations.

• Sieve analysis

Table – 17 presents the sieve analysis of Char aggregates

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Table 17: Sieve analysis of Char aggregates

Sieve size (mm)

Wt. Retained (gm)

Cumulative weight retained(gm)

Cumulative weight retained%

% passing

20 0.17 0.17 0.02 99.98 16 26.17 26.33 2.63 97.37

12.5 75.04 101.38 10.14 89.86 10 192.42 293.79 29.38 70.62 6 485.79 779.58 77.96 22.04

4.75 153.79 933.38 93.34 6.66 2.36 62.17 995.54 99.55 0.45 1.18 1.17 996.71 99.67 0.33

600 µ 0.17 996.88 99.69 0.31 300 µ 0.17 997.04 99.70 0.30 75 µ 0.17 997.21 99.72 0.28 Pan 0.42 997.63 99.76 0.24

Comparing the sieve analysis to IS: 383 Char waste material may be classified as 10mm downsize material. The fineness modulus was observed to be 8.12.

• Physical properties

Table – 18 presents the comparison of the physical properties of Char material with the normally available conventional aggregates.

Table 18: Physical properties of the Char aggregates

Sr. No.

Experiment Char aggregates Conventional aggregates

1 Specific gravity 3.02-3.48 2.53-2.98 2 DLBD(gm/l) 1632.33 1341.33-1728.66 3 Bulk density(gm/l) 1803-1833.33 1524.4-1671.3 4 Impact value 6.57% 15.66 - 17.80% 5 Crushing Value 7.66% 12.16% 6 Abrasion test 14.10% - 7 Water absorption 9.00 % 1.01 % 8 Moisture content 0.25% 0.5 % 9 Fineness Modulus 8.12 5.36

CONCLUSIONS

• General Conclusions

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i) Properties of Char waste are at par with natural aggregates corresponding to their size or still better.

ii) Char waste are free from silt, deleterious material and free from chlorides and sulphates. iii) These waste have uniform size passing through 12mm and retained on 600 micron

constituting 93% retained above 4.75mm. iv) These are strong, tough, and durable and conforming to specification laid down in

MoRTH. v) Char waste are blackish brown in color and closely conforms to basaltic aggregates.

vi) There were no specific hindrances when blended with natural aggregate in WMM. vii) Char waste can be used directly for AC and result will be better by screening to conform

specification laid for AC by MoRTH. viii) It is an alternative road material proposed, suit and perform better.

ix) Based on the result Char waste is recommended as a road material for WMM and AC.

• Specific Conclusions

ii) Char waste when stack for longer period and exposed to atmosphere turn brownies in color.

iii) Around 50-60% of Char waste is in range of 6-4.75mm.this ensure locking of aggregates in WMM leading to better value of CBR. Thus avoiding usage of any filler material like lime and cement.

iv) Char waste by 50% of total volume of fine aggregate used in WMM did not pose any construction / locking problem during execution.

iv) On vibro-compaction also there was no segregation of Char waste when blended with natural aggregate.

v) Char waste did not pose any problem when blended with bitumen in binding. However initial popping sound when temperature in hot mixed plant rises to 600c when blended with natural aggregate.

vi) No popping sound was observed when use 100% as replacement to conventional aggregates in AC in the mixing plant.

vii) Better result (Marshall Stability, flow value, compaction) were observed between 110-1200C as compared in case of conventional aggregate maintained at 1600C.

viii) At higher compaction and temperature while laying Char waste have shown development of cracks in the pavement and however there are discrepancies as time elapses.

ix) AC when laid with low temperature (110-1200C) and compaction did show neither cracks nor segregation. These facts were also witnessed in analysis of moulds used for Marshall Stability after extraction as courses.

x) No cracks were observed even when subjected to 1/3rd of total monsoon (4 months).

• Recommendations

i) Since naturally occurring aggregates are scarce compared to the present and future demand, Char waste can be used as better substitute.

ii) It’s an eco – friendly. iii) Looking at the grading of the Char waste, it can be comfortably adopted for WMM, BM

and AC. iv) Since Char is used handled at lower temperature compared to conventional aggregates, it

results in precious energy points saving. v) Also since, less compaction is required there is less fuel consumption.

vi) Also, tests have shown its highly durable material.

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vii) Considering Char waste from quantum wise, quality wise and economical wise Char is on positive node.

References B. S. Hamad, Rteil. A. A. and Mutasseem, E. F., (2003) “Effect of used engine oil on properties and

hardened concrete”, Construction and Building materials, No. 17, 311-318. Hawkins, G. J., Bhatty, J. I and O’Hare, A. T.,(2003) “Cement kiln dust production, management and

disposal, Portland Cement Association”, R&D No. 2737. Indian Journal of Science and Technology, Vol. 3, August 2010. Indian Highways, May 2009. IS 2386 (Part 1) – 1997 IS 2386 (Part 3) – 1997 IS 2386 (Part 4) - 1997 Mroueh, U. M. and Wahlström, M., (2002) “By-products and recycled materials in earth

construction in Finland—an assessment of applicability”, Resources, Conservation and Recycling, No. 35, 17–129.

MoRTH: Specification for Road and Bridge Works. Nunes. M. C. M., Bridges. M. G., and Dawson. A. R., (1996) “Assessment Of Secondary Materials For

Pavement Construction: Technical And Environmental Aspects”, Waste Management, Vol. 16, Nos 1-3, 87-96.

National Cooperative Highway Research Program, Report 557. Okagbue, C. O. and Onyeobi. T. U.S.,(1999) “Potential of marble dust to stablise red tropical soils for

road construction”, Engineering Geology, No 53, 371-380. Sherwood, P. T., (1995) Alternative materials in road construction, Thomas Telford

Publications, London. Javed, S., Lovell, C. W., Leonard and Wood., W., (1994) “Waste foundry sand in asphalt concrete”

Transportation Research Record, TRB, National Research Council, Washignton, D. C., No. 1437, 27-34.

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BIOMEDICAL WASTE TREATMENT FACILITY

Sasmita Sahoo Government College of Engineering, Kalahandi, Bhawanipatna, India

Abstract: Biomedical waste has become a serious health hazard in many countries, including India. Careless and indiscriminate disposal of this waste by healthcare establishments and research institutions can contribute to the spread of serious diseases such as hepatitis and AIDS (HIV) among those who handle it and also among the general public. The issue of biomedical waste treatment facility has assumed great significance in recent times particularly in view of the rapid upsurge of HIV infection. The present scenario of biomedical waste (BMW) management in Indian hospitals is grim. Government of India has made proper handling and disposal of this category of waste a statutory requirement with the publication of gazette notification no 460 dated 27 July 1998. The provisions are equally applicable to our service hospitals and hence there is a need for all the service medical, dental, nursing officers, other paramedical staff and safaiwalas to be well aware of the basic principles of handling, treatment and disposal of biomedical waste. The present article deals with such basic issues as definition, categories and principles of handling, treatment and disposal of biomedical waste. It also describes about the precautious steps that can be taken for efficiently disposing the medical wastage to avoid infection. This article intends to create awareness amongst the personnel involved in health care services.

INTRODUCTION Everything is made for a defined purpose “anything which is not intended for further use is termed as waste”. In the scientific and industrial era combined with increasing population and their demand, the turnover of products has gone very high resulting into increase in quantum of urban solid waste. With increasing need of Health Care in fast changing society the role of hospitals/nursing homes comes to the forefront. Hospital is a residential establishment which provides short term and long term medical care consisting of observational, diagnostic, therapeutic and rehabilitative services for a person suffering or suspected to be suffering from disease or injury and for parturient.

• Historical Background

Hospital Waste or Health care waste should include any type of material generated in Health Care Establishments including aqueous and other liquid waste. Hospital waste means “Any solid, fluid or liquid waste material including its container and any other intermediate product which is generated during short term and long term care consisting observational, diagnostic, therapeutic and rehabilitative services for a person suffering or suspected to be suffering from disease or injury and for parturients or during research pertaining to production and testing of biological during immunization of human beings. Hospital waste includes garbage, refuse, rubbish and Bio Medical Waste”. "Bio-medical waste" means any waste, which is generated during the diagnosis, treatment or immunisation of human beings or animals or in research activities pertaining thereto or in the production or testing of biological.

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PRESENT SCENARIO

Waste management is one of the important public health measures. If we go into the historical background, before discovery of bacteria as cause of disease, the principle focus of preventive medicine and public health has been on sanitation. The provision of potable water, disposal of odour from sewage and refuse were considered the important factors in Prevention of epidemics.

Coming back to modern age, on the eve of 21st century with increased use of disposable material and the presence of dreaded disease like Hepatitis – B and AIDS, it is utmost important to take care of the infected and hazardous waste to save the mankind from disaster. The Health care institutions or hospitals which are responsible for care of morbid population are emitting voluminous quantity of rubbish, garbage and Bio Medical Waste matter each day from wards, operation theatre and outpatient areas. Proper management of hospital waste is essential to maintain hygienic, aesthetics, cleanliness and control of environmental pollution.

The hospital waste like body parts, organs, tissues, blood and body fluids along with soiled linen, cotton, bandage and plaster casts from infected and contaminated areas along with used needles, syringes and other sharps are very essential to be properly collected, segregated, stored, transported, treated and disposed of in safe manner to prevent hospital acquired infection. Various communicable diseases, which spread through water, sweat, blood, body fluids and contaminated organs, are important to be prevented. The Bio-Medical Waste scattered in and around the hospitals invites flies, insects, rodents, cats and dogs that are responsible for the spread of communication disease like plague and rabies. Rag pickers in the hospital, sorting out the garbage are at a risk of getting tetanus and HIV infections. The recycling of disposable syringes, needles, IV sets and other article like glass bottles without proper sterilization may be responsible for Hepatitis, HIV, and other viral diseases. It becomes primary responsibility of Health administrators to manage hospital waste in most safe and eco-friendly manner.

SOURCES OF BIOMEDICAL WASTE

Some of the sources of Biomedical waste are Hospitals, Medical Laboratories , Animal Houses, Home.

• Hazards of Biomedical / Health Care Waste

Hospital waste / health care waste includes all the waste generated by health care establishments, research facilities, and laboratories including minor or scattered source-such as care taken at home (Insulin Injection). About 75% to 90% of the waste produced by health care providers is non-hazardous “general waste” comparable to domestic waste.

BIOMEDICAL WASTE TREATMENT FACILITY

A Common Bio-medical Waste Treatment Facility (CBWTF) is a set up where bio-medical

waste, generated from a number of healthcare units, is imparted necessary treatment to reduce adverse effects that this waste may pose. The treated waste may finally be sent for disposal in a landfill or for recycling purposes. Installation of individual treatment facilities by small healthcare units requires comparatively high capital investment. In addition, it requires separate manpower and infrastructure development for proper operation and maintenance of treatment systems.

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The concept of CBWTF not only addresses such problems but also prevents proliferation of treatment equipment in a city. In turn it reduces the monitoring pressure on regulatory agencies. By running the treatment equipment at CBWTF to its full capacity, the cost of treatment per kilogram gets significantly reduced. Its considerable advantages have made CBWTF popular and proven concept in many developed country. The Bio-medical Waste (Management & Handling) Rules, 1998, gives an option to the bio-medical waste generator that such waste can also be treated at the common bio-medical waste treatment facility.

The second amendment of the rules in June, 2000, further eased the bottleneck in upbringing the CBWTF by making Local Authority responsible for providing suitable site within its jurisdiction. The concept of CBWTF is also being widely accepted in India among the healthcare units, medical associations.

LOCATION

A CBWTF shall be located at a place reasonably far away from residential and sensitive area so that it has minimal impact on these areas. The CBWTF shall be located as near to its area of operation as possible in order to minimize the travel distance in waste collection, thus enhancing its operational flexibility. The location shall be decided in consultation with the State Pollution Control Board (SPCB)/pollution Control committee (PCC). Sufficient land shall be allocated for CBWTF to provide all requisite systems. It is felt that a CBWTF will require minimum of 1 acre of land area. So, preferably, a CBWTF be set up on a plot size of not less than one acre. In any area, only one CBWTF may be allowed to cater up to 10,000 beds at the approved rate by the Prescribed Authority. A CBWTF shall not be allowed to cater healthcare units situated beyond a radius of 150km.

• Treatment Equipment

As per provisions of Bio-medical waste (Management & Handling) Rules, waste falling in most of the categories can be treated in systems based on non-burn technologies. Such waste account for about 90% of the total waste streams in a healthcare unit. A common Bio-medical Waste Treatment Facility (CBWTF) shall have following treatment facilities;

• Incineration

It is a controlled combustion process where waste is completely oxidized and harmful microorganisms present in it are destroyed under high temperature. The guide lines for “Design & Construction of Bio-medical Waste Incinerators” prepared by CPCB shall be followed for selecting/installing a better bio-medical waste incinerator.

• Autoclaving

Autoclaving is a low heat thermal process where steam is brought into direct contact with waste in a controlled manner and for sufficient duration to disinfect the wastes. For ease and safety in operation, the system should be horizontal type and exclusively designed for the treatment of bio-medical waste. For optimum results, pre-vacuum based system be preferred against the gravity type system. It shall have tamper-proof control panel with efficient display and recording devices for critical parameters such as time, temperature, pressure, date and batch number etc.

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• Hydroclaving

Hydroclaving is similar to that of autoclaving except that the waste is subjected to indirect heating by applying steam in the outer jacket. The waste is continuously tumbled in the chamber during process.

Though chemical disinfection is also an option for the treatment of certain categories of bio-medical waste but looking at the volume of waste to be disinfected at the CBWTF and the pollution load associated with the use of disinfectants, the use of chemical disinfection for the treatment of bio-medical waste at CBWTF is not recommended.

• Microwaving

In micro-waving, microbial inactivation occurs as a result of the thermal effect of electromagnetic radiation spectrum lying between the frequencies 300 and 300,000Mhz. Microwave heating is an inter-molecular heating process. The heating occurs inside the waste material in the presence of steam.

• Shredder

Shredding is a process by which waste are cut into smaller pieces so as to make the wastes unrecognizable. It helps in prevention of reuse of bio-medical waste and also acts as identifier that the wastes have been disinfected and are safe to dispose off. A shredder to be used for shredding bio-medical waste shall confirm to the following minimum requirements:

• The shredder for bio-medical waste shall be of robust design with minimum maintenance requirement.

• The shredder should be properly designed and covered to avoid spillage and dust generation. It should be designed such that it has minimum manual handling.

• The hopper and cutting chamber of the shredder should be so designed to accommodate the waste bag full of bio-medical waste.

• The shredder blade should be highly resistant and should be able to shred waste sharps,

syringes, scalpels, glass vials, blades, plastics, catheters, broken ampoules, intravenous sets/bottles, blood bags, gloves, bandages etc.

It should be able to handle/shred wet waste, especially after microwave/autoclave/hydroclaved. The blade shall be of non-corrosive and hardened steel.

INFRASTRUCTURE

The CBWTF should have enough space within it to install required treatment equipment,

incoming and outgoing waste storage area, vehicle-parking and washing area, Effluent Treatment Plant (ETP), staff room etc. The required area for CBWTF would depend upon the projected amount of bio-medical waste to be handled by it. A CBWTF shall have the following infrastructure:

• Treatment Equipment Room

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A separate housing is provided for each treatment equipment at the CBWTF such as incinerator room, autoclave room, microwave room etc, as applicable. Each room should have well-designed roof and walls. Such room shall be well ventilated and easy to wash. The floor and interior finishing of the room shall be such that chances of sticking of micro-organisms are minimized. This can be attained by providing smooth & fine floor and wall surfaces ( to a height of 2 metre from floor ) preferably of tiles. The number of joints in such surfaces shall be minimal.

• Main Waste Storage room

This should be provided near the entry point of the CBWTF to unload and store all biomedical wastes that have been transported to the facility by vehicle. The size of the room should be adequate to store all wastes transported to the CBWTF. The front portion of the room shall be utilized for unloading the wastes from the vehicle and back or side portion shall be utilized for shifting the wastes to the respective treatment equipment. In the front of the room where vehicle is parked for unloading, the floor shall be made impermeable so that any liquid spilled during unloading does not percolate into the ground. The liquid generated during handling of wastes and washing, shall be diverted to the inlet of ETP.

In the main storage room, wastes shall be stacked with clear distinction as per the color

coding of the containers. From here, the colored containers may be sent to the respective treatment equipment. The main storage room too small has provisions similar to that of equipment room such as roofing, well ventilated, easy to wash floors & walls, smooth and fine surfaces etc.

• Treated Waste Storage room

This is the room where wastes treated in different treatment units shall be stored. The wastes shall be stored in separate group as per the disposal options. Other provisions in the room shall be similar to the main storage room.

• Generator Set

Every CBWTF shall have generator set as standby arrangement for power, with sufficient capacity to run the treatment equipment during the failure of power supply. The generator set shall comply with the necessary requirements under the Environment (Protection) Rules, 1986.

• Sign Board

An identification board of durable material and finish shall be displayed at the entrance to the facility. This shall clearly display the name of the facility, the name, address and telephone number of the operator and the prescribed authority, the hours of operation and the telephone numbers of the personnel to be contacted in the event of an emergency.

RECORD KEEPING

A well-maintained record of all the activities at the CBWTF also enables the facility operator to produce all information of the activities on demand of the concerned Authority. The record should include all information related to each activity at the CBWTF site. Minimum requirement for record keeping are:

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• Records of Waste Movements

Daily records shall be maintained for the waste accepted and treated waste removed from the sites which include the minimum details:

Waste accepted: Waste collection date, name of the healthcare unit, and waste category as per the rules, quantity of waste, vehicle number and receiving date.

Treated waste removed: date, treated waste type, quantity, vehicle number and location of disposal.

• Logbook for the Equipment

A logbook is maintained for each treatment equipment installed at the site and include the following:

1. The weight of each batch. 2. The categories of waste as per the rules. 3. The time, date, and duration of each treatment cycle and total hours of operations. 4. The complete details of all operational parameters during each cycle. • Site Records

Site records include the following: 1. Details of construction or engineering works 2. Maintenance schedule, breakdowns/trouble shootings and remedial actions 3. Emergencies 4. Incidents of unacceptable waste received and the action taken 5. Details of site inspections by the officials of the regulatory agency and necessary action

on the observations 6. Daily, monthly and annual summary records should be maintained and made available at

the site for inspection whenever required by an authorized officer of regulatory agency.

COLLECTION OF BIOWASTE The collection of bio-medical waste should be carried out to avoid any possible hazard health

and environment. Generator of the bio-medical waste is responsible for providing segregated waste to the CBWTF operator. The wastes shall be segregated as per the provisions of the Bio-medical waste (Management & Handling) Rules, 1988. The CBWTF operator shall not accept the non-segregated waste and such incident shall be reported to the prescribed Authority. Temporary storage at healthcare unit shall be designated. The coloured bags handed over by the healthcare units shall be collected in similar coloured containers with cover. Each bag shall be labeled as per the Schedule III & Iv of the Bio-medical waste (Management & Handling) Rules, so that at any time, the healthcare units can be traced back that are not segregating the bio-medical waste as per the Rules. The coloured containers should be strong enough to withstand any possible damage that may occur during loading, transportation or unloading of such containers.

These containers shall also be labeled as per the Schedule of the Rules. To maintain the records such as name of the healthcare unit, the type and quantity of waste received, signature of the authorized person from the healthcare unit side, day and time of collection etc.

TRANSPORTATION

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The bio-medical waste collected in coloured containers shall be transported to the CBWTF in a fully covered vehicle which shall be dedicated for transportation of bio-medical waste only. Depending upon the volume of the wastes to be transported, the vehicle may be a three wheeler, light motor vehicle or heavy duty vehicle. Depending upon the area to be covered under the CBWTF, the route of transportation shall be worked out. The transportation routes of the the vehicle shall be designed for optimum travel distance and to cover maximum number of healthcare units. As far as possible, the transportation shall be carried out during non-peak traffic hours. If the area to be covered is very large, a satellite station may be established to store the bio-medical waste collected from the adjoining areas.

Table 1: Disposal of treated biomedical waste

S No. Waste category Disposal method

1 Plastic wastes after disinfection and shredding

Recycling or municipal landfill

2 Disinfected sharps (except syringes) (a) If encapsulated (b) If non-encapsulated

Municipal landfill Municipal landfill/possibility of recycling shall be explored

3 Incineration ash Secured landfill 4 Other treated solid wastes Municipal landfill 5 Oil and grease Incineration 6 Treated waste water Sewer/drain or recycling

The wastes stored at satellite station be transported to the CBWTF in a big vehicle. It shall be

ensured that the total time taken from generation of bio-medical waste to its treatment, which also includes collection and transportation time, shall not exceed 48 hours. The vehicle must posses the following:

1. Separate cabins shall be provided for driver/staff and the biomedical waste containers. 2. The base of the waste cabin shall be leak proof to avoid pilferage of liquid during

transportation. 3. The waste cabin may be designed for storing waste containers in tiers. 4. The waste cabin shall be so designed that it is easy to wash and disinfect. 5. The inner surface of the waste cabin shall be made of smooth surface to minimize water

retention. 6. The waste cabin shall have provisions for sufficient opening in the rear and/or sides so

that waste containers can be easily loaded and unloaded. 7. The vehicle shall be labeled with the biomedical waste symbol and should display the

name, address and telephone number of the CBWTF.

COST CHARGED FROM THE HEALTHCARE Cost to be charged from the healthcare units plays an important role in sustaining the project.

The cost shall be so worked out that neither it becomes a monopoly of the CBWTF operator nor the interest of the CBWTF operator is overlooked. It is recommended that cost to be charged from the healthcare units shall be worked out in consultation with the State Pollution Control Board/Pollution Control Committee and local Medical Association.

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RESPONSIBILITIES All departments that generate infectious waste will ensure the proper procedures in the

program. Individual departments will be responsible for the infectious waste generated and stored in their department until transport by UH Environmental Services or the approved infectious waste management contractor. All infectious waste generators will be responsible for the following unless otherwise noted:

1. Transport of infectious waste to a local, secure storage area. 2. Ensure that the storage area is kept clean.

CONCLUSION The hospital waste, in addition to the posing risk to the patients and personnel who handle

these wastes, is also a threat to the public health and Environment. It is emerging as a health hazard to the community at large. Keeping in view, in appropriate management of bio-medical wastes, the Ministry of Environment and Forests notified the “Bio-medical waste (Management and Handling) Rules 1998.” These rules are meant to protect the society, patients and health care workers. The most imperative component of the waste management plans is to develop a system and culture through education, training and persistent motivation of the healthcare staff.

References

National Guidelines on Hospital Waste Management based upon the Biomedical Waste

(Management and Handling) Rules, (1998) Park K., (2005), Hospital Waste Management Park’s Textbook of Preventive and Social Medicine,

M/s Banarasidas Bhanot Publications, New Delhi. 18th Edition, pp 595-598 Rao S.K.M., Ranyal R.K., Bhatia S.S., Sharma V.R., (2004), Bio-Medical Waste Management: an

Infrastructural survey of Hospitals, MJAFI, 60(4), 379-382 Sharma M. Hospital Waste Management and its Monitoring. Jaypee Brothers, New Delhi. 1st

Edn. 2002 Singh I.B., Sharma R.K., (1996), Hospital Waste Disposal system and Technology, Journal of Academy of Hospital Administration. July, 8(2), 44-48

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EFFECT OF REINFORCEMENT ON FLY ASH SLOPE

Parveen Chander*, Jasbir Singh1, Rajesh Kumar* and JN Jha2 * Department of Civil Engineering, P.T.U. G.Z.S. Campus, Bathinda.

1Department of Civil Engineering, Ramgarhia PolytechnicCoolege Phagwara. 2Department of Civil Engineering, Guru Nanak Dev Engineering College, Ludhiana.

Abstract: It is shown that the load-settlement behaviour and ultimate bearing capacity of the footing can be considerably improved by the inclusion of a reinforcing layer at the appropriate location in the fill slope. The results of a series of plane strain model tests carried out on reinforced/ unreinforced fly ash slopes loaded with a rigid strip footing. Optimization of finite element plane strain two-dimensional model is done for embedment, edge distance, geogrid length and slope angle, using the computer program PLAXIS. The effect of single layer of geo-grid reinforcement in improving the load carrying capacity of such slopes, the effect of other variables such as reinforcement location, edge distance, slope angle and reinforcement length have also been investigated in detail. The main objective of this study is to determine the influence of geosynthetics reinforcement on the bearing-capacity characteristics of the footing on slope and to suggest an optimum geometry of reinforcement placement. The results of plane strain PLAXIS model and prototype PLAXIS models have been compared with experimental results of small scale model from existing literature. The results obtained from the proposed analysis show good agreement with the experimental results and therefore may be used in actual practical problems for design of reinforced slopes loaded with a surcharge at its top.

Key words: Single layer of reinforcing, Numerical Modeling, Bearing capacity, Flyash slope, Embedment, Geogrid.

INTRODUCTION se of polymeric reinforcements to improve load-bearing capacity of foundation has been extensively reported by researchers by using different foundation material. These investigations have demonstrated that both the ultimate bearing capacity and settlement characteristics of the foundation can be improved by the inclusion of reinforcements within the fill. One of the possible solutions to improve the bearing capacity would be to reinforce the sloped fill with the layer or layers of geo-grid.

Henry Vidal (1969) introduced the concept of reinforced earth and patented it with reference to its usefulness to practical problems in 1968. After that a lot of research was carried out to understand the concept, mechanism and behavior of reinforced soil. Yang, Z (1972) hypothesized that the tensile stresses built up in the reinforcements were transferred to the soil through sliding friction and caused an increase in the confining pressure. It is assumed that when failure is caused by slip between the soil and the reinforcements, the reinforcing effect can be expressed in terms of an increased apparent friction angle. Concept of using a single layer of reinforcing was developed by Andrawes et al in 1983, and optimum depth of placement, its length were established by McGown, A. et al. in 1978 and Patel. N.M. et al. in 1981. The finite element analysis is based on a

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quasi-elastic continuum mechanics approach in which stresses and strains are calculated. The Mohr-Coulomb model is a well-known model, used by many investigators, (Lee and Manjunath, 2000, Patra, C.R., Das, B.M. and Saeed Alamshahi, Nader Hataf, 2009). The model involves mainly five parameters, Young’s modulus (E), Poisson's ratio (ν), the cohesion (C), the friction angle (φ), and the dilatancy angle (ψ). The modeling of all the cases is done using this model.

Authors have validated the experimental data reported by Chaudhry, et al (2010) using plane strain finite element PLAXIS modeling. Proto type modeling (ten times the experimental model) has also been done using PLAXIS software. The fill material (flyash) and other materials and their properties are kept same as used in experimental study. The present paper therefore aims at a comprehensive study of the various parameters that affect the behavior of strip footing on un-reinforced/reinforced flyash slope with single layer geo-grid placed at different depths from the top of the fly ash slope under external loading in the form of foundation load. The effect of other variables such as edge distance, reinforcement length and slope angle, has also been investigated in detail.

EXPERIMENTAL STUDY BY THE INVESTIGATOR (Chaudhry et al, 2010)

The rigid foundation was modeled by footings made of well-seasoned best quality Sal wood. The model footings of size 30cm x 10cm (L/B>2), were used for conducting the model tests. The thickness of all the model footings was 75mm. The bases of the footings were knurled to simulate the rough base condition of a prototype footing.

750m

m

Bed of testtank

compacted fly ash

Soil slope

ReinforcementFooting

Side wall of test tank

L

BDe

Z

r

Load

Fig 1: Experimental Model

Table 1: Variables of experimental study (Chaudhry et al, 2010)

Sl. No.

Footing width, B (mm)

Embedment Ratio (Z/B)

Edge Distance ‘De’

Slope Angle ‘β’ (in degrees) 1

. 100 U.R 1B, 2B, 3B 450, 600

2.

100 0.25 1B, 2B, 3B 450, 600 3

. 100 0.50 1B, 2B, 3B 450, 600

4.

100 0.75 1B, 2B, 3B 450, 600 5

. 100 1.00 1B, 2B, 3B 450, 600

6.

100 1.50 1B, 2B, 3B 450, 600

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7.

100 2.00 1B, 2B, 3B 450, 600 8

. 100 2.50 1B, 2B, 3B 450, 600

9.

100 3.00 1B, 2B, 3B 450, 600

NUMERICAL MODELING AND ANALYSIS USING PLAXIS

PLAXIS is a finite element package that has been developed specifically for the analysis of deformation and stability in geotechnical engineering projects. There are various models available in PLAXIS software. In the present study, Material properties used were same as in experimental study. The results obtained from experimental studies (Chaudhry et al, 2010) were verified by carrying out numerical analysis using the finite element method. The plane strain elastoplastic finite element analysis was carried out using the commercial software program PLAXIS (Brinkgreve and Vermeer 1998). In this study, the modeling was done using Mohr-Coulomb model.

Table 2: Properties of fly ash

Property Unit Value

Flyash unit weight above phreatic level γunsat [kN/m³] 13.82 Flyash unit weight below phreatic level γsat [kN/m³] 16.00 Young’s modulus Eref [kN/m²] 8000 Poisson's ratio µ [-] 0.38 Shear modulus Gref [kN/m²] 2898.55 Young's modulus Eoed [kN/m²] 14975.84 cohesion cref [kN/m²] 20.00 friction angle φ [°] 14.00 dilatancy angle ψ [°] 0.00 Interface strength Rinter. [-] 0.55

Table 3: Properties of footing

Table 4: Properties of Geo-grids

OUTPUT DATA POST- PROCESSING

After the generation of a finite element model, the actual finite element calculations have been executed. The main output quantities of a finite element calculation are the displacements at the nodes and the stresses at the stress points. In addition, when a finite element model involves structural elements, structural forces are calculated in these elements. Fig 2 through 5 is some typical presentations obtained as Output. The geometry of a typical finite element model adopted for the analysis is shown in Fig. 2. The soil parameters adopted for the flyash layer was assumed to remain the same in all the finite element analyses for the unreinforced system. For

Identification Normal Stiffness, EA [kN/m]

Flexural Rigidity, EI [kNm²/m]

Equivalent thickness, D mm

Wooden Footing 88200.00 36.01 70

Identification Normal stiffness EA [kN/m] GEOGRID 4.00

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the reinforced case, a reinforcement layer was introduced at the required depth with appropriate strength reduction factors between the contact surfaces and stiffness of the reinforcement entered as additional parameter. Finite element analyses were carried out by applying vertical prescribed displacements and horizontal prescribed displacements are kept zero to the nodes at the base of the footing. The specified footing displacement was applied in equal increments of 100 steps. The large strain effect was modeled by upgrading the nodal coordinates and stiffness matrix after each incremental step. The footing pressure was calculated by dividing the resulting vertical nodal loads at the base of the footing by the width of the footing. The results obtained from the model tests are in close agreement with those from the analyses. The finite element calculations are fairly accurate for the computed values of ultimate bearing capacity (the ultimate bearing capacity obtained from the finite element analyses was defined in the same way as that defined in the model tests). The results of the finite element analyses confirm the experimental value in terms of the optimum embedment depth to footing width ratio of the reinforcement layer (Z/B = 1.0) which results in maximum ultimate bearing capacity.

Fig.2: Plot of typical geometry model with significant nodes.

. Fig 3: Typical case of deformed mesh.

• Pressure- Settlement Curve

The Curves program can be used to draw Pressure settlement curve. A typical pressure-settlement curve is shown in Fig. 4. The values of bearing capacity for different cases has been calculated from curves drawn using double tangent method.

x

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Fig 4: Typical pressure-settlement curve (optimum case)

RESULTS AND DISCUSSION

Model tests were carried out on model plane strain footing supported on flyash slope. The effect of geogrid parameters on the ultimate load and displacement were obtained and discussed. An additional numerical study on the effect of the behavior of a prototype footing was carried out using the finite element model. The numerical results obtained using the finite element model correlated well with the experimental results as discussed earlier. However, to supplement these results and to further investigate the behaviour of a strip footing resting on a reinforced flyash slope over a range of parameters, that were not investigated in laboratory model tests, an additional parametric study was carried out. The main aim of this parametric study was to establish the reliability of model test results to develop design recommendations with regard to the optimum values of reinforcement embedment depth, length of reinforcement, edge distance and slope angle for deriving the maximum bearing capacity. To investigate the optimum length of reinforcement layer, a parametric study was carried out at different reinforcement embedment depth (Z/B), length of reinforcement to footing width ratios (LR/B), the edge distance to footing width ratio (De/B) and slope angle (300,450,600). The length of reinforcement was always measured from the face of the slope.

• Effect of Embedment Ratio (Z/B) on Bearing Capacity

The effect of embedment ratio (Z/B) on bearing capacity has been investigated using PLAXIS and the values obtained from the PLAXIS analysis are compared with the experimental results (Fig.5). The trends of the effect of embedment ratio (Z/B) on bearing capacity ratio are similar to experimental trends. The maximum value of ultimate bearing capacity of 128 kPa has been obtained for an embedment ratio, Z/B, equal to1.0. It was observed that the ultimate bearing capacity and BCR values for Z/B ratio less than or greater than 1.0 are decreasing. The analytical results obtained from PLAXIS are in good agreement with the experimental results.

0 3 6 9 12 15-0.02

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Fig 5: Effect of Embedment Ratio. • Effect of Edge Distance Ratio (De/B) on Bearing Capacity

As shown in Fig.6, the experimental test results data show increase in bearing capacity with increase in edge distance from 1.0B to 3.0B and it was reported by the Investigators that when edge distance increased beyond 3.0B, the increase in ultimate bearing capacity is marginal and it approaches almost equal to that of the footing on level ground. The trend shown by analytical results is similar to that of the trend reported in the experimental investigation. An increase (14.06%) in bearing capacity with increase in edge distance from 1.0B to 3.0B and a decrease (20.31%) in the bearing capacity is obtained when edge distance is reduced from 1.0B to 0.5B. Further investigation has been carried by keeping the edge distance as 1.0B.

Fig 6: Effect of Edge Distance Ratio,

• Effect of Geogrid Length Ratio (L/B) on Bearing Capacity

The effect of length of geogrid has not been investigated by Choudhry, et al (2010). In the present investigation, the effect of length of the geogrid has been studied considering the optimum value of Embedment Ratio (Z/B) and Edge Distance Ratio (De/B). The results show (Fig.7) that there is an optimum value for the length of reinforcement at which maximum bearing capacity can be derived. Below the footing there exists a zone of shear deformation of soil, and only the portion of reinforcement which lies within this zone will have its tensile strength effectively mobilized. Portions of the reinforcement away from the slope face would serve as anchorage to provide pullout resistance to the geo-reinforcement. Therefore, the total required length of the reinforcement located underneath the footing and the anchorage is 7B for numerical analysis results.

Fig 7: Effect of Geogrid Length Ratio.

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The trend shows that the increase in bearing capacity is marginal (3.90%) when the geogrid length is increased from 7B to 11B, whereas, the value of bearing capacity decreased by 21.88% when the geogrid length is decreased from 7B to 3B. Therefore, the optimum length of the geogrid has been kept as 7B for further investigation.

• Effect of Slope Angle (β) on Ultimate Bearing Capacity

The experimental test results have been reported by investigators for two different slope angles only viz. 45o and 60o. Authors reported that for a given edge distance and embedment ratio, the ultimate bearing capacity value decreases with the increase in slope angle. In the numerical analysis three slopes have been considered for better analysis predictions viz. 30o, 45o and 60o. For the investigation of slope effect, the optimum embedment ratio (Z/B) equal to 1.0B, edge distance ratio (De/B) of 1.0B and geogrid length ratio of 7.0B has been considered. The results obtained from the PLAXIS output have been compared and shown as Fig 8. The same trend as that of experimental results has been observed.

Fig 8: Effect of Slope Angle.

It has been observed from that the ultimate bearing capacity value decreases with the increase in slope angle.

• Scale effect on Bearing Capacity

The effect of size of model on bearing capacity have been investigated using PLAXIS for all embedment ratios (Z/B) and the values obtained from the PLAXIS analysis are compared with the PLAXIS model and experimental results in Fig.10 and effect of size on bearing capacity ratio has been compared in Fig. 11. The maximum value of ultimate bearing capacity of 118 kPa has been obtained for an embedment ratio, Z/B is equal to1.0. It has also been observed that the ultimate bearing capacity and BCR values decreases with Z/B ratio less than or greater than 1.0. Fig. 9 and 10 show that the analytical results obtained from PLAXIS model shows a good agreement with the experimental results and the results shown by full scaled PLAXIS model are conservative. The ultimate bearing capacity ratio for PLAXIS model and full scaled PLAXIS model (Prototype) is similar and on conservative side, compared with the experimental results. It has been concluded from this study that the PLAXIS models can directly be used for analysis of actual practical problems.

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Fig. 11 Size effect on ultimate bearing capacity ratio.

CONCLUSIONS

A series of numerical model tests has been carried out to evaluate the ultimate bearing capacity of a strip footing resting on geo-grid reinforced fly ash slopes. The study primarily aimed at to validate experimental study deter-mining the effect of geo-grid reinforcements and its location on the ultimate bearing capacity and settlement characteristics of such footings. Results obtained from the present investigation are compared with experimental results from existing literature (Chaudhary et al, 2010). Based on comparison of experimental and numerical results, the following conclusions are made:

A good agreement between the experimental and numerical results on general trend of behavior and the critical values of the geo-grid parameters is observed.

The load carrying capacity of the footing resting on top of a fly-ash slope is low but insertion of a geo-grid reinforcement layer at suitable location within the sloped fill considerably improves the load carrying capacity of footings located on such slopes. The effectiveness of geo-grids in improving the bearing capacity of footings on slopes is attributed to its primary properties such as aperture size and axial stiffness.

The optimum embedment depth of the single reinforcement layer which resulted in the maximum ultimate bearing capacity of the geo-grid-reinforced slope was about 1.0 (Z/B=1.0) times the width of the footing.

The ultimate bearing capacity of the footing on both reinforced and un reinforced slopes increases with an in-crease in edge distance ,for edge distances of 0 to 3B. However, at an edge distance greater than 2B, the ultimate bearing capacity of the footing does not increase much to be affected by the presence of the slope.

The bearing capacity of footing reduces with increase in slope angle for both the cases i.e. un-reinforced slope as well as reinforced slope.

The ultimate bearing capacity of the footing with optimum edge distance and embedment ratio increases with an in-crease in length of geo-grid from 3B to 11B. However, at a geo-grid

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length greater than 7B, the ultimate bearing capacity of the footing does not increase much to be affected by the geo-grid length.

Small scale model footing is much smaller as compared to that under a full scale footing. The low stress level in granular soils corresponds to a greater angle of internal friction when compared to the angle of friction at higher stress level. Therefore, the average shear strength mobilized along a slip line under a foundation decreases with increase in foundation size due to decrease in the angle of internal friction.

The general trend of model study indicated the benefits on the behavior of footing resting at the top of a reinforced fly-ash slope and provides a useful basis for conducting full scale model tests leading to an increased understanding of the real behavior and application of soil reinforcement particularly when fly-ash is used as a fill material.

In general, flyash can be successfully used as an embankment fill material and fly-ash slopes could be made to stand at slopes steeper than the angle of internal friction of fly-ash.

References

Andrawes, K.Z, (1982), "The Finite Element Method of Analysis Applied to Soil Geotextile Systems", Proc. 2nd International Conference on Geotextiles, Las Vagas,Vol.3, pp.695-700.

Andrawes, K.Z., McGowan, A. and Wilson-fahmy, R.F. (1983), "The Behaviour of a Geotextile Reinforced Sand Loaded by a Strip Footing", Proc.8th European Conference on Soil Mechanics and Foundation Engineering, Helsinki, Vol.1, pp.329-334.

Choudhary,A.K., Jha, J.N. Gill, K.S. (2010) “Laboratory investigation of bearing capacity behaviour of strip footing on reinforced fly Ash slope” a journal published by Elsevier.

Hausman, M. R. and Lee, I.K. (1976), "Strength Characteristics of a Reinforced Soil", Proc. International Symposium on New Horizons in Construction Material, Lehigh.

Hausman, M.R. (1990), "Engineering Principles of Ground Modifications", McGraw Hill Publishing Co., New York.

Huang, (1994) "Failure Mechanism of Reinforced Sand Slopes Loaded with a Footing", Soils and Foundations, Vol.34, No. 2, pp.27-40.

Huang, (1994) "Stability Analysis for Footings on Reinforced Sand Slopes", Soils and Foundations, Vol.34, No.3, pp.21-37.

Kaniraj, S.R. and Gayathri, V. (2001), "Geotechnical Behaviour of Fibre Reinforced Fly Ash" Proc. International Symp. on 'Earth Reinforcement', Fukuoka, Japan, pp.61-65.

Lee, K.M., Manjunath, V.R., 2000. Experimental and numerical studies of geo- synthetic-reinforced sand slopes loaded with a footing. Canadian Geotechnical Journal 37, 828-842.

McGown, A, (1978), "Effect of Inclusion Properties on the Behaviour of Sand", Geotechnique, 28, No.3, pp.327-346.

Patel, N.M. (1983), "Some Parametric Studies on Reinforced Sand Bed", Proc. Indian Geotechnical Conference, Madras, India, pp.V-13-V-17.

Patel, N.M., Paldas, M. and Verdarajan, A. (1981), "New System of Reinforcing the Foundation Sand Beds", Proc. Geomech-81, Hyderabad, pp.169-171.

Patra, C.R., Das, B.M., Atalar, C., 2005. Bearing capacity of embedded strip foundation on geogrid-reinforced sand. Geotextiles and Geomembranes 23 (5), 454-462.

Rowe, R.K. (1987), "Geotextile Reinforcement on the Design of Low Embankments on Very Soft/Weak Soils", Technical Report PR. 239, Ontorio Ministry of Transportation and Communications, Canada.

Saran, S. (1989), "Bearing Capacity of Footings Adjuscent to Slopes", Journal, Geotech. Div. ASCE, Vol.115, No.4, pp.553-573.

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Saeed Alamshahi, Nader Hataf , (2009), Geotextiles and Geomembranes, Elsevier,217-226. Shields, D., Chandler, N. and Garnier, J. (1990), "Bearing Capacity of Foundations in Slopes",

Journal Geotech. Div., ASCE, Vol.116, No.3, pp.528-537. Singh, T.K. (1986), "Some Studies on Bearing Capacity and Stability of Slopes", Ph. D.

Dissertation Submitted to I.I.T., Kharagpur, India. Sud, V.K., Saran, S. and Handa, H.C. (1985), "An Experimental Study of Shallow Foundations

Adjacent to Slopes", Indian Geotechnical Conference, Roorkee, Vol.1. Uchida, I. and Hirata, T. (1974), "Experiments on the Failure of Embankment Under Surcharges",

Proc. 9th Research Meeting of JSSMEF, pp.509-512. Vidal, H. (1969), "The Principle of Reinforced Earth", Highway Research Record, No.282, pp.1-

16. Wu, J.T.H., Siel, B.D., Chou, N.N.S., and Helway, H.B. (1992), "The Effectiveness of Geosynthetic

Reinforced Embankments Constructed Over Weak Foundations", Geotextile and Geomembranes, 11, pp.133-150.

Yang, Z. (1972), "Strength and Deformation Characteristics of Reinforced Sand" Ph.D. Dissertation, Univ. of California, Los Angeles, California.

385

EXPERIMENTAL INVESTIGATIONS ON SELF- COMPACTING CONCRETE USING

BRICK DUST AND COAL ASH AS FINE AGGREGATE REPLACEMENT

Kanwar Jeet Singh Bedi and Rakhjinder singh* Department of Civil Engineering, Guru Nanak Dev Engineering College, Ludhiana

*Department of Civil Engineering, GGI, Ludhiana

Abstract: In recent years, Self Compacting Concrete (SCC) has gained a wide use for placement in congested reinforcement concrete structures where casting conditions are difficult and in high rise buildings where pump ability properties are required. For such applications the fresh concrete must possess high fluidity and good cohesiveness. The use of fine materials such as Coal ash and Brick dust and super plasticizer (S.P) can ensure the required concrete properties. In this experimental it has been tried to replace Fine aggregates with Coal Ash (CA) and Brick Dust (BD) which is a waste material. Availability of aggregates is limited, while on the other side CA and BD are dumped as a waste. Their use as a partial or full replacement of fine aggregate in SCC can make the concrete construction more sustainable and environment friendly.

INTRODUCTION

Self Compacting Concrete as the name implies is the concrete requiring no vibration to fill the form homogeneously. Self Compacting Concrete (SCC) is defined by two primary properties. Ability to flow or deform under its own weight and the ability remain homogeneous while doing so. Flow ability is achieved by utilizing high proportion of water reducing admixtures and segregation resistance is ensured by introducing a chemical called viscosity modifying admixture (VMA) or increasing the amount of fines in the concrete. The study focuses on comparison of SCC containing varying amounts of brick dust and marble powder. In recent years, self compacting concrete has gained a wide use for placement in congested reinforcement concrete structures where casting conditions are difficult and in high rise buildings where pump ability properties are required.

• Material Aspects of Self Compacting Concrete

Self-consolidating concrete is designed to meet specific applications requiring high deformability, high flow ability and high passing ability. The rheological properties and robustness of SCC vary in a wide range. It is more susceptible to changes than ordinary concrete because of a combination of detailed requirements, more complex mix design and inherent low yield stress and viscosity. Variations in properties (and robustness) are attributed therefore to the specific effects of the ingredients on the rheological properties of the mixture, effects of the physical properties (i.e. size and specific density) of the aggregate and the mixing history. Aggregates, cement, water and HRWR are the principal materials of SCC where as SCM, VMA and other chemicals can be used as the optional materials. The brief illustration of component materials of SCC is given below.

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• Coarse Aggregate

Coarse aggregates significantly influence the performance of SCC by affecting the flowing ability, segregation resistance, and strength of concrete. The nominal maximum size for SCC can be 20 or 25 mm. However, the smaller size is preferable to produce higher strength and to reduce segregation in fresh SCC. Round aggregates are better than angular aggregates for flowing ability of SCC while rough and angular aggregates are conducive to high strength and strong interfacial bond due to rough surface texture and interlocking characteristic. The gradation of coarse aggregates affects the flow properties and segregation resistance of SCC. The well-graded coarse aggregates contribute to produce the optimum mixture with least particle interference and thus enhance the flowing ability and reduce the tendency of segregation in fresh concrete. They also improve the hardened properties and durability of concrete due to dense particle packing.

• Fine aggregate

Fine aggregates increase the flowing ability and segregation resistance when used at a suitable amount. In addition, they modify the strength of concrete when used in varying proportion with cement and coarse aggregates. Particle shape, surface texture, surface area and void content affect the mixing water requirement and compressive strength of concrete .The fine aggregates for SCC should be sharp, angular, chemically inert, sound, low absorbent and free from deleterious substances to attain high strength and good durability. Well-graded fine aggregates increase the flow of mortar and hence may improve the flowing ability of SCC. Furthermore, the well-graded fine aggregates contribute to improve the packing density and thus the hardened properties and durability of concrete. A fineness modulus in the range of 2.5 to 3.2 is generally recommended for SCC.

Cement Portland cement is most widely used to produce various types of concrete. The cement used for SCC should have sound flow and setting properties. It should enhance the fluidity of concrete and should be compatible with the chemical admixtures such as HRWR and VMA. The cement should possess carefully controlled fineness, and should produce low or moderate heat of hydration to control the volume changes in concrete.

• Brick Dust

Brick dust is a waste product obtained from different brick kilns and tile factories. There are numerous brick kiln which have grown over the decades in an unplanned way in different part of the country. Tons of waste products like brick dust or broken pieces or flakes of bricks (brickbat) come out from these kilns and factories. So far, such materials have been used just for filling low lying areas or are dumped as waste material.

• Coal Ash

The fly ash produced from the burning of pulverized coal in a coal-fired boiler is a fine-grained, powdery particulate material that is carried off in the flue gas and usually collected from the flue gas by means of electrostatic precipitators, bag houses, or mechanical collection devices such as cyclones.

387

In general, there are three types of coal-fired boiler furnaces used in the electric utility industry. They are referred to as dry-bottom boilers, wet-bottom boilers, and cyclone furnaces. The most common type of coal burning furnace is the dry-bottom furnace.

When pulverized coal is combusted in a dry-ash, dry-bottom boiler, about 80 percent of all the ash leaves the furnace as fly ash, entrained in the flue gas. When pulverized coal is combusted in a wet-bottom (or slag-tap) furnace, as much as 50 percent of the ash is retained in the furnace, with the other 50 percent being entrained in the flue gas. In a cyclone furnace, where crushed coal is used as a fuel, 70 to 80 percent of the ash is retained as boiler slag and only 20 to 30 percent leaves the furnace as dry ash in the flue gas.

• Viscosity modifying admixture (VMA)

VMA improves the viscosity and cohesion of fresh concrete and thus reduces the bleeding, surface settlement and aggregate sedimentation resulting in a more stable and uniform mix. The mechanism of viscosity enhancement depends on the type of Objectives of Study.

• Super Plasticizer

Super plasticizer deflocculates the cement particles and frees the trapped water by their dispersing action, and hence enhances the flowing ability of SCC. In dispersing action, the inter-particle friction and thus the flow resistance are also decreased, and therefore the flowing ability of concrete is improved. High-range water reducers can either increase the strength by lowering the quantity of mixing water for a given flowing ability, or reduce both cement and water contents to achieve a given strength and flowing ability.

PRESENT WORK

The present work deals with the development of SCC by replacing fine aggregate with brick dust and coal ash. Various SCC mixes were produced first by replacement of fine aggregate with coal ash and then with brick dust in varying percentages of 25%, 50%, 75%, 25% and 100% respectively along with addition of VMA and HRWR. Fine aggregate was also replaced jointly by the combination of BD and CA. The fresh SCCs were tested for filling ability and passing ability. After mixing, the properties of the fresh SCC mixes were evaluated by the slump flow and V-funnel tests [26]. Visual inspections were made during the slump flow test to check any noticeable segregation. Generally, a slump flow value of 600–800 mm is often targeted for normal SCC mixes. Specimens for compressive strength and flexural strength were prepared by simply pouring the fresh concrete into standard cube and beam moulds without vibration. The specimens were demoulded after 24 hours and then placed in a water tank for standard water curing. The hardened SCC specimens were tested for compressive strength at 7 and 28 days. The physical properties of coarse and fine aggregate are given in Table 1, while the physical properties of CA and BD are given in Table 2.

Different SCC mixes tested for filling ability and passing ability. After mixing, the properties of the fresh SCC mixes were evaluated by the slump flow and V-funnel tests . Visual inspections were made during the slump flow test to check any noticeable segregation. Generally, a slump flow value of 600–800 mm is often targeted for normal SCC mixes. Specimens for compressive strength and flexural strength were prepared by simply pouring the fresh concrete into standard cube and beam moulds without vibration. The specimens were demoulded after 24 hours and then

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placed in a water tank for standard water curing. The hardened SCC specimens were tested for compressive strength and flexural strength at 7, 28 and 56 days

Table 1: Physical Properties of Coarse and Fine Aggregates

Physical property Coarse aggregate Fine aggregate Specific gravity 2.68 2.65 Fineness modulus 6.85 2.34 Bulk density(kg/m3) 1535 1640 Water absorption 1.22 1.55

Table 2: Physical Properties of Brick Dust & Coal Ash

Properties Coal Ash

Specific Gravity Of Coal Ash (G) 2.10

Maximum Dry Density (gm/cc) 1.101

Constant Head Permeability (K) 1.24 x 10-3 cm/sec

Optimum Moisture Content (%) 27.4 %

Angle Of Internal Friction(φ) 330

Compression Index(Cc) 1.41

Coefficient Of Uniformity(Cu) 8.56

Properties Brick Dust Moisture Content(%) 4.2 Specific Gravity 2.6 Fineness Modulus 2.11 Bulk Density Loose(kg/m3) 1181.8 Bulk Density Compacted (kg/m3) 1370.8

Table 3: Test Results of Self Compaction

Mix Spread (mm) Slump flow time (sec.)

V Funnel U flow

EFNARC Range 650-800 2-5 6-12 0.8-1.0 SM 500 3.1 8 0.82 SM1 530 2.6 8.1 0.85 SM2 540 2.4 9 0.88 SM3 565 2.8 9.2 0.9 SM4 575 3.7 10.2 0.96

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Table 4: Test Results at different replacement Levels of fine aggregate with Brick Dust

Table 5: Test Results at different replacement Levels of fine aggregate with Coal Ash

%age Replacement with Brick Dust

Cube Compressive Strength (MPa) 7 day 28 day

0 34.5 47.9 25 33.9 46.7 50 27.4 41.4 75 16.2 23.5 100 13 18.9

Table 6: Test Results at different replacement Levels of fine aggregate with Brick Dust & Coal Ash

%age Replacement with Brick Dust & Coal Ash

Compressive Strength (MPa) 7 day 28 day

0 34.5 43.9 12.5BD+12.5CA 31.8 42.4 25.0BD+25.0CA 27.6 38.3 37.5BD+37.5CA 22.3 36.0 50.0BD+50.0CA 13.9 23.3

CONCLUSIONS

All concretes mixes using brick dust and coal ash fulfilled the performance criteria for fresh and hardened SCC. One of the main objectives of the experimental work was to study the viability of using brick dust and coal ash as a partial substitute of fine aggregate and the investigations indicate that such local waste material can produce good self-compacting concrete. The replacement of fine aggregate with BD and CA was found to be beneficial to fresh self-compacting concrete. 25% replacement of fine aggregate with BD or CA has given good results without any significant decrease in compressive strength. For 50% and 75% replacement there is a significant decrease in compressive strength but that decrease in strength, but that decrease is compensated by saving in natural resource i.e. fine aggregate. Overall it can be concluded that waste material like BD and CA can be easily used as replacement for fine aggregate for medium strength SCC.

Reference

%age Replacement with brick dust

Cube Compressive Strength (MPa) 7 day 28 day

0 34.5 48.9 25 34 47.5 50 28 42.6 75 24.8 37.7 100 17.5 24.8

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Chai,H.W (1998)”Design and testing of self compacting concrete “PhD Thesis Department of Civil and Environmental Engineering ,University College London.

EFNARC: Specification and Guidelines for Self-Compacting Concrete. Farnham, February 2002. Gagne, R., Pigeon, M., and Aitcin, P. C. (1989). “Deicer salt scaling resistance of high performance

concrete Paul Klieger Symposium on Performance of Concrete, SP-122, ACI. Hayakawa, M., Matsuoka, Y., and Shindoh, T. (1993) “Development & application of super workable

con crete.” RILEM International Workshop on Concretes: Workability and Mixing. Library of JSCE, 25, pp. 107-120.

IS: 456-2000(2000)”Code of practice plain and reinforced concrete” Bureau of Indian Standards, New Delhi.

IS: 516-1959(reaffirmed 1999) “Methods of tests of concrete” Bureau of Indian Standards, New Delhi IS: 383-1970(reaffirmed1997):”Specifications of coarse and fine aggregates from natural sources of

concrete “Bureau of Indian Standards, New Delhi. Neville, A. M, “Properties of concrete”, Longman Publishers,pp-300 Okamura, H .and Ouchi, M., (2003).“Self-compacting concrete”, Journal of Advance Concrete

Technology, Vol. 1, No. 1, April, pp. 5-15. Okamura, H. and Ozawa, K., (1995). “Mix design for self-compacting concrete”, Concrete Ramchandran, V. S and Malhotra (1981)” Superplasticizer in concrete admixtures handbook”park

ridge,N.J.Noyes Publication,pp211-268 Uno, Y. (1999). “State-of-the art report on concrete products made of SCC,” Proceedings of the

International Workshop on Self-Compacting Concrete, 262- 291.

391

DEVELOPMENT OF SELF COMPACTING CONCRETE USING RICE HUSK ASH AS A

SUPPLEMENTARY CEMENTING MATERIAL

Kanwarjeet Singh Bedi, Gurbir Kaur Jawanda and Rajinderpal Kaur Department of Civil Engineering, GNDEC, Ludhiana, Punjab, India

Abstract: Self compacting concrete (SCC) is an advanced form of conventional concrete, in which the use of vibrator for compaction is has been completely removed. This property of self compacting concrete has made its use more attractive all over the world. But its initial higher supply cost over conventional concrete, has hindered its application to general construction. Therefore, for producing low cost SCC, it is prudent to look at the alternates to help reducing the SSC cost. The present study explores the economic viability of Rice Husk Ash (RHA) as supplementary cementing material in self compacting concrete. Tests were carried out on all mixtures to obtain the properties of fresh concrete in terms of viscosity and stability. Respective specimens were prepared by replacing 10 - 40% cement with RHA. Mechanical properties like compressive strength and flexural strength was determined at 7, 28 and 56 days of curing. The content of the cementitious materials, aggregate and admixtures were maintained constant (450 kg/m3), while varying the water/cement ratios to obtain desired workability. The obtained results confirm the viability of adding RHA to the concrete. RHA can be conveniently used as a pozzolanic material to improve the microstructure of the interfacial transition zone (ITZ) between the cement paste and the aggregate in SCC. In the fresh state of concrete, the different mixes of concrete have slump flow in the range of 650 mm to 775 mm. All the mixes were found to satisfy the requirements suggested by European federation of national trade associations representing producers and applicators of specialist building products (EFNARC) guide for making self compacting concrete. The compressive strengths developed by the self compacting concrete mixes with RHA at 28 and 56 days were comparable to the control concrete.

Keywords: Self compacting concrete, rice husk ash, supplementary cementitious material, pozzolanic activity, rheology

INTRODUCTION

Self compacting concrete (SCC) requires excellent filling ability, good passing ability and adequate segregation resistance and is produced by exploiting the benefits of high-range water reducer (HRWR) and supplementary cementitious material (SCM). A HRWR contributes to achieve excellent filling ability and passing ability. of the sugar-bearing juice from sugarcane as SCM is very limited due to lack of awareness and high cost associated with its production. The objectives of this work were to synthesize and characterize the bagasse ash and rice husk ash obtained under factory processing conditions and which are agricultural wastes generated in the rice-milling industry. The present study has attempted to develop cost effective SCC utilising RHA and SBA as a SCM.. The silica contents of bagasse and its ash are varied depending on the type of soil and harvesting .India is the second largest producer of rice in the world with yearly

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RHA potential of about 4.5 million metric tons. Worldwide, about 120 million metric tons of rice husks are available annually for disposal. Hence, RHA and SBA not only improve concrete properties and durability, but also provide substantial economic and environmental benefits. The bagasse ash is the main by-product of the sugar-alcohol industry, which presents a period of great growth. Although SCC offers many technical and overall economical benefits, the higher supplied cost of SCC over normal concrete has limited its applications. The usage of RHA can minimise the environmental burden resolving vast waste disposal problems caused by rice milling industries.

It is known that bagasse ash is an alternative source of energy with high silica content. In addition, SCMs are incorporated in SCC mostly to enhance the strength and durability of concrete. In India and other countries, several well-known SCMs such as fly ash, ground granulated blast-furnace slag, metakaolin and silica fume have been used to produce SCC. In comparison, the use of rice husk ash (RHA) in SCC as SCM is very limited due to lack of awareness and high cost associated with its production. The present study has attempted to develop cost effective SCC utilising RHA as a SCM.

RICE HUSK ASH USAGE IN INDIA RHA is obtained by controlled burning of rice husks, which are agricultural wastes generated in the rice-milling industry. It has been found that RHA provides dramatic improvements in hardened properties and durability of concrete. India has a major agribusiness sector which has achieved remarkable successes over the last three and a half decades. Agricultural waste or residue is made up of organic compounds from organic sources such as rice straw, oil palm empty fruit bunch, sugar cane bagasse, coconut shell, and others. Rice husk from paddy (Oryza sativa) is one example of alternative material that has a great potential. Rice husk a major by-product of the rice milling industry, is one of the most commonly available lignocellulosic materials that can be converted to different types of fuels and chemical feedstocks through a variety of thermochemical conversion processes. Rice husk is an agricultural residue abundantly available in rice producing countries.The husk surrounds the paddy grain. During milling of paddy about 78 % of weight is received as rice, broken rice and bran. Rest 22 % of the weight of paddy is received as husk. This husk is used as fuel in the rice mills to generate steam for the parboiling process. This husk contains about 75 % organic volatile matter and the balance 25 % of the weight of this husk is converted into ash during the firing process, is known as rice husk ash. This RHA in turn contains around 85 % - 90 % amorphous silica.The moisture content ranged from 8·68 to 10·44%, and the bulk density ranged from 86 to 114 kg/ m3. Similar effects might be observed when RHA is used in SCC. SCMs are also essential for high strength and high durability of SCC. Moreover, the expense of some SCMs such as silica fume and high reactivity metakaolin increases the overall material cost of SCC. Therefore, the use of less-expensive RHA is more desirable to decrease the overall production cost of SCC. Although SCC offers many technical and overall economical benefits, the higher supplied cost of SCC over normal concrete has limited its applications. The usage of RHA can minimise the environmental burden resolving vast waste disposal problems caused by rice milling industries. The yearly production of rice in the world is about 560 million metric tons. . Rice husk constitutes approximately one fifth of the dried rice . India is the second largest producer of rice in the world with yearly RHA potential of about 4.5 million metric tons. Worldwide, about 120 million metric tons of rice husks are available annually for disposal. This is causing a huge environmental load for rice-producing countries, which can be reduced dramatically if a large part RHA is used in concrete production. Thus, the incorporation of RHA in SCC is a novel solution to the environmental problem caused by rice husks. Also, the use of RHA can lower the demand for cement in construction industry and thus reduces the cost of cement

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production and lessens the environmental pollution caused by cement factories. Hence, RHA not only improves concrete properties and durability, but also provides substantial economic and environmental benefits

MATERIALS Self-consolidating concrete is designed to meet specific applications requiring high deformability, high flow ability and high passing ability. The rheological properties and robustness of SCC vary in a wide range. It is more susceptible to changes than ordinary concrete because of a combination of detailed requirements, more complex mix design and inherent low yield stress and viscosity. Variations in properties (and robustness) are attributed therefore to the specific effects of the ingredients on the rheological properties of the mixture, effects of the physical properties (i.e. size and specific density) of the aggregate and the mixing history. Aggregates, cement, water and HRWR are the principal materials of SCC where as SCM, VMA and other chemicals can be used as the optional materials. The brief illustration of component materials of SCC is given below.

• Coarse Aggregate

Coarse aggregates used for the study was natural coarse aggregates (angular type of 20 and 12.5mm of size) .They were then washed to remove dust and were dried to surface dry condition.The nominal maximum size for SCC can be 20 or 25 mm. However, the smaller size is preferable to produce higher strength and to reduce segregation in fresh SCC. Round aggregates are better than angular aggregates for flowing ability of SCC. The well-graded coarse aggregates contribute to produce the optimum mixture with least particle interference and thus enhance the flowing ability and reduce the tendency of segregation in fresh concrete. They also improve the hardened properties and durability of concrete due to dense particle packing.

• Fine aggregate

Locally available sand was used for this study. The sand was tested as per (IS 383-1970) and the properties obtained .A fineness modulus in the range of 2.5 to 3.2 is generally recommended for SCC. As per our results the Specific gravity was 2.65 ,Water absorption was 1.1% and Fineness modulus was 2.2.Fine aggregates increase the flowing ability and segregation resistance when used at a suitable amount. In addition, they modify the strength of concrete when used in varying proportion with cement and coarse aggregates.. Furthermore, the well-graded fine aggregates contribute to improve the packing density and thus the hardened properties and durability of concrete. A fineness modulus in the range of 2.5 to 3.2 is generally recommended for SCC. Physical properties of coarse and fine aggregate used in experimental work are given in table 2.

• Cement

Ordinary portland cement is most widely used to produce various types of concrete. The cement used for SCC should have sound flow and setting properties. For present work ordinary portland cement of 43 grade from single lot was used in this investigation with specific gravity 3.10. It was fresh and without lumps. All tests on cement were conducted, as per procedure laid down in IS 8112:1989.The cement should possess carefully controlled fineness, and should

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produce low or moderate heat of hydration to control the volume changes in concrete. The properties of cement used in experimental work are given in table 1.

• Viscosity modifying admixture

VMA improves the viscosity and cohesion of fresh concrete and thus reduces the bleeding, surface settlement and aggregate sedimentation resulting in a more stable and uniform mix. The viscosity modifying admixture used in this study is “STRUCTURO 100”(Source -FORSOC Chemicals (India). Structuro 100 is used in self compacting concrete, pumped concrete, concrete requiring long workability retention, high performance concrete. The mechanism of viscosity enhancement depends on the type of VMA. Generally they work through the mechanisms of adsorption, association and intertwining.

• Supplementary cementing materials

Supplementary cementing materials are finely divided materials, which contribute to the properties of the hardened concrete through hydraulic or pozzolanic activity. RHA is a good super-pozzolans. Silpozz can be used in a big way to make special concrete mixes. There is a growing demand for fine amorphous silica in the production of special cement and concrete mixes, high performance concrete, high strength, low permeability concrete, for use in bridges, marine environments, nuclear power plants etc. This market is currently filled by silica fume or micro silica, being imported from Norway, China and also from Burma. Due to limited supply of silica fumes in India and the demand being high the price of silica fume has risen to as much as US$ 500 / ton in India They are greatly beneficial for concrete properties and durability due to their effective physical and chemical effects on material packing and microstructures. Silica fume, fly ash, ground granulated blast-furnace slag, RHA and metakaolin can be used as SCMs. The ASTM has specified the physical and chemical requirements for natural and most artificial SCMs. These requirements mainly provide the limits for fineness, expansion or contraction, pozzolanic activity, uniformity, and reactivity. However, currently there is no Indian Standard (IS) or ASTM physical or chemical requirements for RHA.

• Rice husk ash

Rice husk ash is produced by incinerating the husks of rice paddy. Rice husk is a by-product of rice milling industry. Controlled incineration of rice husks between 5000C and 8000C produces non-crystalline amorphous RHA which is whitish or gray in colour. The particles of RHA occur in cellular structure with a very high surface fineness and 90% to 95% amorphous silica. Due to high silica content, RHA possesses excellent pozzolanic activity. The physical properties of RHA largely depend on burning conditions. The controlled burning at about 5000C to 8000C results in non-crystalline or amorphous silica, which shows very high pozzolanic activity . Unlike silica fume, the RHA particles are porous and possess a honeycomb microstructure. The specific surface area of RHA is as high as 2000 m2/kg. Properties of RHA used in experimental work is given in table 3.

STABILITY OF SELF-CONSOLIDATING CONCRETE

The stability of SCC refers to its ability to resist phase separation such as bleeding and segregation of the paste from the aggregates or the settlement of coarse aggregates during and after placement. Generally, two forms of stability are a concern for the fresh SCC; static and dynamic stabilities.

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Both static and dynamic stabilities must be ensured in SCC to obtain uniform distribution of the constituent materials particularly coarse aggregates, throughout the concrete component .

• Role of rice husk ash

The stability of SCC is mainly controlled by its mixture variables. The properties and proportions of cementing materials have significant effect on both static and dynamic stability . If SCC suffers from instability problem, it can be eliminated by increasing the amount of SCM [25]. However, it depends on some physical properties such as particle shape and size, specific surface area, and relative density of SCM. These properties influence the yield stress, viscosity and density of the cement paste matrix that affect the stability of SCC [24]. Since the yield stress, plastic viscosity and density of the paste matrix are changed in the presence of RHA, both static and dynamic stability of SCC can be influenced by adding RHA.

PRESENT WORK The present work deals with the development of SCC incorporating RHA as a supplementary cementing material. Various SCC mixes were produced by replacement of cement with RHA in varying percentage of 0,10 20, 30 and 40 with the addition of VMA and HRWR in the mix.

Table 1: Physical Properties of cement

Physical property Test results of Cement(OPC 43 grade)

Colour Grey(light)

Fineness(m2/kg) 310

Specific gravity 3.15

Initial setting 90

Final setting 180

3 day compressive strength (MPa) 25.3

7 day compressive strength (MPa) 37.6

28 day compressive strength(MPa) 43.2

. RESULTS AND DISCUSSION

SCCs were tested for filling ability and passing ability. After mixing, the properties of the fresh SCC mixes were evaluated by the slump flow and V-funnel tests. Visual inspections were made during the slump flow test to check any noticeable segregation. Generally, a slump flow value of 600–800 mm is often targeted for normal SCC mixes. Specimens for compressive strength and flexural strength were prepared by simply pouring the fresh concrete into standard cube and beam moulds without vibration. The specimens were demoulded after 24 hours and then placed in a

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water tank for standard water curing. The hardened SCC specimens were tested for compressive strength and flexural strength at 7, 28 and 56 days

Table 2: Physical properties of coarse and fine aggregates Physical property Coarse aggregate Fine aggregate Specific gravity 2.68 2.65 Fineness modulus 6.85 2.34 Bulk density(kg/m3) 1535 1640 Water absorption 1.22 1.55

Table 3: Chemical properties of rice husk ash

Constituent RHA(%by weight) Silica(Sio2) 94.23 Alumina(Al2O3) 2.7 Iron oxide(Fe2O) 0.25 Carbon 1.25 Magnesium oxide(MgO) 0.56 Calcium oxide(CaO) 1.58 Alkaline oxide(K2O) 0.43

• Tests on fresh concrete

Various test methods which are commonly used to measure the workability of SCC. The consistency of the concrete mix is assessed by the slump and the time needed to attain a slump of 500 mm (T50), using the Abrams cone. The final slump should range from 500 mm to 575 mm. The V-funnel test gives an indication of the viscosity and filling time of the mix. To assess the preservation of the workability, the Slump-flow test was also conducted at 15, 30, 45, 60, 90 and 120 minutes after preparation of the mixes. Table 4 shows mix proportions at various replacement levels of cement with RHA and Table 6 shows different self compactibility test results

Table 4: Mix Proportions (kg/m3)

Mix Cement

Coarse Agg.

Fine Agg.

Rice husk Ash

Water

HRWR

VMA

SM 450 900 800 0 135.0 3.4 1.28 SM1 405 900 800 45 153.0 3.4 1.28 SM2 360 900 800 90 166.5 3.4 1.28 SM3 315 900 800 135 180.0 3.4 1.28 SM4 270 900 800 180 197.3 3.4 1.28

Where, SM – 0% Cement replaced by rice husk ash SM1– 10% Cement replaced by rice husk ash SM2 – 20% Cement replaced by rice husk ash. SM3 – 30% Cement replaced by rice husk ash. SM4 – 40%Cement replaced by rice husk ash

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• Tests on hardened concrete

Cubes of size 150 mm and beams of size 100 x 100 x 600 mm of different mixes were casted by pouring concrete directly into the moulds and without any use of vibrator. Cubes and beams were demoulded after 24 hours and placed into curing tank. The specimens were tested for compressive and flexural strength on 7, 28 and 56 days respectively, the results of which are given in table.

Table 5: Test Results of Compressive Strength

Mix designation %replacement Curing 7 days(MPa)

Curing 28 days(MPa)

Curing 56 days(MPa)

SM 0 6.4 7 11.1 SM1 10 7.8 9.3 12.9 SM2 20 6 7.9 10.2 SM3 30 5.1 6.3 7.2 SM4 40 7.4 5.8 6.7

For all the SCC mixes 28 and 56 day hardened properties indicate considerable improvement at later stage. This was due to greater hydration of cement and increased pozzolanic activity due to the addition of RHA.

From 10-20% replacement, the hardened properties of the SCCs were improved with increase in RHA content. Between 10-20% there was slight decrease in compressive and flexural strength, with which may be due to the increase in water binder (W/B) ratio. Between 20-30% there was progressive decrease in compressive as well as flexural strength.

CONCLUSIONS

The hardened properties of the SCC specimens improved gradually with the increased RHA content. All concretes mixes using RHA fulfilled the performance criteria for fresh and hardened SCC. Excellent hardened properties were achieved for the concretes with 10 to 15% RHA which can be considered as the optimum content for high compressive strength. However, RHA content greater than 15% caused mixing and handling difficulties due to excessive cohesiveness or stickiness, particularly at lower W/B ratios. The hardened properties of the SCCs were improved at later ages such as 28 and 56 days due to greater hydration of cement and enhanced pozzolanic activity of RHA. The hardened properties of the SCCs were improved due to closed packing, resulting from greater hydration products in the presence of higher binder content. More than 15% replacement of cement with RHA gradually decreases the compressive strength of SCC mixes. Comparison of 10 and 30% replacement level indicates 0.4 times decrease in compressive strength which is relatively good keeping in mind 20% saving in cement and easy attainability of self compaction. In this study an effort has been made to evaluate the usefulness of RHA, an agro-industry waste, as a mineral admixture in producing cost effective SCC.

References

Mehta, P.K., and Folliard, K.J., “Rice husk ash – a unique supplementary cementing material: durability aspects”, Proceedings of the Second ACI International Symposium on Advances in Concrete Technology, ACI SP-154, V.M. Malhotra, ed., American Concrete Institute, Farmington Hills, Michigan, USA, 1995, pp.531-541.

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Vegas, P. “Rice production and marketing”, Sage V Foods, LLC, Los Angeles, California, USA, 2004. Mehta, P.K., “Rice husk ash – a unique supplementary cementing material”, Proceedings of the CANMET/ACI International Symposium on Advances in Concrete Technology, V.M. Malhotra, ed., Athens, Greece, 1992, pp.407-430. Noguchi, T., Oh, S.G., and Tomosawa, F., “Rheological approach to passing ability between reinforcing bars of self-compacting concrete”, Proceedings of the First International RILEM Symposium on Self-compacting Concrete, Â. Skarendahl, and Ö. Petersson, ed., RILEM Publications, Bagneux, France, 1999, 12pp. Okamura, H., and Ozawa, K., “Mix design for self-compacting concrete”, Concrete Library of JSCE, No.25, 1995, pp.107-120. Xie, Y., Liu, B., Yin, J., and Zhou, S., “Optimum mix parameters of high-strength self-compacting concrete with ultrapulverized fly ash”, Cement and Concrete Research, Vol.32, No.3, 2002, pp.477-48. ACI 211.4R-93, “Guide for selecting proportions for high-strength concrete with portland cement and fly ash”, ACI Manual of Concrete Practice, Part 1, American Concrete Institute, Farmington Hills, Michigan, USA, 2004, 13pp. Taylor, M.R., Lydon, F.D., and Barr, B.I.G., “Mix proportions for high strength concrete”, Construction and Building Materials, Vol.10, No.6, 1996, pp.445-450. Shilstone, Sr., J.M., “Concrete mixture optimization”, Concrete International, Vol.12, No.6, 1990, pp.33-39. Neville, A.M. Properties of Concrete, Fourth and Final Edition, John Wiley & Sons, Inc., New York, USA, 1996, 844pp Tasi, C.T., Li, S., and Hwang, C.L., “The effect of aggregate gradation on engineering properties of high performance concrete”, Journal of ASTM International, Vol.3, No.3, 2006, pp.1-12. Su, J.K., Cho, S.W., Yang, C.C., and Huang, R., “Effect of sand ratio on the elastic modulus of self-compacting concrete”, Journal of Marine Science, Vol.10, No.1, 2002, pp.8-13. Hu, J., and Wang, K., “Effects of aggregate on flow properties of mortar”, Proceeding of the Mid-Continent Transportation Research Symposium, Ames, Iowa, Iowa State University, 2005, 8pp. Nawy, E.G., Fundamentals of High Strength High Performance Concrete, Longman Group Limited, London, UK, 1996. 340pp. Khayat, K.H., “Viscosity-enhancing admixtures for cement-based materials – an overview”, Cement and Concrete Composites, Vol.20, No.2-3, 1998, pp.171-188. Khatri, R.P., and Sirivivatnanon, “Effect of different supplementary cementitious materials on mechanical properties of high performance concrete”, Cement and Concrete Research, Vol.25, No.1, 1995, pp.209-220. Mehta, P.K., “Mineral Admixtures for Concrete – an Overview of Recent Developments”, Advances in Cement and Concrete: Proceedings of an Engineering Foundation Conference, M.W. Grutzeck, and S.L. Sarkar, eds., American Society of Civil Engineers, New York, USA, 1994, pp. 243-256. ASTM C 618, “Standard specification for coal fly ash and raw or calcined natural pozzolan for use as a mineral admixture in concrete”, Annual Book of ASTM Standards, Vol.04.02, American Society for Testing and Materials, Philadelphia, USA, 2004. ASTM C 989, “Standard specification for ground granulated blast-furnace slag for use in concrete and mortars”, Annual Book of ASTM Standards, Vol.04.02, American Society for Testing and Materials, Philadelphia, USA, 2004. ASTM C 1240, “Standard specification for use of silica fume as mineral admixture in hydraulic cement concrete, mortar and grout”, Annual Book of ASTM Standards, Vol.04.02, American Society for Testing and Materials, Philadelphia, USA, 2004. Mehta, P.K., and Monteiro, P.J.M., Concrete: Microstructure, Properties, and Materials; Second Edition, McGraw-Hill Companies, Inc., New York, USA, 1993. 548pp. Zhang, M.-H., and Malhotra, V.M., “High-performance concrete incorporating rice husk ash as a supplementary cementing material”, ACI Materials Journal, Vol.93, No.6, 1996, pp.629-636.

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Bui, V.K., Montgomery, D., Hinczak, I., and Turner, K., “Rapid testing method for segregation resistance of self-compacting concrete”, Cement and Concrete Research, Vol.32, No.9, 2002, pp.1489-1496. Saak, A.W., Jennings, H.M., and Shah, S.P., “New methodology for designing self-compacting concrete”, ACI Materials Journal, Vol.98, No.6, 2001, pp.363-371. Nagataki, S., and Fujiwara, H., “Self-compacting property of highly flowable concrete”, Proceedings of the Second CANMET/ACI International Symposium on Advances in Concrete Technology, SP-154, V.M. Malhotra, ed., American Concrete Institute, Farmington Hills, Michigan, USA, 1995, pp.301-314. EFNARC, Test methods—Annex D, Specifications and Guidelines for Self-Compacting Concrete, web site: http://www.efnarc.org, 2002, 21–24.

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SHEAR STRENGTH CHARACTERISTICS OF SELF COMPACTING CONCRETE USING

FLYASH AND SILICA FUME

Kanwarjeet Jeet Singh Bedi, Rajesh Kumar* and Harpreet Kaur Department of Civil Engg, GNDEC, Ludhiana

*Department of Civil Engg, PTU GZS Campus Bathinda

Abstract: The use of self-compacting concrete in major constructions has become obligatory, whose mechanical properties are still at a research phase. This work deals with the review of available data base and shear models to predict the shear strength of self -compacting concrete beams without web reinforcement. Experimental investigations have been carried out to study shear strength of self-compacting concrete beams having different shear span to depth ratios. Fly ash and silica fume was used as supplementary cementitious material for making self compacting concrete. Test results were compared with ACI Code Equation, Zsutty Equation andnIS:456-2000 Equation.

Key- Words: beams, Self-compacting concrete (SCC), longitudinal reinforcement ratio, shear failure, shear strength, shear span to depth ratio, a/d ratio.

INTRODUCTION Self-compacting concrete (SCC) is being used extensively in the construction industry all over the world. Self-compacting concrete (SCC) is a new generation of high performance concrete known for its excellent deformability and high resistance to segregation and bleeding. Lack of information regarding in situ properties and structural performance of SCC is one of the main barriers to its acceptance in the construction industry. There is some concern among researchers and designers that SCC may not be strong enough in shear because of some uncertainties in mechanisms resisting shear notably the aggregate interlock mechanism. Because of the presence of comparatively smaller amount of coarse aggregates in SCC, the fracture planes are relatively smooth as compared with normal concrete (NC) that may reduce the shear resistance of concrete by reducing the aggregate interlock between the fracture surfaces. The paper investigates the shear resistance of SCC on the results of an experimental investigation on 9 flexurally reinforced beams without shear reinforcements. The recommendations of this paper can be of special interest to designers considering the use of SCC in structural applications. To estimate the shear resistance of beams, standard codes and researchers all over world, have specified different formulae considering different parameters into consideration. The parameters considered are varying for different codes and researchers leading to disagreement between researchers, making it difficult to choose an appropriate model or code for predicting shear resistance of reinforced concrete. Therefore an extensive research work on shear behavior of normal and self-compacting concrete is being carried out all over the world. Estimation of shear resistance of high strength concretes is still controversial therefore it’s a thrust area for research. Predictive parameters influencing Shear Strength: The shear transfer mechanisms help identify predictive parameters that may affect the

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shear strength of a RC beam, such as concrete compressive strength, beam depth, shear span-to-depth ratio, amount of longitudinal reinforcement and axial forces. The shear strength of a beam increases as the concrete material strength increases. The concrete tensile strength is known to have a great influence on the shear strength, but the concrete compressive strength is used instead in most shear strength formulas. This is because tensile tests are more difficult to conduct and usually show greater scatter than compression tests

SIGNIFICANCE OF RESEARCH

The priority of this study was given to solve the mystery of shear strength characteristics of beams cast with high grade of self-compacting concrete. For shear strength evaluation of self-compacting concrete, beams of varying length with different values of effective-span to depth ratio is casted with constant depth. Therefore, proposed investigation was based on the influence of beams of varying size that is shear span to depth on the shear strength of concrete beams without shear reinforcement, to ascertain experimentally whether the following hypothesis holds good or not.

OBJECTIVE

• To evaluate the shear strength of high strength SCC beams without shear reinforcement. • To study the effect of shear span to depth ratio on the shear strength of the self-

compacting concrete beams. • To compare the provisions and procedures given in IS 456-2000 for the shear design.

EXPERIMENTAL PROGRAM

In this work, beam specimens were made, in order to be tested for shear strength after 28 days of standard curing. Self-compacting concrete beam specimens were tested for shear strength, for each of the effective span to depth ratios. Tests were carried out on 9 beams, simply supported under two points loading. All the beams had constant cross section of 150mm x 300mm illustrated in Figure 1. The length of beam was worked out to be 1.7m, 2.3m and 2.9m for corresponding a/d ratio = 1.5, 2.5 and 3.5 respectively. All the three series of beams were provided with steel bars as longitudinal reinforcement to avoid any possible failure by flexure and the grade of concrete was taken M80. Also, for self-compacting concrete, slump flow, U-type, V-Funnel and L-box tests were carried out in order to evaluate the filling ability and the passing ability of self-compacting concrete.

Beam-1, b=150mm, D=300mm, Span= 1700mm

Beam-2, b=150mm, D=300mm, Span= 2200mm

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Beam-3, b=150mm, D=300mm, Span= 2700mm

Fig 1: Proposed beam sizes and their loading arrangements

MATERIALS USED

• Cement

Ordinary Portland cement of 43 grade from single lot was used in this investigation. It was fresh and without lumps. All tests on cement were conducted, as per procedure laid down in code IS: 8112-1989. The properties of cement were given in Table 1.

Table 1- Physical properties of OPC cement

Sr. No.

Characteristics Specified values as per IS:8112-1989

Results observed

1. Standard Consistency (in %) - 37 2. Specific gravity 3.15 3.15 3. Initial Setting Time (in mins) >30mins 65 4. Final Setting Time (in mins) <600mins

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5. Fineness (Blaine’s apparatus) (in %) <10 4.8

• Fine aggregate

IS 383–1970 defines the fine aggregate as the one, which passing 4.75 mm IS sieve. The fine aggregate is often termed as a sand size aggregate. Locally available sand was used for this study. The sand was tested as per (IS 383-1970) and the properties obtained are given in table. The sand conforms to grading Zone – II as per IS: 383 – 1970

Table 2 - Physical properties of Fine Aggregates

Sr. No. Characteristics Results Obtained

1. Specific gravity 2.65 2. Water absorption (in %) 1.1% 3. Fineness modulus( in m2/g) 2.2 4. Grading zone Zone-II (IS:383-1970)

• Coarse Aggregates

The coarse aggregate is defined, as that retained on 4.75 mm IS sieve. To increase the density of the resulting concrete mix, the coarse aggregate is frequently used in two or more sizes. Two

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types of aggregate with different sizes have been used in the present study. The details of the same are as below:

CA – I Aggregate passing 20 mm sieve and retained on 12 mm sieve. CA – II Aggregate passing 10 mm sieve and retained on 6 mm sieve.

The properties of these aggregates have been listed in Table 3. The percentage contributions of aggregates have been taken as 50% CA – I and 50% CA – II for proportioning of the concrete mix. The coarse aggregates used were washed to remove dust and dirt and were dried to surface dry condition.

Table 3 - Physical Properties of Coarse Aggregates

Sr. No. Characteristics Results obtained

1. Type Crushed 2. Shape Angular 3. Specific gravity 2.65% 4. Color Grey 5. Water absorption 1.0% 6. Fineness modulus 7.87

• Fly ash

Investigations were made on fly ash procured from Ultra Tech RMC Plant. It was tested for chemical and physical properties per ASTM C 311.The chemical and physical properties of the fly ash used in this investigation are listed in Table 4.

Table 4- Physical Properties of Fly Ash

Sr. No. Characteristics ASTM C 618 Specified values

Results Obtained

1. Fineness Specific Surface (cm2/gm)

3200(min) 3258

2. Residue on 45 micron (wet sieving)

34(max) 30.17

3. Lime Reactivity (kg/cm2) 45 (min) 51.03 4. Compressive strength

(kg/cm2), 28 days

Not less than 80% of strength of corresponding plain cement Mortar cubes

85.99

5. Dry shrinkage (in %) 0.15(max) 0.04 6. Soundness expansion by

auto clave, % 0.8(max) 0.03

• Silica Fume

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Silica fume, also known as microsilica or condensed silica fume is a pozzolanic admixture. When used in concrete it will fill the void space between cement particles resulting in a more impermeable concrete. The silica fume used in this study is provided by Elkem India Pvt. Ltd. (Microsilica Grade 940-D). Elkem Microsilica Grade 940 which we had used was dry form of silica fume. The properties of microsilica according to ISO 9001 are given in the table 5.

Table 5- Properties of Microsilica

Sr. No. Characteristics Specified values 1. Specific Gravity 2.10 to 2.55 2. Color Pale grey to dark grey 3. H2O

(Moisture content when packed in %) <1 to 0

4. Specific Surface Area About2000m2/kg(approximately 10 times more than PC)

5. Particle size Mostly fine spheres with a mean diameter of 0.1 micron

6. Loss on Ignition (in %)

<3 to 0

7. Retained on 45 micron sieve (Tested on undensified in %)

<1 to 5

8. Bulk Density- Undensified (when packed in kg/m3)

200-350

9. Bulk Density- Densified (when packed in kg/m3)

500-700

• Viscosity Modifying Agent

The viscosity modifying admixture used in this study is “STRUCTURO 100” (Source -FORSOC Chemicals (India). Structuro 100 is used in self-compacting concrete, pumped concrete, concrete requiring long workability retention, high performance concrete. The advantages of VMA are listed below:

1. Increased early and ultimate compressive strength 2. Increased flexural strength 3. Higher E modulus 4. Improved adhesion to reinforcing and prestressing steel 5. Better resistance to carbonation 6. Lower permeability 7. Reduced shrinkage and creep 8. Increased durability

• Super-plasticizer

GLENIUM B233 is an admixture of a new generation based on modified poly-carboxylic ether. The product has been primarily developed for applications in high performance concrete where the highest durability and performance is required. GLENIUM B233 is free of chloride & low alkali. It is compatible with all types of cements. The properties of GLENIUM B233 are given in Table 6.

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Table 6- Typical Properties of GLENIUM B233

Sr. No. Characteristics Results Obtained 1. Aspect Light brown liquid 2. Relative Density 1.09 ± 0.01 at 25°C 3. pH >6 4. Chloride ion content < 0.2%

• Steel Reinforcing Bars

The steel reinforcing bars used were 8mm, 10mm and 12mm diameter high yield strength deformed bars of brand TATA Tiscon of grade Fe415. Various tests had done on these bars. The values obtained by conducting different tests are given in the table 7.

Table7- Experimental results of Steel

Sr. No. Characteristics Permissible values as per IS-800-1984

Results obtained

1. Ultimate Stress (in N/mm2)

>485 625

2. Proof Stress (in N/mm2)

>415 482

3. Elongation (in %)

>14 18.5

• Water

As per (IS 456-2000) portable water is considered for satisfactory mixing and curing of concrete. The water should be clean and free from harmful impurities such as oil, alkali, acid etc. In general the water is fit for drinking is used for making concrete.

MIX PROPORTION

The mix proportion for M80 of SCC was obtained from the trial mix results of EFNARC Guidelines. This mix proportion for Self Compacting concrete is summarized in the Table 8.

Table 8- Mix Proportion of M80

Mix Name

Cement

Fly Ash Silica Fume

Fine Aggregate

Coarse Aggregate Admixture (% of cement)

Water/ Cement Ratio

Greater than 10mm

Lesser than 10mm

SCC-1

1 0.145 0.0727 1.25 0.78 0.78 2.85% 0.30

• Preparation of testing specimens

406

Beam sized moulds of constant depth 300mm and width of 150mm with varying value shear span-to-depth ratio were used in order to determine shear strength of beams. Cube moulds of size 150x150mm and cylindrical moulds of size 150 mm×300 mm were used to prepare the concrete specimens for the determinations of compressive strength, split tensile strength of self-compacting concrete. All the moulds were cleaned and oiled properly. Concrete beams, cubes and cylinders were tested for the determinations of shear strength, compressive strength, split tensile strength and flexural strength of self-compacting concrete as per EFNARC Guidelines and Indian Standard Specifications IS: 516-1959, respectively.

• Batching, Mixing and Casting of specimens

A careful procedure was adopted in the batching, mixing and casting operations. The specimens were remained in the steel mould for the first 24 hours and after that these were demoulded with care so that no edges were broken and were placed for curing. All the details of testing specimens are given in a Table 9.

Table 9 - Schedule of beams

Sr. No.

Specimen Designation

Shear span-

to-depth Ratio (a/d)

Depth of beam(mm) Pt= 100Ast/ bd (%)

Number of Longitudina

l bars provided

Length of beam specimen

Overall Depth

(D) (mm)

Effective Depth (d)

(mm)

c/c support

distance, (mm)

Actual length

provided, L

(mm)

1 1SC80S5 1.5 300 265 0.5 2#12mm 1396 1650

2 2SC80S5 2.5 300 265 0.5 2#12mm 1926 2200

3 3SC80S5 3.5 300 265 0.5 2#12mm 2456 2700

DIFFERENT MODELS TO PREDICT SHEAR CAPACITY

• ACI code Equation. • Zsutty Equation • IS 456-2000 Code

• ACI Code Equation

According to ACI Building Code 318, the shear strength of concrete members without

transverse reinforcement subjected to shear and flexure is given by following equation.

Vc = . 16fc′ + 17 Vu d

Mu bw d(N) for a

d ≥ 2.5 (1)

407

Vc = 3.5 − 2.5MuVu d

× [Eq1] for ad

≤ 2.5 (1)a both shorter and long beams as it takes into account size effect and longitudinal steel effect.

• Zsutty Equation

Zsutty (1968) has formulated the following equation for shear strength of concrete members.

Vc = 2.2 fc′ p d

a bw d(N) for a

d ≥ 2.5 (2)

Vc = 2.5 da × [Eq 2] for a

d ≤ 2.5 (2a)

• IS 456-2000 Code Equation

The magnitude of the design shear strength τc depends on the various factors that are related

to the grade of concrete (fck) and the percentage tension steel pt = 100Ast/bd. The value of τc given

in the code (table 19) are based on the following empirical formula.

𝑽𝑽𝒄𝒄 = 𝟎𝟎.𝟖𝟖𝟖𝟖(𝟎𝟎.𝟖𝟖𝒇𝒇𝒄𝒄𝒄𝒄)𝟏𝟏+𝟖𝟖𝜷𝜷−𝟏𝟏𝟔𝟔𝜷𝜷

𝒃𝒃𝒘𝒘𝒅𝒅 (3) where, 𝜷𝜷 = 𝟎𝟎.𝟖𝟖𝒇𝒇𝒄𝒄𝒄𝒄

𝟔𝟔.𝟖𝟖𝟖𝟖𝒑𝒑𝒕𝒕 (3a)

or unity, whichever is greater f’c= Compressive strength of concrete at 28 days in MPa, bw= Width of cross section in mm, d= depth of Effective cross section in mm, Mu = Factored moment at Cross section, Vu= Factored shear force at Cross section, ρ – Longitudinal Reinforcement Ratio.

RESULTS

The test was conducted according to IS 516-1959. Specimens were taken out from curing tank at the age of 28 days and tested immediately after removal from water.

The beam specimens were tested for evaluating ultimate shear load. The specimens were tested as simply supported beams under two-point loading condition (Figure 2). The test setup included the use of a hydraulic jack that applied load gradually on the mid-span of beam specimens until shear failure occurs. The results of various tests were comprised in table 10 as follows.

408

b = 150 mm for all beams, D = 300mm, d = 265mm, a/d = 1.5, 2.5 and 3.5, pt = Ast/bd = 0.5%, 1%

and 2%

Fig 2: Test set-up configuration

Table 10:- Results of various Test

Comparison of the experimental results with predicted values of failure load using different models which were ACI code (Eq-1), Zsutty Equation (Eq- 2) and IS 456-2000 Code equation (Eq 3) at different values of a/d ratios were done. The results are tabulated in Table 11 and comparison was illustrated in Figure 3.

Sr. No.

Specimen Designation

Percentage of longitudinal

reinforcement pt, (%)

Shear span-to-

depth Ratio (a/d)

Compressive strength (in

Mpa) 28days

Ultimate Shear Load,

Vexp (kN)

Ultimate Shear Stress,

vus=Vu/bd (MPa)

1 1SC80S5 0.5 1.5 84.11 104.04 2.617

2 2SC80S5 0.5 2.5 83.63 80.35 2.013

3 3SC80S5 0.5 3.5 78.32 72.92 1.834

409

Table 11: Predicted and Experimental values of Failure Load

Fig 3: Graphical Representation of Comparison between Predicted Shear load and Experimental Results at

0.5% Percentage of Longitudinal Reinforcement.

CONCLUSIONS

The self-compacting concrete beams of M80 grade and with 0.5% longitudinal reinforcement were tested for ultimate shear strength with the varying values of shear span to depth ratio 1.5, 2.5 and 3.5. The width and depth of the beams were kept constant so as to check the failures occurring in beam which are mainly influenced by the varying value of shear span to depth ratio. Following are the conclusions drawn from the preset study.

1. The ultimate shear strengths of the SCC beams were found to be significantly dependent on the shear span-to-depth ratio (a/d) of beams. Shear strength of SCC beams decreases with increase in a/d ratio. With 0.5% longitudinal reinforcement the reduction in ultimate shear strength was 22.8%, 9.2% and 30.0% for change in a/d ratios from 1.5 to 2.5, 2.5 to 3.5 and 1.5 to 3.5 respectively.

Sr. No.

Specimen Designati

on

Percentage of longitudinal

reinforcement p, (%)

Shear span-to-depth

Ratio (a/d)

Experimental Failure

Load f, Vexp (kN)

Predicted Failure Load V predicted (kN)

ACI Code (Eq- 1)

Zsutty Equation (Eq- 2)

IS 456-2000 Code

(Eq- 3) 1 1SC80S5

0.5 1.5 104.04 39.21 106.3 23.85

2 2SC80S5 0.5 2.5 80.35 33.62 53.74 23.85 3 3SC80S5 0.5 3.5 72.92 30.34 48.04 23.85

410

2. Experimental shear stress values were compared with allowable shear stress values given in table 19 of IS-456 2000. IS 456-2000 does not take into account the influence of a/d ratio on shear strength and gives a constant value for M40 grade concrete and above. The shear strength of SCC beams calculated according to table 19 of IS: 456-2000 underestimate the shear strength by 70% as compared to experimental results obtained at 1.5, 2.5 and 3.5 a/d ratios.

3. As compared to experimental values ACI-318 code underestimate the shear strength of SCC beams by 65% for shear span to depth ratio of 1.5, 2.5 and 3.5.

4. Zsutty equation based on shear span-to-depth ratio and longitudinal reinforcement ratio along with grade of concrete is found to be more conservative in predicting the shear strength. The predicted values of shear strength with this equation are within of 2% to 10% variation when compared to experimental results of SCC beams. This proposed model to predict the ultimate shear strength is simple and predicts the shear strength of SCC beams with a fair degree of accuracy.

References

ACI 445R-99, “Recent Approaches to Shear Design of Structural Concrete”, reported by Joint ACI-ASCE Committee 445, November 1999, American Concrete Institute.

ACI 318-08, “Building Code Requirements for Structural Concrete (ACI 318-08) and Commentary”, January 2008, American Concrete Institute.

ACI Committee 318, Building Code Requirements for Structural Concrete (ACI 31802) and Commentary (318R02).

ACI-ASCE Committee 426, “The Shear Strength of Reinforced Concrete Members”, ACI Journal Proceedings, July 1973, V. 70, pp. 471-473.

Bazant, Z. P., and Kim, J. K., “Size Effect in Shear Failure of Longitudinally Reinforced Beams”, ACI Journal, September 1984, V. 81, pp. 456-468

CSA Technical Committee on Reinforced Concrete Design, Design of Concrete Structures A23.394,Rexdale, Ontario, 1994

European CEBFIP Model Code. London: Thomas Telfair, Services, 1990 Ferguson. P.M.,”Some Implications of recent Diagonal Tension Tests”, Journal of ACI, 28(2), 1956,

pp.157172 Hassan, A. A. A., Hossain, K. M. A., Lachemi, M., “Behaviour of full-scale self- consolidating concrete

beams in shear”, Cement & Concrete Composites, Elsevier Limited, April 2008. Hassan, T. K., Seliem, H. M., Dwairi, H., Rizkalla, S. H., and Zia, P., “Shear Behavior of Large

Concrete Beams Reinforced with High-Strength Steel”, ACI Structural Journal, March-April 2008, V. 105, pp. 173-179

Imran A. Bukhari and Saeed Ahmed, “Evaluation of Shear Strength of High Strength Concrete Beams without Stirrups.” The Arabian Journal for Science and Engineering, Vol33, Number 2B, October 2008, pp.323335.

IS 456: 2000, “Plain and Reinforced Concrete— Code of Practice”, reprint including amendment no.1, January 2005, Bureau of Indian Standards.

Jin Kuen Kim and YonDong Park. “Prediction of Shear Strength of Reinforced Beams without Web Reinforcement.” ACI Materials Journal, V 93, No. 3, MayJun 1996. pp. 213221.

Kani, G. N. J., “A Rational Theory for the Function of Web Reinforcement”, ACI Journal, March 1969, V. 66, pp. 185-197

Kani, G. N. J., “Basic Facts Concerning Shear Failure”, ACI Journal, June 1966, V. 63, pp.675-692

411

Moody, K. G., Viest, I. M., Elstner, R. C., and Hognestad, E., “Shear Strength of Reinforced Concrete Beams. Part 1: Tests of Simple Beams”, ACI Journal. Dec.1954, V. 51, pp. 317-332

Sherwood E. G., Bentz, E. C., and Collins, M. P., “Effect of Aggregate Size on Beam-Shear Strength of Thick Slabs”, ACI Structural Journal, March-April 2007, V. 104, pp. 180-190

Zsutty, T. C., “Shear Strength Predictions for Separate Categories of Simple Beam Tests”, ACI Journal, Proceedings, 68(2) (1971), pp. 138–143. Piotr Paczkowski and Andrezej, Nowak, S., “Shear Resistance of Reinforced Beams without Web Reinforcement.” Architecture Civil Engineering Environment Journal No. 1/2008. pp 99112.

412

OPTIMUM DESIGN OF GEOSYNTHETIC REINFORCED SOIL FOUNDATION USING

GENETIC ALGORITHM

Siddharth Das*, Manas Ranjan Das** and Sarat Kumar Das* * Civil Engineering Department, National Institute of Technology, Rourkela, Odisha

**Civil Engineering Department, ITER, SOA University, Bhubaneswar, Odisha

Abstract: Inclusion of reinforcements within soil mass increases the bearing capacity and reduces the settlement of soil foundation. In this paper an optimum design of geosynthetic reinforced soil foundation is presented using evolutionary optimization algorithm, genetic algorithm. A design procedure available in literature considering both pullout and rupture failure of geosynthetic reinforcement is used. The genetic algorithm is found to very efficient in identifying the optimum dimension of the reinforced soil foundation. The implementation issue of genetic algorithm parameters is discussed. A parametric study is also made to identify the important soil and reinforcement parameter in achieving the optimum design.

INTRODUCTION

Reinforced soil, or mechanically stabilized soil consists of soil that is strengthened by tensile elements such as metal strips, geotextiles or geogrids. The development of polymeric materials in the form of geosynthetics has brought major changes in geotechnical engineering. The beneficiary effects of soil reinforcement are derived from (a) the increased tensile strength of soil and (b) the shear resistance developed from the friction at the soil reinforcement interfaces. So there is increase in applications of geosynthetics in geotechnical structures such as foundation, embankments, retaining wall etc.

The design of shallow foundation considers two criteria; the bearing capacity and settlement. Bearing capacity generally depends on the strength of the soil while settlement generally depends on the compressibility of soil (Das 2007). In case of weak soil the improvement in bearing capacity and decrease in settlement can be achieved by geosynthetic reinforcement (Shukla and Yin 2006). The analysis of reinforced foundation is considered in terms of pullout and rupture (break out) failure of geosynthetic reinforcement.

Various small scale laboratory experiments were performed on various soils like clay (Sakti and Das 1987) and sand (e.g., Guido et al. 1987; Khing et al. 1993; Yetimoglu et al. 1994) using single or multilayered geosynthetic reinforcement. It was confirmed by most researchers that there was a significant increase in bearing capacity and decrease in settlement of soil reinforced with geosynthetics. The increase in bearing capacity of reinforced foundation is defined in terms of bearing capacity ratio (BCR), which is defined as the bearing capacity of reinforced soil to that of unreinforced soil.

Regarding design of shallow foundation using geosynthetics, Das et al. (1996) proposed procedure regarding strip foundation in geogrid reinforced clay. Wayne et al. (1998) discussed some design issues of geosynthetic reinforced foundation. Shin and Das (2000) conducted small

413

scale laboratory model test to determine the ultimate bearing capacity of a strip foundation supported on sand reinforced with multiple layers of geogrid and proposed a design procedure based on the model study. However, the rupture strength of the geogrid was not taken into consideration while determining the bearing capacity ratio. Michalowski (2004) presented recommendation for design of reinforced foundation using kinematic approach of limit analysis. Both pull out strength and rupture strength was considered and the improvement was presented in terms of bearing capacity ratio. The design of reinforced soil is a trial and error process in which the position, layer and length of the reinforcement is estimated based on the desired BCR value.

Optimization is an integral part of engineering design. Wang and Kulhawy (2008) discussed optimum dimension and design of ordinary reinforced cement concrete shallow foundation. Basudhar et al. (2007) presented an optimization based design of reinforced earth retaining wall. However, to the best of knowledge of the authors such a study on reinforced foundation bed is not available in literature. The optimization algorithm presented in Basudhar et al. (2007) and Wang and Kulhawy (2008) are based on the traditional optimization algorithm. These algorithms have the shortcoming of initial point dependent and the penalty function used for the constrained optimization may distort the true optimum value (Deb 2001). In the recent past evolutionary algorithms like genetic algorithm (GA) (Goh 1999, Das 2005, Cheng et al. 2007), simulated annealing, particle swarm optimization, simple harmony optimization and Tabu search (Cheng et al. 2007) have been used in geotechnical engineering with success.

With above in view, an attempt has been made in this work to use the GA for optimization of reinforced foundation bed in terms of achieving a desired BCR. A parametric study was made to find out the effect of soil properties and tensile strength (Tu)| of geosynthetic reinforcement.

METHODOLOGY The methodology consists of development of the optimization model based on the physical problem and solution of the optimum function using GA. A brief description about the development of optimization problem and implementation of GA in solving the developed model is presented in the following section.

The methodology for reinforced soil foundation as presented in Michalowski (2004) has been considered. A brief introduction about the above method is presented as follows.

The ultimate bearing capacity (q) without reinforcement is given by the Terzaghi equation as

γγBNqNcNq qc 2

1++= (1)

with coefficients N dependent only on internal friction.

A typical footing on reinforced earth foundation is shown in Figure 1.

414

Fig 1: A general footing on reinforced earth foundation (Das 2009) As per Michalowski (2004) bearing capacity of reinforced soil with one layer of reinforcement is given by:

)]2

1()(( )[

11

B

dMNBMnNqMnfNc q

pqccc

Bdr

Mp γµγµ γ

µ+++= ++

− (2)

where μ=soil reinforcement friction coefficient, given as

μ=fb tanφ (3)

fb and fc are bond coefficients and taken as 0.6 Mc, Mq and Mγ are standard bearing capacity coefficients due to reinforcement, B= width of the footing and

Bd = relative depth of reinforcement. Standard bearing capacity coefficients are taken

as functions of φ only (Michalowski 2004)

Nc= (Nq-1) cotφ (4)

Nq= )24

(tan 2 φπ+ e φπ tan (5)

Nᵧ=e φtan11.566.0 + tanφ (6) To extract maximum benefit Mc, Mq, Mᵧ are taken equal to M when the reinforcement intersects the failure mechanism. The coefficient M can be estimated by the following expression M= 1.6(1 +8.5tan1.3φ) (7)

and coefficient Mp can be approximated by the following linear equation

Mp =1.5- 1.25x10-2φ (8)

where φ is in degrees

For two or three layer reinforcement, the bearing capacity equation is presented as follows

415

)]12

1(()( )[

11

1 ∑=

+++++∑=

−=

n

i BdMNBMnNqMnfNc i

qccip

ni B

dMpr µγµ γ

µ

(9)

where n= number of layers, di= depth of ith layer. Coefficient M is approximated with the following expressions M= 1.1 (1+0.6 tan1.3φ) (10) for second layer foundation, and

M=0.9 (1+11.9 tan1.3φ) (11) for third layer foundation. Coefficient Mp approximated as Mp= 0.75-6.25x10-3φ (12) for second layer reinforcement, and

Mp=0.50-6.25x10-3φ (13) for third layer reinforcement (φ in degrees). Bearing capacity ratio with respect to pull out is calculated as

qpr

= BCRp (14)

Bearing capacity ratio with respect to rupture is calculated

qpt

=BCRr (15)

Where

rqc M

BnTtBNqNcNpt +++= γγ

21

(16) n= number of layers and

Mr= 2cos(24φπ

− )eφφπ tan)24( +

(17)

The optimization techniques used in the present study is evolutionary algorithm, genetic algorithm. Though there are limited studies on application of GA to geotechnical engineering problems, a brief discussion about the algorithm is presented here for completeness and the details can be found in Deb (2001).

APPLICATION OF GENETIC ALGORITHM The GA is a random search algorithm based on the concept of natural selection inherent in natural genetics, presents a robust method for search for the optimum solution to the complex problems. The algorithms are mathematically simple yet powerful in their search for improvement after each generation (Goldberg, 1989). The artificial survival of better solution in GA search technique is achieved with genetic operators: selection, crossover and mutation, borrowed from natural genetics. The major difference between GA and the other classical optimization search techniques

416

is that the GA works with a population of possible solutions; whereas the classical optimization techniques work with a single solution. Another difference is that the GA uses probabilistic transition rules instead of deterministic rules. The GA that employs binary strings to represent the variables (chromosomes) is called binary-coded GA. The binary-coded GA consists of three basic operators, selection, crossover or mating, and mutation, which are discussed as follow. In the selection procedure, the chromosomes compete for survival in a tournament selection, where the chromosomes with high fitness values enter the mating population and the remaining ones die off. The selection probability (Ps) determines the number of chromosomes to take part in tournament selection process. The selected chromosomes form an intermediate population known as the mating population, on which crossover and mutation operator is applied. The selected chromosomes are randomly assigned a mating partner from within the mating population. Then, a random crossover location is selected in any two parent chromosomes and the genetic information is exchanged between the two mating parent chromosomes with a certain mating probability (Pc), giving birth to a child (new variable) or the next generation. In binary-coded GA, mutation is achieved by replacing 0 with 1 or vice versa in the binary strings, with a probability of Pm. This process of selection, crossover, and mutation is repeated for many generations (iterations) with the objective of reaching the global optimal solution. The flow chart of the general solution procedure of GA is depicted in Figure 2.

The solutions of the GA representing a set of population are evaluated in terms of fitness. In the absence of constraints, fitness is nothing but the objective function itself. However, similar to natural genetics, GA allows the maximum value to survive, so for minimization the fitness function is defined in any one of the forms as given below.

minmax

11f

F+

=

In the present analysis, a real- coded GA has been used, in which there is no need of coding and decoding the design variables. The real- coded GA with simulated binary crossovers (SBX), polynomial mutations and a tournament selection type of selection procedure have been used, details of which are available in Deb (2001). The GA was implemented using pseudo code available as freeware at http://www.iitk.ac.in/mech/research_labs.htm.

Fig 2: Flow chart for working principles of genetic algorithm (Das 2005)

417

RESULTS AND DISCUSSION

To validate the developed code, the problem as considered in Michalowski (2004) was taken with footing width B=1.2m and the sand under the footing has an internal friction angle φ=35° and unit weight γ=17 kN/m3. The allowable tensile strength of Geosynthetic reinforcement was taken 16 kN/m. The results obtained in the present study and compared with that obtained as per Michalowski (2004) is presented in Table 1.

OBJECTIVE FUNCTION The objective function considered here is the cost of reinforcing the soil with geosynthetics and expressed in US Dollar ($) per meter run. The basic rate/ unit cost of different activities for the construction of reinforced foundation is taken as per Basudhar et al. (2007) and presented in Table 2.

TABLE 1: Validation of present study with Michalowski (2004)

RESULTS OBTAINED BY

REINFORCEMENT WITH ONE LAYER

REINFORCEMENT WITH TWO LAYERS

REINFORCEMENT WITH THREE LAYERS

BCRp BCRt BCRp BCRt BCRp BCRt MICHALOWSKI 1.64 1.35 1.86 1.71 - - GENETIC ALGORITHM

- 1.35 - 1.71 - 2.08

Table 2: Unit cost of various items of reinforced soil foundation

ITEMS UNIT PRICE Cost of earthwork $2.6/m3 Cost of fill $3/1000kg Cost of geosynthetic $(Ta*0.03+2.6)/m2 Engineering and Testing Cost $10/m2

The successful application of GA depends upon the factors like, population size, number of generation, crossover probability (pc) and mutation probability (pm) (Deb 2001). For the present study the number of population considered is 100. The values of number of generation are decided based on the variation of objective function for combination of pc and pm values. Such a study is presented in Figure 3. In this study the cost of construction is considered as the objective function (fitness). It can be seen that for a fixed value of pm (0.07), the minimum objective function depends upon the crossover probability (pc). For the example considered here, the minimum objective function is reached after 30 generation. Similarly for a constant pc value, the number of generation to reach at minimum fitness depends upon the pm values as shown in Figure 4. It was found that, the minimum fitness was observed for pc value of 0.9 after 20 generation. However, it may be kept in mind that the GA parameters are highly problem dependent and one need to tune these parameters to reach at the optimum value.

The variation of the cost with generation (taking pc=0.9 and pm=0.07) is shown in Figure 5.It can be seen that the best fitness (minimum objective function) is almost constant after 20 generations. The variations in best and worst fitness show the diversity in the proportion which is an important aspect o for successful application of GA (Deb 2001).

418

Fig 3: Variation of cost (objective function) with pc with generation number and pm of 0.07.

Fig 4: Variation of cost (objective function) with pm value with generation number and pc of 0.9.

Fig 5: Variation of the cost (objective function) with generation number (taking pc=0.9 and pm=0.07)

VARIATION OF OPTIMUM BCR VALUE

0 20 40 60 80 1000

100

200

300

400

500 Pc =0.95 Pc =0.90 Pc =0.85 Pc =0.80 Pc =0.75 Pc =0.70

Cost

(USD

)

Generation Number

0 10 20 30 40 50 60 70 80 90 1000

50

100

150

200

250

300

350

400

450

Pm=0.10 Pm=0.15 Pm=0.20 Pm=0.25Pm=0.30

Generation Number

Cost

(USD

)

0 10 20 30 40 50 60 70 80 90 1000

100

200

300

400

500

600

700

800

900

1000

1100

1200

1300

Best Fitness Average Fitness Worst Fitness

Generation Number

Cost

(USD

)

419

In the reinforced soil foundation, it is very important to achieve the maximum BCR value with the combination of soil and reinforcement parameter. In this section the objective function is considered as maximization of the BCR value. A parametric study is made to find out the influence of various parameters on the maximization of BCR value. Various parameters considered for the analysis were angle of internal friction of the fill (φ), unit cohesion (c), unit weight of the fill (γ).

To study the variation of the optimum BCR value with angle of internal friction the value of cohesion is taken as 0 and γ =17 kN/m3. The variation of BCR value with φ and ultimate tensile strength of reinforcement is plotted in Figure 6. It can be observed that with increase in the φ value the optimum BCR value increase but at the same time desired Tu is also very high. It can also be observed that there is sudden increase in Tu value with φ value of 450. In most of the field condition the φ value is 30-350. Hence, Figure 6 can be used a guideline for the selection of Tu and φ value for the desired BCR value. The effect of cohesion value on the optimum BCR value is considered for φ = 200 and γ =17 kN/m3. The variation is shown in Figure 7. It can be seen that with increase in cohesion for the optimum value as Tu value decreases the BCR value also decreases with increase in cohesion. It may be mentioned here that the reinforced soil is not effective with high cohesion value. The variation of optimum BCR value with different values of γ is shown in Figure 8 considering cohesion=0 and φ =200. It can be seen that for a fixed value of cohesion and φ value, there is no development in BCR value with increase in γ value. It is also important to mention here that with increase in γ value the desired Tu value increases. This has implication in terms of using light weight backfill material like fly ash, for which the required Tu value will be less than that required for the soil.

Fig 6: Variation of the BCR and geosynthetic tensile strength and internal angle of friction

20 25 30 35 40 45

0

200

400

600

800

1000

2.5

3.03.54.04.5T u (k

N/m

)

BCR

φ (degrees)

420

Fig 7: Variation of the BCR with geosynthetic tensile strength and soil cohesion

Fig 8: Variation of the BCR and geosynthetic tensile strength with unit weight of soil

CONCLUSION

In this study an attempt has been made to apply an efficient optimization algorithm i.e. genetic algorithm for optimum design of reinforced soil foundation. Based on the above study following conclusions can be made:

• GA is found to efficient in isolating the optimum cost configuration of the reinforced soil foundation.

• The optimum value of the objective function found to vary with the GA parameters, crossover and mutation probability.

25 30 35 40 45 50

1500

1550

1600

1650

1700

1750

1800

1850

2.172.18

2.192.202.212.222.232.242.25T u (

kN/m

)

BCR

c (kN/m2)

14 15 16 17 18 19 20 211.0

1.5

2.0

2.5

3.0 BCR Tu

γ (kN/m3)

BCR

100

110

120

130

140

150

160

170

180

190

200

Tu (kN

/m)

421

• Based on the parametric study it was observed that with increase in thevalue the optimum BCR value increase but at the same time desired Tu is also very high.

• With a fixed value of cohesion and angle of internal friction value, the optimum BCR value found to independent of value, but with increase in value the desired Tu value increases.

References Adams, M. T., and Collin, J. G.,(1997). “Large model spread footing load tests on geosynthetic

reinforced soil foundations”, J. Geotech. Geoenviron. Eng., 123(1), pp. 66–72. Basudhar, P. K, Vashistha, A., Deb, K.., Dey, A.,(2007). “Cost Optimization of Reinforced Earth

Walls”, Geotechnical and Geological Engineering, Vol 26(10), pp. 1-12. Cheng, Y.M., Li, L., Chi, S.C.,(2007) “Performance studies on six heuristic global optimization

methods in the location of critical slip surface”, Computers and Geotechnics 34 (6) , pp. 462-484. Das, B.M., (2002). Principles of Geotechnical Engineering, Brookes- Cole, New York (USA). Das, B.M., (2009). Shallow Foundations: bearing capacity and settlement, 2nd edition, Taylor &

Francis Group, London, U.K. Das, S.K.,(2005). “Slope stability analysis using genetic algorithm”, Electronic Journal of

geotechnical Engineering, Vol. 1. Deb, K., (2001). Multi-objective optimization using evolutionary algorithms, Wiley, Chichester, UK. Goh, A.T.C.,(1999). “Genetic algorithm search for critical slip surface in multiple-wedge stability

analysis”, Canadian Geotechnical Journal, Vol. 36, pp. 382-391. Guido, V. A., Knuppel, J. D., and Sweeny, M. A.,(1987). “Plate loading tests on geogrids-reinforced

earth slabs. Proc”., Geosynthetics ’87, Industrial Fabrics Assoc. Int., St. Paul, Minn., Vol. 1, 216–225.

Khing, K. H., Das, B. M., Puri, V. K., Cook, E. E., and Yen, S. C.,(1993).”Bearing capacity of strip foundation on geogrid-reinforced sand.” Geotext. Geomembr., 12, 351–361.

Michalowski, R.L.,(2004).” Limit Loads on Reinforced Foundation Soils”, Journal of Geotechnical and Geoenvironmental Engineering. Vol. 130, No. 4.

Sakti, J. P., and Das, B. M.,(1987). ‘‘Model tests for strip foundation on clay reinforced with geotextile layers.’’, Transportation Research Record 1153, Transportation Research Board, Washington, D.C., 40–45.

Shin, E.C. and Das, B.M.,(2000).” Experimental study of bearing capacity of a strip foundation on geogrid reinforced sand”, Geosynthetics International, Vol. 7, No. 1, pp. 59-71.

Shiwakoti, D.R., Pradhan, T.B.S. and Leshchinsky, D.,(1998). “Performance of Geosynthetic-Reinforced Soil Structures at Limit Equilibrium State”,Geosynthetics International, Vol. 5, No. 6, pp. 555-587.

Shukla, S.K. and Yin, J.H.,(2006). Fundamentals of Geosynthetic Engineering, Taylor & Francis Group, London, U.K.

Wang, Y. and Kulhawy, F.H.,(2008). ”Economic design optimization of foundations”, Journal of Geotechnical and Geoenvironment”, 134: 1097-1105.

Yetimoglu, T., J.T.H. Wu, and A. Saglamer,(1994). “Bearing capacity of rectangular footings on geogrid-reinforced sand.” J. Geotech. Eng., ASCE, 120(12): 2083.

422

ANALYTICAL STUDY ON THE BENEFIT OF SISAL FIBRE REINFORCEMENT OF

EXPANSIVE CLAYEY SUBGRADE USING FEM

Binu Sara Mathew* and Gayathri Mohan** *Department of Civil Engineering, College of Engineering Trivandrum, Kerala

**Department of Civil Engineering, Shri Sant Gadg Baba College of Engineering and Technology, Maharashtra.

INTRODUCTION

Highways constructed and maintained properly play a major role in nation’s development. Among pavement components, subgrade soil is an integral part of pavement, as it provides support to the pavement. Hence subgrade soil and its properties are important in the design of pavement structure. India is a country with varying terrain, soil, climatic and environmental conditions and about 33% of the total land area in India is expansive soils, which is categorised as a poor soil. Expansive soil is typical clay that demonstrates extensive volume and strength changes at varying moisture contents due to their chemical composition. This change in soil volume cause significant structural damage to foundations, including those of pavements. Construction of civil engineering structures on such soil is highly risky because such soil is highly susceptible to differential settlements, having poor shear strength and high compressibility and of very low CBR value and hence considered as a poor subgrade.

Most of the places in the district of Alappuzha in the state of Kerala have problems due to the presence of weak clayey soils that are expansive in nature. Kuttanad, a unique agricultural region in Alappuzha district, lies below mean sea level and is submerged under water for more than a month in every year during rainy season. Construction of pavements or buildings in this region has always been a real challenge and various ground improvement techniques are still being experimented to arrive at a cost effective solution for the same.

Ground improvement techniques generally use locally available material to the maximum and hence considered as an economical solution. The selection of the correct ground improvement technique at an early stage in the design of structures has an important effect on the choice of foundation. Reinforced earth technique is considered as an effective ground improvement method because of its cost effectiveness, easy adaptability and reproducibility. Earth reinforcing techniques continue to make considerable progress, as a result of continued research, technology developments and of the increasing awareness of its environmental and economic advantages.

Presently, the soil reinforcement technique is well established and is used in variety of applications and a modification of this technique, viz., random inclusion of various types of fibres is also considered as an effective soil reinforcement technique. These fibres act to interlock particles and group of particles in a unitary coherent matrix. Randomly distributed fibre reinforcement can be advantageously employed as a ground improvement technique for embankment and subgrade.

NEED OF PRESENT INVESTIGATION

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Good quality road materials are getting scarce and at the same time they are not affordable in many locations because of high cost of haulage from distant sites where they are available. With the aim of constructing pavements of moderate thickness on poor subgrade, soil stabilization and new techniques of construction have been continuously explored. In such cases, natural soils are either treated or reinforced with different kinds of materials to improve their engineering properties.

A plenty of natural materials such as jute, coir, sisal, bamboo, wood, palm leaf, coconut leaf truck, coir dust, cotton and grass, etc., have been experimented as a soil reinforcement material so as to improve engineering properties of poor soil. Sisal fibre is a natural fibre, available in plenty in Kuttanad of Alappuzha District. Limited studies have been carried out on the use of this fibre as soil reinforcement. An experimental investigation was earlier conducted by the same authors using the waste sisal fibres (Binu and Gayathri, 2012) to arrive at the optimum fibre content and aspect ratio. The study was carried out after stabilizing clay with 5% lime and 7.5% of sand by dry weight of soil. The optimum value of fibre aspect ratio and fibre content were obtained as 80and 0.75% respectively and the same is used for the present study also. It is also essential to investigate the efficiency of reinforcement of Kuttanad clay with sisal fibres and its effect on the extension of service life of pavements.

• Objectives of the Study

The objective of the present study is to carry out an analytical study to quantify the benefits of stabilization of Kuttanad clay. The results of the experimental investigations conducted earlier to arrive at the optimum fibre content and aspect ratio have been adopted in the present study. Hence the objective of the study is to conduct an analytical study to bring out the benefit of stabilization of Kuttanad clay using sisal fibres in terms of Traffic Benefit Ratio (TBR) which gives the extension in the service life of pavement due to fibre reinforcement. The study was carried out using Finite Element Modelling (FEM) in ANSYS.

• Materials Used for the Study

The engineering properties of the soil used for the study was determined by standard procedures specified by relevant IS 2720 [part 2], and is shown in Table 1. Lime has proved to be an effective additive for reducing the Atterberg’s limits of clayey soil, and in increasing the stability of soil after compaction and hence 5% hydrated lime was used as an additive for the present investigation. For enhancing the surface friction between clay and sisal fibre, 7.5% of river sand was also added along with optimum quantity of sisal fibres.

Table 1 Properties of Kuttanad Clay (Binu and Gayathri, 2012)

Properties Values

Field Dry Density (g/cc) 1.32

Field Moisture Content (%) 88

Specific Gravity 2.7 Sand content (%) 8 Silt content (%) 52 Clay content (%) 40

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Liquid Limit (%) 100 Plastic Limit (%) 36 Plasticity index (%) 64

Maximum Dry Density (g/cc) 1.23 Optimum Moisture Content (%) 34

Sisal fibre used for the present study was collected as a waste material extracted during colouring process from the manufacture of mats, carpets and rugs from ‘Extraweave’ Company in Aleppey. The properties of sisal fibres, collected from company are shown in Table 2 and the photograph of sisal fibre plant and fibre are shown in Figs. 1and 2 respectively.

Fig. 1 Photograph of Sisal Fibre Plant Fig. 2 Photograph of Sisal Fibre

Table 2 Properties of Sisal Fibre (Extraweave company, Alappuzha)

Property of Fibre Value

Colour White Average diameter (mm) 0.25 Average tensile strength (N/mm2) 405.9 Density (g/cc) 1.45 Unit weight (kg/m3) 962 Specific gravity 0.962

FINITE-ELEMENT MODELING

ANSYS, a finite element software package intended for the two dimensional analysis of deformation and stability of structures was used for the present study. A two-dimensional axi-symetric, elasto-plastic finite-element analysis of the mechanistic pavement model resting on both unreinforced and reinforced subgrade soil was carried out using ANSYS software in order to quantify the benefits of soil stabilization. The extent of deformation, strain, and the stress at the top of subgrade were captured from subsequent run of the model. The layered pavement response due to traffic loading was extracted mechanistically so as to investigate the benefits of reinforcing the subgrade soil in the flexible pavement design.

• Input Data for Finite-Element Modelling

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The Finite-Element (FE) analysis of the pavement system was carried out by using the standard package ANSYS, employing the multilinear-isotropic elasto-plastic hardening model which defines the constitutive relationship of the materials involved. Properties of different pavement layers required for carrying out the FE analysis are the modulus of elasticity, Poisson’s ratio, and the stress-strain(x10-6) data. The initial tangent modulus is needed only to initialize the iterative procedure. Chandra et al. 2008 has reported that confinement in the pavement due to shoulders and surrounding soils is in the range of 26–40 kPa. Hence, triaxial tests were conducted on both unstabilised and stabilised subgrade soils at a confining pressure of 40 kPa so as to determine the modulus of elasticity which are shown in Figs. 3 and 4 respectively. Elastic modulus was calculated from straight portion of stress- strain curve and was found to be 790 and 2317 kPa for unstabilised and stabilised soil respectively.

Fig 3: Stress Strain Curve for Clay Fig 4: Stress Strain Curve for Stabilised Clay

Actual cumulative stress-strain data generated from unconsolidated undrained triaxial test was used in the present FE analysis. Rajesh, 2006 has determined experimentally the Poisson’s ratio of Kuttanad clay as 0.4 and the same was adopted for the present study. Elastic modulus and Poisson’s ratio for the pavement layer materials as shown in Table 3 were selected from the study conducted by Chandra et al. (2008).

Table 3 Elastic Modulus and Poisson’s Ratio for Pavement Layers

(Source: Chandra et al. 2008) • Dimensions of Finite Element Model and Loading

Dimensions of finite element model should be sufficiently large so that constraints imposed at the boundaries have very little influence on the stress distribution in the system. Helwany et al. (1998) discretized a three layer pavement system with a right boundary at a distance of about eight times the loaded radius and adopted a uniform tyre pressure of 550 kPa acting on a circular contact area with a radius of 160 mm. Kwon et al. (2005) considered 76 mm thick asphalt concrete layer and 254 mm thick unbounded aggregate base course resting on the subgrade soil. A uniform tyre pressure of 828 kPa was considered in this study to simulate an overloaded tyre-pavement loading which was applied over a circular area with a radius of 102 mm. For the present study, a uniform pressure of 575 kPa was applied on a circular contact area with a radius of 150 mm as shown in

Parameter Subbase Base DBM BM

E(MPa) 70.12 99.20 269.67 403.33 Poisson’s Ratio 0.30 0.30 0.25 0.25

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Fig. 5. This uniform pressure was supposed to be caused by a single axle wheel load of 40.8 kN (4,080 kg).

• Boundary Conditions for FE Model

For application of a finite element model in the pavement analysis, a five-layered system of infinite extent was reduced to a system having finite dimensions. Fig. 5 shows a typical 2D axisymmetric Finite Element model of the pavement resting on subgrade soil. Roller supports were provided along the axis of symmetry to achieve the condition that both the shear stresses and radial displacements are equal to zero. Similarly, the roller supports were provided along the right boundary which was placed sufficiently far away from the loaded area so as to have a negligible deflection in the radial direction. At the bottom boundary, roller supports were provided, permitting free movement in the radial direction and a restraint was provided to any movement in the vertical direction. In the present study, the right boundary was placed at a distance of 1,750 mm from the outer edge of loaded area, which is more than seven times the radius of the applied load of 150 mm. Eight noded structural elements were used for discretization of layers in the flexible pavement. Boundary conditions adopted for the study are schematically represented in Fig. 5.

Fig 5: Boundary Condition for the FE model

• Benefits of Subgrade Stabilization

A mechanistic-empirical design approach was used in the present study to evaluate the benefits of reinforcing the weak subgrade soils in terms of reduction in layer thickness and

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extension in service life of the pavement. The proposed methodology has a better capability of characterizing different material properties and loading conditions, and has the ability to evaluate different design alternatives on an economic basis. Same pavement section was considered for both unstabilized and stabilized subgrade. Hence soil stabilization would result in more service life of the pavement due to stabilization and has been expressed in terms of Traffic Benefit Ratio (TBR).

Structural failures considered in the design of flexible pavements as per Indian practice are of two types, namely surface cracking and rutting. Cracking is due to fatigue caused by repeated application of load in the bounded layer generated by the traffic. Rutting is developed due to accumulation of pavement deformation in various layers along the wheel path. Horizontal tensile strain developed at the bottom of the bituminous layer or the vertical compressive strains developed at the top of the subgrade, respectively, have been considered as indices of fatigue and rutting of the pavement structure. Since the scope of the study is limited to stabilising the subgrade soils only, rutting has been considered as a failure criterion in this study. Failure criterion for flexible pavement as per IRC 37-2001 is the development of rut depth of 20 mm. The rutting prediction model is given in Eqn. 1.

N20 = 4.1656×10-8 (1/€v) 4.5337 (1) Where,

N20 = Number of cumulative standard axles to produce a rutting of 20 mm €v = Vertical compressive strain at top of subgrade

The vertical compressive strain developed at the top of the subgrade for both unstabilised and stabilised subgrade were evaluated for all these alternatives using elasto-plastic Finite-Element Analysis. The vertical compressive strain at the top of the subgrade was used as the criterion to study the benefit of reinforcing the subgrade soil in terms Traffic Benefit Ratio (TBR) which gives the extension in the service life of pavement due to soil stabilization and was calculated using Eqn. 2.

TBR = NR / NU (2) Where NR and NU are the number of standard axle passes required for producing an allowable

rut depth for reinforced and unreinforced pavement sections.

• Results of Finite Element Modelling

The vertical deformation and the stresses at each layer of pavement at the end of loading were plotted for various cases of reinforcements. Equivalent stress contour and directional deformations for clay subgrade and stabilised clay are shown in Figs. 6 to 9 respectively.

The vertical strain at top of subgrade was obtained foe the following cases: i) for varying thickness of pavement section with varying subgrade material

(un stabilized and stabilized) at same tyre pressure ii) for same pavement section with varying subgrade materials(un stabilized and stabilized)

at same tyre pressure Benefit of these cases were analysed in terms of Traffic Benefit Ratio (TBR) and number of

standard axle passes to create 20mm rut depth (N20

). Benefit calculation was done for cases of same tyre pressure and varying tyre pressure.

(iii) Benefit calculation for varying pavement section with varying subgrade material at same tyre pressure

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Fig. 6 Equivalent Stress Contour for Clay Fig. 7 Directional Deformation Contour for Clay

Fig. 8 Equivalent Stress contour for Fig.9 Directional Deformation Contour for Stabilized Clay Stabilized Clay Vertical strain at top of the subgrade was estimated by FEM modelling on ANSYS package,

by keeping tyre pressure as 575 kPa and the subgrade layer alone was changed as Kuttanad clay and stabilised clay. Number of cumulative standard axles to produce a rutting of 20 mm and the TBR was calculated for these two cases using Eqns. 1 and 2 respectively and are shown in Table 4 and Table 5 respectively.

Table 4: Benefit of Stabilization on same Pavement Section with Unstabilized and Stabilized Subgrade Layer

Material Strain (micro strain) N20

TBR

Clay 0.045 53163 -

Stabilized Clay 0.028 389676 7.3 It can be seen from Table 4 that stabilization has a positive impact on pavement performance

since it increases number of wheel passes required to cause rutting failure and the improvement in Traffic Benefit Ratio indicates the improvement in service life of pavements. Clay stabilized with lime, sand and sisal fibre with optimum fibre content and aspect ratio can improve the service life of clay by about 7.3 times.

(ii) Benefit calculation for varying pavement section with varying subgrade material at varying tyre pressure.

Inorder to study the effect of varying tyre pressure on the strain values, pressure was varied as 575 775, 975 and 1200 Kpa respectively for the unstabilized and stabilized clay. Hence both

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subgrade material and tyre pressure were varied and the result obtained from FEM analysis for the same is given in Table 5. From Table 5 it can be seen that, for tyre pressures of 575 and 775 kPa, the TBR is almost the same as around 10, whereas for higher tyre pressures, there is a drastic decrease in the TBR value. Hence it can be concluded that for best results of sisal fibre stabilization, the tyre pressure should preferably be equal to or less than775 kPa.

Table 5: Effect of Tyre pressure on Strain values of Stabilized and Unstabilized Clay

Tyre Pressure Strain values (Micro Strain) N20

TBR Clay Stabilized Clay

Clay Stabilized

Clay 575 kPa 0.04499 0.0272 53216 521042 9.8

775 kPa 0.068047 0.0410 8154 81077 9.9

975 kPa 0.08568 0.06571 2869 9554 3.3

1200 kPa 0.10536 0.0854 1123 2912 2.6

SUMMARY AND CONCLUSIONS

Road construction over weak soil subgrades has been a real challenge for the highway authorities even today. This study is an effort to stabilise Kuttanad clay using locally available materials and to arrive at a cost effective methodology for pavement construction in this region. Based on the earlier experimental investigations, a fibre content of 0.75% by dry weight of soil and an aspect ratio of 80 have been identified as optimum for sisal fibres. A Finite Element Modelling was done in ANSYS using these results for studying the benefit of stabilisation of Kuttanad clay using sisal fibres in terms of its Traffic Bearing Ratio (TBR). The results showed that stabilisation of Kuttanad clay using sisal fibre is an efficient and economic tool for improving the characteristics as a subgrade soil. From the undrained triaxial test results, it was observed that the elastic modulus of Kuttnad clay increase by 2.9 times due to addition of lime, sand and sisal fibres. By experimenting with the same pavement section over both unstabilized and stabilized subgrade soil, it was observed that the Traffic Benefit Ratio is 7.3 when the clay was reinforced with sisal fibres. Effect of tyre pressure on the benefit of sisal reinforcement was also experimented by varying the former from 575 to 1200 kPa and it was observed that for best results, the tyre pressure should preferably less than or equal to 775 kPa.

References

Binu, S. M. and Gayathri, M. (2012), “Effect of Sisal Fibre Reinforcement on the Performance of Kuttanad Clay as Subgrade Soil”, Proceedings of 13th National Conference on Technological Trends, Aug 10th &11th, 2012. pp. 275-280.

Chandra, S., Viladkar, M. N. and Prashant, P. N. (2008), “Mechanistic Approach for Fibre Reinforced Flexible Pavements”, ASCE (10). pp.1061-1069.

Helwany, S., Dyer, J., and Leidy, J. (1998), “Finite Element Analysis of Flexible Pavements”, Journal of Transportation Engineering, pp: 491–499.

Kown, J., Tutumluer, E., and Kim, M. (2005), “Mechanistic analysis of geogrid base reinforcement in flexible pavements considering unbounded aggregate quality.” Proceedings of 5th International Conf. on Road and Airfield Pavement Technology, Seoul, Korea, pp: 54–63.

Rajesh, R. (2006), “Experimental and Analytical Study on Coir Geotextile’, M.Tech Thesis (Un Published), University of Kerala, Trivandrum.

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COMPACTION AND CBR BEHAVIOR OF CLAY REINFORCED WITH NaOH TREATED

COIR FIBRES

Rakesh Kumar Dutta*, Vishwas Nandkishor Khatri* and V. Gayathri** * Department of Civil Engineering, National Institute of Technology, Hamirpur – 177005, HP, India

**Department of Civil Engineering, Institute of Technology and Management University, Gurgaon, India

Abstract: The paper presents the effect of treated coir fibres on compaction and C.B.R. behavior of clay. Coir fibres in dry condition and treated with sodium hydroxide were used in the study. The coir content was varied from 0.4 to 1.6%. The results indicated that the addition of fibres leads to increase in optimum moisture content and decrease in maximum dry density. The results of C.B.R. test shows that the clay reinforced with treated fibres was able to bear higher loads at any deformation as compared to clay with dry fibres. Also the C.B.R. and Modulus of Subgrade Reaction for different fibre content were highest for clay reinforced with treated fibres.

Keywords: Coir fibre, Treatment, Compaction, C.B.R.

INTRODUCTION

Reinforced soil is a composite material wherein soil is reinforced by the elements which can take tension. A variety of materials are being used as reinforcing materials e.g. metallic elements, geosynthetics and others. Coir fiber is one of natural geosynthetic material and may offer a variety of soil reinforcement applications. India is the first largest country (66% of world production), producing coir fibre from the husk of coconut fruit. The coir fibres (50 to 150 mm long and 0.2 to 0.6 mm diameter) till recently were being spun into coir yarn and then woven to obtain woven nettings. Coir fibers have many advantages such as low specific weight, producible with low investment at low cost and friendly processing. The fibres are also now a days being air laid, needle punched or adhesive bonded to obtain non-woven products or blankets. Like their polymeric counterparts geotextiles can be synthesized for specific applications in civil engineering like erosion control, ground improvement etc. Studies in this direction were initiated at National Institute of Technology, Hamirpur. These studies have broadly indicated that the coir based geotextiles have potential of being used for subgrade improvement. The present study is an attempt to study the effect of inclusion of treated coir fibres on CBR and compaction behaviour of the clay for possible use in subgrade of rural roads in India.

BACKGROUND

Reinforced soil is a composite material wherein soil is reinforced by the elements which can take tension. The incorporation of reinforcement in the soil mass is aimed at either reducing or suppressing the tensile strain which might develop under gravity and boundary forces. As such soils possess very low tensile strength which may be improved significantly by providing reinforcement in the direction of tensile strains. A variety of materials are being used as reinforcing materials e.g. metallic elements, geosynthetics and others. Geosynthetics are the most common reinforcement materials used now days. The cost of this virgin material is high. Civil

431

engineers around the world are hence constantly in search of new alternative materials which are required both for cost effective solutions particularly in developing nations. In this regard, the coir products may offer a variety of soil reinforcement applications.

Prasad et al, (1983) reported that removal of lignin, hemicellulose, silica and pith from fibres results in better interaction with the soil. Shankar et al., (2004) have reported a similar study on coir fibre stabilized lateritic soil and it was found that, in lateritic soils, the CBR value increases up to 10 % by volume of coir fibre added. It may thus be concluded that discrete coir fibre contributes substantially in improving the CBR value of weak subgrade soils. A maximum value of CBR is attained at a specific fibre content corresponding to the specific optimum moisture content attained by the soil-coir matrix. Lekha and Sreedevi (2006) conducted the study on soil reinforced with coir fibres at different proportions to study the changes in optimum moisture content and maximum dry density. Their study reveals that the optimum moisture content is found to increase with the increase in coir fibre content and correspondingly, the maximum dry density is found to decrease. Muntohar (2009) reported that the brittle behavior of soil is reduced using fibres of length 20mm to 40mm. Dasaka and Sumesh (2011) reported that varying the length of coir fibres and content in soil results improvement in strength characteristics. They further reported that length of fibres play a significant contribution in the strength enhancement of soil. However studies relating to compaction and CBR behavior of soil reinforced with dry/treated coir fibres have not been reported so far. The present study is one such attempt to examine the effect of inclusion of dry/treated coir fibres on the optimum moisture content, maximum dry density and CBR for improving strength of subgrade soil.

MATERIAL USED AND EXPERIMENTAL PROCEDURE

The locally available soil was used in this study. The soil is having a specific gravity of 2.67, liquid limit of 23.1% and plastic limit of 11.1 %. The maximum dry unit weight and optimum water content as obtained by standard proctor test was found to be 18.6 kN/m3 and 12.0 % respectively. As per Universal Soil Classification System, the clay was classified as clay of low compressibility (CL).

The coir fibres were obtained from the coir rope (Fig. 1 (a)) procured from the local market. The yarns of the coir ropes were separated and the fibres were cut in the length of 15 mm and the separated fibres are shown in Fig. 1(b). The properties of these coir fibres are reported by Banerjee et al. (2002) and are shown in Table 1. The coir fibres obtained as shown in figure 1 (b) were dipped in sodium hydroxide (0.1N NaOH) solution for 24 hours. After 24 hours, fibres were removed from the beaker and allowed to dry at room temperature for a week. The concentration and composition of chemical used for treatment of coir fibres are given in Table 2.

Fig. 1 Preparation of fibres (a) Coir fibre rope (b) Separated fibres of 15 mm in length

Table 1: Properties of coir fibres (After Banerjee et al., 2002)

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Property Fibres < 100 mm in length Breaking load, N 217.8 Tenacity (cN/tex) 11.5 Modulus (Initial) (cN/tex) 85.9 Modulus offset) (cN/tex) 9.5 Breaking extension, % 41.7 Energy to break (Joules) 0.0062 Thickness in 1/100th mm 13.57 Linear density (tex) 18.9

Table 2: Concentration and composition of NaOH solution used for treatment of coir fibres

Sodium hydroxide Carbonate 2%

Chloride 0.01% Sulphate 0.05% Potassium 0.1% Silicate 0.05%

Zinc 0.02% N/10 solution

For the standard proctor compaction tests on clay the required percentage of coir fibres (0, 0.4, 0.8 and 1.6 % by dry weight of clay) were mixed in soil and water was added as needed to facilitate the mixing and compaction process. For CBR tests on clay reinforced with coir fibre, a thin layer of grease was applied on the internal surfaces of the CBR mould in an attempt to minimize the side friction. The clay with and without coir fibres were compacted on the top of the CBR mould (rigid metal cylinder with an inside diameter of 152 mm and a height of 178 mm) at a respective optimum moisture content by the standard procedure by giving 56 blows of a 25.5 N rammer dropped from a distance of 310 mm. A manual loading machine equipped with a movable base that traveled at a uniform rate of 1.25 mm/min and a calibrated load-indicating device was used to force the penetration piston of diameter of 50 mm into the specimen. A surcharge plate of 2.44 kPa was placed on the specimen prior to testing. The loads were carefully recorded as a function of penetration up to a total penetration of 12.5 mm.

RESULTS AND DISCUSSION

• Compaction Behavior

The dry unit weight and moisture content curves for clay reinforced with varying percentage of untreated, NaOH treated coir fibres are shown in Fig. 2. For the purpose of comparison the compaction curve of pure clay is also indicated in the respective figures. The values of maximum dry unit weight and optimum moisture content (O.M.C.) for clay reinforced with untreated, NaOH treated coir fibres are tabulated in Table 3. A study of Fig. 2 reveals that the optimum moisture content of clay reinforced with both treated and untreated coir fibres increases with the increase in fibre content. For example, the optimum moisture content of clay was 12 % which increased to

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12.6%/12.3% when it was reinforced with 0.4% untreated/NaOH treated coir fibres. The optimum moisture content further increased to 13.3 %/13.1% when the clay was reinforced with 1.6 % untreated/NaOH treated coir fibres. Thus, it can be concluded that the optimum moisture content of clay reinforced with coir fibres increases with the increase in fibre content. Further it is evident that the optimum moisture content of clay reinforced with treated coir fibres is marginally smaller than clay reinforced with untreated fibres. A study of Fig 2 and Table 3 also reveals that the maximum dry density (M.D.D.) of clay reinforced with coir fibres decreases with increase in fibre percentage. For example, maximum dry density of unreinforced clay was 18.6 kN/m³ which decreased to 18.10 kN/m³ when reinforced with 1.6% dry fibres. For clay sample with NaOH

treated fibres the maximum dry density observed for similar fibre percentage (1.6%) was marginally higher (18.2 kN/m³). A similar trend was observed for 0.4 and 0.8 % fibre content as well. Hence it can be concluded that the treatment of coir fibre lead to a marginal decrease and increase in O.M.C. and M.D.D values respectively in comparison with clay reinforced with dry fibres alone.

Fig. 2 Compaction curves for clay reinforced dry and treated coir fibres for fibre content (a) 0.4 % , (b) 0.8 % and (c) 1.6 %

Table 3: The summary of M.D.D. and O.M.C. values for reinforced clay sample

with varying fibre content

17

17.4

17.8

18.2

18.6

19

6 8 10 12 14 16 18

Dry

den

sity

(kN

/m3 )

Water Content (%)

Pure Clay

Clay + 0.4 % treated fibresClay + 0.4 % dry fibres

17

17.4

17.8

18.2

18.6

19

6 8 10 12 14 16 18

Dry

dens

ity (k

N/m

3 )

Water Content (%)

Pure Clay

Clay + 0.8 % treated fibresClay + 0.8 % dry fibres

17

17.4

17.8

18.2

18.6

19

6 8 10 12 14 16 18

Dry

den

sity

(kN

/m3 )

Water Content (%)

Pure Clay

Clay + 1.6 % treated fibresClay + 1.6 % dry fibres

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• CBR Behavior

The load deformation curve for pure clay and clay reinforced with dry and treated fibres as obtained from C.B.R. test is shown in Fig. 3. From this figure it can be seen that the observed load for reinforced soil at any deformation is higher than in case of pure clay. The difference between observed load of reinforced clay and pure clay specimen increases with increase in deformation. This behavior was consistent for different fibre contents. Hence it is quite clear that the reinforced specimen sustains higher load for the same deformation. It should be noted that the observed load at any deformation was highest for clay reinforced with NaOH treated fibres. Thus the stiffness of soil + coir fibre samples can be further enhanced by treating the coir fibres.

The C.B.R. value for different fibre content is indicated in Fig 4. This figure indicates an increase in C.B.R. value with the addition of dry/treated coir fibres to soil. For example the C.B.R. value for pure clay was 3.42 % which was increased to 4.22 % for clay + 0.4 % dry fibres. The C.B.R. value further increased to 7.46 % for clay + 1.6 % dry fibres and it is almost twice of C.B.R. for unreinforced case. The C.B.R. value at all the fibre content was highest for clay + treated fibre specimens. The C.B.R. value for clay + 0.4 % treated fibre was 5.45 % which increased to 8.85 % with the addition of 1.6 % fibres to soil. The increase in C.B.R. value at 1.6 % fibre content as compared to unreinforced case was about 160 %.

• Modulus of Subgrade Reaction

Modulus of subgrade reaction (Ks) is the reaction pressure sustained by the soil sample under a rigid plate of standard diameter per unit settlement measured at a specified pressure or settlement. Modulus of subgrade reaction is obtained corresponding to 1.25 mm penetration from load penetration curve and actual subgrade modulus is obtained after applying correction for plate size. The Modulus of Subgrade Reaction for various fibre content is shown in Fig. 5. For simplicity the Ks value of reinforced soil sample (Ksrein) is normalized with Ks value of pure clay (Ksunrein). This figure reveals that the addition of fibres to soil leads to significant increase in magnitude of Ks. The Ks for pure clay was about 6638.3 kN/m3 which was increased to 15260 kN/m3 and 16456 kN/m3with the addition of 1.6 % dry and treated fibres respectively.

• Pavement thickness

Pavement thickness is calculated by using CBR design chart (recommended by IRC : 37-1970) for 15-45 commercial vehicles per day exceeding 3 tonnes laden weight. Curve B has been used for this much load. The pavement thickness required for subgrade clay reinforced with dry/treated coir fibres is shown in Fig 6. As expected the required thickness for reinforced soil is less as compared to pure clay. The pavement thickness at 1.6 % dry/treated fibre content was 23 cm and 21 cm respectively whereas for pure clay it was 36 cm. Hence the addition of coir fibres to

Fibre content (%)

Clay reinforced with untreated coir fibre Clay reinforced with NaOH treated coir fibre

OMC (%) Dry unit weight (kN/m3) OMC (%) Dry unit weight (kN/m3) 0.4 12.6 18.23 12.3 18.34 0.8 12.9 18.16 12.7 18.19 1.6 13.3 18.10 13.10 18.2

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subgrade may lead to considerable saving in earthwork. Further the saving will be maximum for clay + treated fibre mix.

a)

(b)

Fig 3: Load-deformation curves for clay reinforced dry and treated coir fibres for fibre

content (a) 0.4 % , (b) 0.8 % and (c) 1.6 %

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Fig 4: The variation of C.B.R. value with fibre content for clay reinforced with

dry and treated fibres.

Fig 5: The variation of normalized modulus of subgrade reaction value with

fibre content for clay reinforced with dry and treated fibres.

Fig 6: The variation of pavement thickness with fibre content for clay reinforced with dry and treated fibres.

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CONCLUSION

In the present paper, the compaction and C.B.R. tests on clay was reinforced with dry/treated coir fibres at varying percentage was carried out. On the basis of the results of the experimental investigation and the discussions made in the earlier sections, the following conclusions can be drawn.

• When soil is reinforced with coir fibers, the optimum moisture content increases whereas maximum dry density decreases with the inclusion of dry/ treated fibres to soil. The clay + treated fibres shown marginally higher density and lower optimum moisture content as compared to clay + dry fibre mix.

• The CBR and Ks values for reinforced clay at different fibre content were substantially higher than of pure clay alone. Further the CBR and Ks values for clay + treated fibres were slightly better than clay + dry fibres

• The compaction and C.B.R. properties of reinforced clay obtained from present study will be useful for the village road construction and other ground improvement measure. Further, its use will also provide environmental motivation for providing a means of recycling large quantities of waste coir fibres.

References

Dasaka, S.M. and Sumesh, K.S. (2011),”Effect of Coir Fiber on the Stress––Strain Behavior of a Reconstituted Fine- Grained Soil”, Journal of Natural Fibers, 17 pages.

Lekha, K.R. and Sreedevi, B.G.,”Coir fibre for the stabilisation of weak subgrade soils”, Highway Engineering Lab, NATPAC, Thiruvananthapuram.

Samia,S. M., Hasan,S.M.N., Hossain,M.J. and Hasan, M. (1986) “Chemical modification effect on the mechanical properties of coir fiber” Engineering journal volume 16 issue 2, issn 0125-8281.

Guleria,S.P. and Dutta,R.K. (2011), “Tension and compression behaviour of fly ash- lime-gypsum composite mixed with treated tyre chips,” ISRN Civil Engineering, Vol. 2011, Article ID 310742, 15 pages.

Dutta,R.K., Khatri,V.N. and Gayathri,V. (2012), “Effect of addition of treated coir fibres on the compression behaviour of clay” Jordan journal of civil engineering, volume 6, no. 4, 2012.

Dixit, S. and Verma, P. (2012) “The effect of surface modification on the water absorption behavior of coir fibers” Pelagia research library advances in applied science research, 2012, 3 (3):1463-1465.

Pasupuleti, V.K.R., Kolluru, S.K. and Blessingstone, T. (2012) “Effect of fiber on fly-ash stabilized subgrade layer thickness” International Journal of Engineering and Technology (IJET) Vol 4 No 3.

Putri, E.E., Rao N.S.V.K. and Mannan,M.A. (2005) “Evaluation of modulus of elasticity and modulus of subgrade reaction of soils using CBR test” Journal of Civil Engineering Research. 2012; 2(1): 34-40.

Mohanty, B., Chauhan, M.S. and Mittal, S. (2011), “California bearing ratio of randomly oriented fiber reinforced clayey subgrade for rural roads” Proceedings of Indian Geotechnical Conference Kochi (Paper No. J-354).

Nayak, S.K., Tripathy, S.S., Rout, J. and Mohanty, A.K. (2000),” Coir-Polyester composites: Effect on fiber surface treatment on mechanical properties of composite” International Plastics Engineering and Technology, Vol.04, 2000, pp. 79-86

Prasad, S.V., Paviandthran, C. and Rohatgi, P.K. (1983),” Alkali treatment for coir fibres for coir-polyester composites ”Research regional laboratory, pp 1443-1454.

Ranjan, G., Vasan, R.M. and Charan, H.D.(1996) ” Probabilistic analysis of randomly distributed fiber-reinforced soil” Journal of Geotechnical Engineering, ASCE pp 419-426. 36.

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Rout, J., Nayak, S.S., Misra, M. and Mohanty, A.K. (2001),” Scanning electron microscopy study of Chemically modified coir fibers,” Journal of applied polymer science, vol. 79, pp 1169–1177.

Sik, S. (2009) “Effect of fibre reinforcement and distribution on unconfined compressive strength of fibre reinforced cemented sand” Geotextiles and Geomembranes, pp 162-166.

Al Wahab, R. M., El-Kedrah, M. M. (1995). “Using fibres to reduce tension cracks and shrink/swell in compacted clays.” Geoenvironment 2000, Geotechnical Special Publication No. 46, Y. B. Acar and D. E. Daniel, eds., ASCE, Reston, Va, Vol. 1, 791–805.

Andersland, O. B., Khattak, A. S. (1979). “Shear strength of kaolinite/fibre soil mixtures.” In: Proc., Int. Conf. on Soil Reinforcement, Paris, France, 1, 11- 16.

Babu, G. L. S., Vasudevan, A. K. (2008). “Strength and stiffness response of coir fibre-reinforced tropical soil.” Journal of Materials in Civil Engineering, 20(9), 571-577.

Banerjee, P.K., Chattopadhyay, R. and Guha, A., (2002), “Investigations into homogeneity of coir fibres”, Indian Journal of Fibre and Textile Research, Vol. 27, pp. 111-116.

Casagrande, M. D. T, Coop, M. R., Nilo Cesar Consoli, N. C. (2006). “Behavior of a fibre reinforced bentonite at large shear displacements.” Journal of Geotechnical and Geoenvironmental Engineering, 132(11), 1505-1508.

Dasaka S.M and Sumesh K.S (2011),”Effect of coir fibre on the stress–strain behavior of a reconstituted fine-grained soil”, Journal of Natural Fibres, 17 pages.

Feuerharmel, M. R. (2000). “Analysis of the behavior of polypropylene fibre-reinforced soils.” MSc Dissertation, Federal Univ. of Rio Grande do Sul, Porto Alegre, Brazil (in Portuguese).

Kumar, S., Tabor, E. (2003). “Strength characteristics of silty clay reinforced with randomly oriented nylon fibres.” Electronic Journal of Geotechnical Engineering, 8 (B).

Maher, M. H., Ho, Y. C. (1994). “Mechanical properties of kaolinite/fibre soil composite.” Journal of Geotechnical and Geoenvironmental Engineering, 120(8), 1381-1393.

Mwasha, P. A. (2009). “Coir fibre: a sustainable engineering material for the Caribbean environment.” The College of the Bahamas Research Journal, 15, 36-44.

Nataraj, M. S., McManis, K. L. (1997). “Strength and deformation properties of soils reinforced with fibrillated fibres.” Geosynthetic International, 4(1), 65-79.

Ramesh, H.N., Manoj Krishna K.V. and Mamatha H.V (2010). Compaction and behaviour of lime coir fibre treated black cotton soil. Geomechanics and Engineering-An International Journal, 2(1), 19-28.

Rao, G. V., Balan, K. (2000). “Coir geotextiles - emerging trends.” Kerala State Coir Corporation Limited, Alappuzha, Kerala.

Rao, G. V., Dutta, R. K., Ujwala. D. (2005). “Strength characteristics of sand reinforced with coir fibres and coir Geotextiles.” Electronic Journal of Geotechnical Engineering, 10(G).

Zeigler, S., Leshchinsky, H. I. L., Perry, E. D. (1998). “Effect of short polymeric fibres on crack development in clays.” Soils and Foundation, 38(1), 247-253.

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REINFORCED COAL ASH SLOPE: EXPERIMENTAL INVESTIGATIONS

Vikramjit Singh, K. S. Gill and Amandeep Singh Department of Civil Engineering, Guru Nanak Dev Engineering College, Ludhiana, India.

Abstract: Coal ash is a waste product from thermal power plants which is produced in large quantities estimating 100 million tonnes of coal ash per annum. This waste product possess large disposal problem, so it is commonly used in structural fills to support footings and pavements in low-lying areas which can be one of the cost-effective and environment-friendly solutions to disposal problems. Coal ash being light in weight exerts less pressure on sub grade & high compaction level are some of the advantages of coal ash over coarse granular soils which makes it a better material for slope preparation. On other hand it may not meet the foundation requirement of bearing capacity. Inclusion of geosynthetics reinforcement at different depths improves load bearing capacity of footing. In the present investigation, Laboratory model of coal ash slope is prepared & behavior of shallow footing on the model for single reinforced and unreinforced cases has been studied to check the effectiveness of its use. Detailed results along with graphs and conclusion have been covered which will provide complete understanding of the research work. The results were found to be encouraging.

INTRODUCTION

Reinforced slopes are cost-effective alternatives for construction where the cost of fill, right-of-way, and other considerations may make a steeper slope desirable. Where the soil or ground is not inherently stable it will be prone to failure, so the performance of the existing soils needs to be improved. There are many ways to achieve, but increasingly geogrids are used to reinforce the soils within embankments or slopes. Soils are good in compression and poor in tension. Geogrid reinforcement is good in tension and poor in compression. A composite of these materials offers the benefits of both geogrid reinforcement used in conjunction with the soil enable that soil to perform better than it would in its unreinforced state, accommodating greater loads or standing at steeper angles. Unsurpassed range of geogrid reinforcements maximizes the opportunity to reuse site won materials as backfill to a reinforced slope. This saves on the export and import of materials from site, embracing sustainability and reducing polluting truck movements. Use of coal ash, which is a waste material left after burning of coal in thermal power plants is a better & cost-effective solution to construct a stable slope. Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata of coal mines in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure. This coal is then transported through railways over long distances to thermal power plants. The waste material left after the burning of coal in thermal power plants is called as “Coal ash”. The high temperature of burning coal turns the clay minerals present in the coal powder into fused fine particles mainly comprising aluminium silicate. Coal ash produced thus possesses both ceramic and pozzolanic properties. Coal ash when used in structural fills or embankments offers several advantages over borrow soils. It is light in weight compacted embankment made of coal ash would exert only 50 % of the pressure on a soft subgrade as a fill of equivalent height using coarse granular borrow and again the compaction curve of coal ash is relatively flat thus implying that construction is less sensitive

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to compaction-moisture content than that of the fine grained soils commonly used as structural fill. Coal ash being non-plastic will also solve the problem of dimensional instability as exhibited by plastic soils. Further categories of fly ash are given below:

Fly ash: Fly ash is the finest of coal ash particles. It is called "fly" ash because it is transported from the combustion chamber by exhaust gases. The combustion of powdered coal in thermal power plants produces fly ash.

Bottom ash: Bottom ash is a coarse, granular, incombustible byproduct that does not rises up along with exhaust gases and is collected from the bottom of furnaces. Bottom ash is coarser than fly ash, with grain sizes spanning from fine sand to fine gravel.

Pond ash: Boiler slag and bottom ash are mixed together with water to form slurry, which is pumped to the ash pond area as shown in Figure 2. In ash pond area, ash gets settled and excess water is decanted. This deposited ash is called pond ash.

When pulverized coal is burnt to generate heat, the residue contains 80 percent fly ash and 20 percent bottom ash. The ash is carried away by flue gas collected at economizer, air pre-heater and ESP hoppers. Clinker type ash collected in the water-impounded hopper below the boilers is called bottom ash. The World Bank has cautioned India that by 2015, disposal of coal ash would require 1000 square kilometers or one square metre of land per person. Nearly 73% of India's total installed power generation capacity is thermal, 90% of it is coal-based.India has about 70 thermal power plants and 70 per cent of them burn coal to generate power. Various Indian collieries supply the coal, which is known to have a very high ash content of almost 40 to 45 per cent. India's thermal power plants produce an estimated 100 million tonnes of coal ash per annum. Of this, RTPS (Raichur Thermal Power Station) alone generates about 1.5 million tonnes at 4,000 tonnes daily. Out of this, 80 per cent is fly ash and 20 per cent bottom ash. This ash needs to be disposed of every day. Several factors have impeded coal ash utilization in India, while it is being extensively used globally. Coal-based thermal power stations have been operational for more than 50 years but the concept of developing environment friendly solutions for coal ash utilization is only about 15 years old. Overall coal ash utilization in India stands at a fairly low level of about 15 per cent of the quantity generated.

In the present experimental investigation attempt has been made to study the bearing capacity and settlement characteristics strip footing subjected to central vertical load, resting on reinforced coal ash slope with the help of model test. For this, tests in plain strain condition on a strip footing of seasoned sal wood on unreinforced and single layer reinforced slopes are performed for central vertical load. Tests are planned for geosynthetic (geogrid) as reinforcement material. The tests were conducted by varying the distance of footing to the edge of slope at top surface & embedment ratio. The results obtained from model tests have been verified by available literature.

EXPERIMENTAL INVESTIGATION

• Materials

Coal ash used in the study was Pond ash, collected from “Guru Gobind Singh Super Thermal Plant, Ropar. The maximum dry density and the corresponding optimum moisture content (OMC) were 11.01 kN/m3 and 27.4% respectively. Commercially available Geogrid (SGi-040) 0.27 mm

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thick with 60 mm x 23 mm aperture size wide having single rib tensile strength of 33.9 kN/m in CD & 43.4 kN/m in MD was used as reinforcing elements.

• Test Tank

A rectangular steel tank of size 4650 mm x 2000 mm x 1500 mm was used in the model test. The sides of the tank were covered by thin polythene sheet and a coating of white grease was applied on the polythene sheet to minimize the frictional resistance. To eliminate the lateral deflection under axial load on the footing the longitudinal side walls of the test tank were strengthened by means of metallic stiffeners. The tank sides were rigidly welded with the vertical posts which were tightly fastened to the foundation base. A horizontal cross beam was fixed on the vertical posts to support the loading device across the middle of the tank.

• Model Footing

A strip footing of seasoned sal wood of size 2000 mm x 300 mm and having a thickness of 65 mm was used. The length of the footing was made almost equal to the width of the tank in order to maintain plain strain conditions. The two ends of the footing were polished smooth to minimize the end friction effects. The base of the footing was made rough, to simulate the roughness of actual footing. The load was applied centrally on the footing to avoid tilting of the footing. The load was applied at the centre on the footing through the plunger of hydraulic actuator.

• Preparation of Slope

Roller compaction was used for the preparation of slope. Slope was prepared with dimensions 3200 mm x 2000 mm x 1000 mm inside the test tank having dimensions 4650 mm x 2000 mm x 1500 mm. The pond ash which was transported from Guru Gobind Singh Super Thermal Plant, Ropar was wet enough having moisture content 22 percent. This moisture content was sufficient enough to achieve the 95 percent dry density after compaction in the test tank. Well mixed pond ash was then spread into the tank in five equal layers each 250 mm thick. In order to ensure uniform compaction of each layer a 116 kg smooth towed roller was passed 20(predetermined) times over each pond ash layer so as to attain a final compacted layer of 200 mm thickness. Before placing the next layer, the earlier layer was scratched with sharp edge in order to provide adequate bonding between the consecutive layer and procedure was repeated until the desired height of 1000 mm was reached. For the control of in-situ density before final compaction, few trials of compaction were carried out by varying passes of 116 kg roller & determining in-situ density after each trial of specified no. of passes. After each trial of specified no. of passes, no. of passes were increased & dry density was again determined. Dry density was determined by placing a mould of known volume inside layer of pond ash. After compaction, weight of mould along with compacted ash was known & bulk density was determined. Then dry density was final calculated. This process was repeated till the placement dry density achieved by this procedure was 95% of the standard proctor density. Same procedure was followed for both unreinforced & reinforced cases. Only difference in reinforced case was that after compaction, reinforcement layer was placed at different z/B ratio.

• Loading Arrangement

The loading arrangement used in the experimental investigations is shown in Fig 1.

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Fig 1: Loading arrangement of the experimental set up

1. Data Taker instrument 7. LVDT-1 2. Laptop 8. LVDT-2 3. Loading Frame 9.Model Footing (Wooden) 4. Hydraulic Actuator 10. Ash Slope 5. Loading Cell 11. Compacted Ash Model 6. Cylindrical Loading Piece 12. Connecting Wires

• Experimental Procedure

After the preparation of the slope in case of unreinforced or single layer reinforced case, model footing was placed at specified edge distances (De = 1B, 2B or 3B). Now loading arrangement was done, connections with data taker were done & load cell was placed over the top cylindrical loading column. Piston of the jack was lowered to a level where sufficient space remains available between the load cell & the plunger of jack. The loading beam and Jack were placed into the position at the center of footing. While placing the model footing sufficient care was taken to ensure the axial loading. The two LVDT’s with their stands were fitted at the two corners diagonally of the footing to measure the settlement of the footing during the application of the load. The plunger was lowered and the desired seating load was applied. The initial reading of the loading gauge and LVDT’s were recorded. Loads are applied in equal increments of 5kN. Before each increment of the load, the readings of the loading gauge and LVDT’s were recorded. The procedure was continued upto failure. From the observations of the test, finally a load-settlement curve was drawn and the ultimate bearing capacity of the footing was obtained by using double tangent method. Same procedure was repeated for different z/B ratio ( 0.25, 0.50, 0.75 or1) for single layer reinforced case.

• Test Parameters

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Parameters such as slope angle (β), footing width (B) and no. of reinforcement layer (N = 1) were kept constant. Variable parameters were distance of footing from edge of slope at crest (De) and embedment ratio (z/B). Total number of 15 tests were performed. Out of which 3 tests were for unreinforced case & 12 tests were for single layer reinforced case. The following are the parameters studied in model tests & are shown in Table.No.1.

Table 1: Parameters of test programme

S No.

Type of test

Constant Parameters

Variable Parameters

1. Unreinforced slope B = 300 mm, β = 45o

De/B = 1, 2, 3

2. Reinforced slope single layer (N = 1)

B = 300 mm, β = 45o

z/B = 0.25 De/B = 1, 2, 3

3. Reinforced slope

single layer (N = 1)

B = 300 mm, β = 45o

z/B = 0.50 De/B = 1, 2, 3

4. Reinforced slope

single layer (N = 1)

B = 300 mm, β = 45o

z/B = 0.75 De/B = 1, 2, 3

5. Reinforced slope single layer (N = 1)

B = 300 mm, β = 45o

z/B = 1 De/B = 1, 2, 3

RESULTS AND DISCUSSION

• Bearing Capacity Behaviour

It can be seen from Table No.2 & Fig No.2 that the bearing pressure of the footing increases with the increase in embedment ratio (z/B) up to certain value of z/B = 0.75 and thereafter any further increase in z/B ratio actually decreases the ultimate bearing capacity of the footing. Similar results are obtained for other cases also.

Table 2: BC results of different z/B ratio for De/B=1

z/B ratio UR 0.25 0.50 0.75 1

BC for De/B = 1 56 64 81 93 82

• Effect of De/B ratio for single layer reinforced slope

De/B ratio for single layer reinforced slope has same effect as in case of unreinforced case. Bearing capacity increases with the increase in De/B ratio. Bearing capacity was maximum at De/B = 3. Also from the trial experiments, it was also observed that bearing capacity of a given slope remains almost constant if the edge distance is increased beyond 3B and the footing tends to behave as if it is placed on a level ground. When the footing is placed at sufficient distance away from the slope crest the passive resistance from the slope side to failure wedge under the footing increases and thus increasing the bearing capacity load. Fig No.3 shows load-settlement characterstics of different De/B for z/B = 0.25

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Fig 2: Load-Settlement curves of different z/B ratios for N = 1 & De/B = 1

Fig 3: Load–Settlement curves of different De/B for z/B = 0.25

• Effect of z/B ratio for single layer reinforced slope

When geogrid is placed too close to the footing (z/B<0.5) the reinforcing effect of the geogrid cannot value be fully mobilized due to lack of confinement. On the other hand, when z/B >0.75, the unreinforced zone directly below the footing becomes thicker and as a result a shear failure of the unreinforced zone is likely, thus decreasing the load-bearing capacity. It would appear that the plane of reinforcement acts as a plane of weakness. The bearing capacity of the footing increases with the increase in embedment ratio (z/B) up to certain value and thereafter any further increase in z/B ratio actually decreases the bearing capacity of the footing. The Bearing Capacity ratio (BCR) increases with embedment ratio (z/B) up to certain critical value and thereafter BCR decreases with further increase in embedment ratio as shown in Fig.No.4. It can also be seen that maximum value of BCR is obtained for embedment ratio of 0.75 for almost all the cases of singly

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reinforced pond ash slopes considered in the investigation. Any increase in the embedment ratio (z/B) beyond this value results in decrease of bearing capacity ratio.

Fig 4: BCR vs z/B ratio curves of different De/B ratios for (N = 1)

CONCLUSIONS

• Within the framework of the present investigation, the following conclusions can be drawn.

• Reinforced pond ash slopes are cost-effective alternatives for new construction where good material is not locally available for attaining stable steeper slopes.

• The behaviour of shallow footings on reinforced pond ash slope were greatly affected by distance of footing from the edge of slope (De/B) & embedment ratio (z/B).

• The load carrying capacity of the footing resting on top of a pond ash slope is low for unreinforced case but for reinforced case, there is a improvement in the load carrying capacity of footings located on such slopes.

• The edge distance (De) from the slope crest greatly effects the load carrying capacity of unreinforced as well as reinforced slopes. Bearing capacity of footing increases with increase in edge distance.

• The bearing capacity of the footing increases with the increase in embedment ratio (z/B) up to certain value which is 0.75 and thereafter any further increase in z/B ratio actually decreases the bearing capacity of the footing. The Bearing Capacity ratio (BCR) increases with embedment ratio (z/B) up to certain critical value (0.75) and thereafter BCR decreases with further increase in embedment ratio. Any increase in the embedment ratio (z/B) beyond this value results in decrease of bearing capacity ratio.

References

Choudhary, A.K; Verma, B.P; (2001); (Behavior of footing on reinforced sloped fill); Proceedings, International Conference on Landmarks in Earth Reinforcement, Japan; 535-539.

Gill, K.S; Choudhary, A.K; Jha, J.N; (2010); (Stability of strip footing on reinforced fly ash slop); Proceeding, 6th International Congress on Environmental Geotechnics, 2; 1160-1165.

Gill, K.S; Choudhary, A.K; Jha, J.N; (2010); (Laboratory investigation of bearing capacity behaviour of strip footing on reinforced fly ash slope); Geotextiles and Geomembranes, 28(4); 393-402.

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Gill, K.S; Shukla, S.K; Jha, J.N; Choudhary, A.K; (2011); (Load bearing capacity of footing resting on a multilayer reinforced fly ash slope); Proceedings of Indian Geotechnical Conference, Kochi(paper no. N-055).

Mittal, S; Shah, M.Y; Verma, N.K; (2009); (Experimental study of footing on reinforced earth slope); International Journal of Geotechnical Engineering, 3(2); 251- 260.

Mandal, J.N; Bhardwaj, D.K; (2008); (Study on polypropylene fibre reinforced fly ash slopes); 12th international conference of international association for computer methods and advances in geomechnics, Goa, India; 3, 3778-3786.

Shukla, S.K; Sivakugan, N; Das, B.M; (2011); (A state of the art review of geosynthetic reinforced slopes); International Journal of Geotechnical Engineering; 5(1) , 17-32.

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IMPROVEMENT IN CBR VALUE OF CLAYEY SOIL BY USE OF GEO-GRID LAYERS

Rajiv Kumar, Gurdeepak Singh and BS Walia

Abstract: Soil stabilisation broadly refers to any chemical or mechanical treatment given to a mass of soil to improve its engineering properties. Lime, fly ash and cement are some commonly used chemical stabilization materials, while geotextile and geo-grids are examples of mechanical soil stabilizers. The paper summarizes the results of a series of laboratory CBR tests conducted on fine grained soil for unreinforced and reinforced with cement and geo-grid layers. The cement up to 5% and three layer of geo-grid is used as a re-inforcing agent provided at the optimum position in subgrade. It is obtained from the result that there is considerable improvement in California Bearing Ratio (CBR) of sub-grade due to geo-grid (3-layers at optimum position) reinforcement. Without reinforcement (Geo-grid) the soaked CBR value was 3.3% and when 3-layer of geo-grid was placed at optimum position in the subgrade the CBR value increases up to 17.2%.

INTRODUCTION

The soil is basically unconsolidated mineral or organic material on the immediate surface of the earth that serves as a natural base for the foundation of various civil engineering works. Generally the natural soils are not ready to work on them, some improvement require in the form of stabilisation of soil. Soil stabilization is the process of improving the engineering properties of the soil and makes them stable. In broad sense, stabilization includes compaction, pre-consolidation, drainage and many other processes. Soil stabilization is used to reduce the permeability and compressibility of the soil mass in earth structure and to increase its shear strength. Soil stabilization is required to increase the bearing capacity of foundation soils. The principles of soil stabilization are used for controlling the grading of soils and aggregates in the construction of bases and sub-bases of the highways and airfields. There are no of methods of soil stabilization like mechanical stabilization, cement stabilization, lime stabilization, bituminous stabilization, chemical stabilization, thermal stabilization, electrical stabilization, stabilization by grouting technique and stabilization by geo-synthetic material (geo-textile, geo-grids etc.).Geo-synthetic materials are used as a separator at the subgrade- pavement interface to prevent the entry of pavement material into the subgrade or subgrade material in to the pavement material. Geo-synthetics are man-made materials used to improve soil conditions. The word is derived from: Geo = earth or soil + Synthetics = man made Geo-synthetics are typically made from petrochemical-based polymers (“plastics”) that are biologically inert and will not decompose from bacterial or fungal action. The work describes the beneficial effects of reinforcing the sub-grade layer with 3-layer of geo-grid at different positions and thereby determination of optimum position of reinforcement layers. The optimum position of placing the geo-grid layers was determined based on California Bearing Ratio test (CBR value).

EXPERIMENTAL PROGRAMME

• Materials Used

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The fine grained soil used in the investigation was natural soil collected from the natural drain passing through the Nilokheri (Karnal).The index properties: liquid limit, plastic limit and plasticity index were determined. The various physical properties of the soil and the reinforcing agent (geo-grid layers) used in the investigation are summarized in Table 1& 2 respectively.

TABLE 1: Physical Properties of Soil

Sr. No Properties Value/ characteristics 1 Colour Light gray 2 Natural W.C 8.0% 3 Liquid limit 47.0% 4 Plastic limit 37.0% 5 Plasticity index 10 6 Maximum dry density 1.48 g/cc 7 O.M.C (%) 24.92% 8 Specific gravity 2.50 9 CBR value 3.3%

TABLE 2: Properties of Geo-Grid

Sr. No Properties Value/ characteristics 1 Mesh aperture size ( mm 25.4mmx25.4mm 2 Elongation ≤13% 3 Tensile Strength 100KN/m2

SAMPLE PREPARATION AND TESTING

The CBR tests were conducted with unreinforced as well as reinforced soil specimen. The sample compacted at maximum dry density and corresponding to the optimum moisture content for CBR test. For the purpose of reinforcing the soil specimen, geo-grid were cut in the form of a circular disc of diameter 147mm (mould dia. 150mm) to avoid separation in the specimen. The geo-grid layers were provided at optimum position at 50mm, 75mm and 100mm from the bottom of CBR testing mould.

The soil sample is compacted in the mould to the required dry density using static compaction. After compacting the soil in lower portion of the mould, reinforcement was placed inside the mould at the specified position and then the required amount of soil was compacted over it. After compaction of the soil in the lower portion of the mould, reinforcement was placed inside the mould at the specified position and then the required amount of soil was compacted over it. The process was repeated for other layers also till all the layers are placed in position within the specimen and finally the top surface was made level. A filter paper and a perforated metallic disc with adjustable stem were placed on the top of the compacted specimen. The whole mould assembly was then transferred to a soaking tank for soaking under water for the period of 96 hours.

After 96 hours of soaking period the whole mould assembly was then transferred to a motorized load frame to conduct the CBR test. The penetration plunger was seated at the centre of the specimen and a seating load of 40N was applied. The dial gauge of the proving ring as well as the penetration dial gauge was set to zero reading prior to application of the load. The load was

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then applied through the penetration plunger at a constant rate of strain (1.20mm/minute).Finally load- penetration curves were drawn and all the specimens were tested in a similar manner.

RESULTS AND DISCUSSION

It is clear that considerable amount of increase in CBR value of soil with geo-grid reinforcement, for example, in case of unreinforced soil the CBR value is 3.3% and with geo-grid reinforcement the CBR value increases to 8.8%. The highest increase in the CBR value was achieved when geo-grid was placed at 100mm depth from the bottom of the specimen. The results are shown in Table no. 3 &4. The considerable amount of increase in CBR value of soil with 3-layer of geo-grid reinforcement was observed up to 17.2%.

TABLE 3: Results of CBR Tests for Different Positions Of Geo-Grids Layer

Sr. No Geo-grid from bottom CBR value (%) 1 At 25mm 5.2 2 At 50mm 6.2 3 At 75mm 7.5 4 At 100mm 8.8

TABLE 4: Results of CBR Tests For 3-Geo-Grid Layers

Fig 1: load v/s penetration curve)

Fig 2: load v/s penetration curve)

Sr. No Position of Geo-grid layers CBR value (%) 1 100mm, 75mm, 25mm 14.8 2 100mm, 75mm, 50mm 17.2

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CONCLUSIONS

Following conclusions are drawn from the present investigation:

• The CBR of a soil increases up to nearly three times (CBR value 8.8%) when it is reinforced with a single layer of geo-grid. The amount of improvement depends upon the type of soil and position of geo-grid. The optimum position for single layer of geo-grid is at 100mm from the bottom of CBR test mould.

• The CBR value of the soil increases significantly with increase in number of reinforcing layers (when 3-layer geo-grid, CBR value 17.2%) and their relative position within the soil and type of reinforcement. The optimum postison for 3-layer geo-grid is at 100mm, 75mm and 50mm from the bottom of CBR test mould.

• The results indicate that the use of geo-grid as a reinforcing agent in the subgrade is effective to increase the CBR value but the optimum value can be achieved by providing the geo-grid layer at the top surface of sub-grade. The CBR value can also improve by providing the two or more geo-grid layers as shown in result section.

References

Gosavi, M., Patil, K.A., Mittal, S. and Saran, S. (2004), “Improvement of properties of fine grained soil subgrade through synthetic reinforcement”, IE(I) J, 84, 257-262.

Nejad, F. M. and small, J.C. (1996), effect of geo-grid reinforcement in model track tests on pavements. Journal of transportation engineering, ASCE, volume 122(6), pp 468-474

Pandian,N.S.,Krishna,K.C.& Leelavathamma B., (2002), Effect of Fly Ash on the CBR behaviour of Soils , Indian Geotechnical Conference , Allahabad , Vol.1,pp.183-186.

Pardeep Singh and K.S. Gill (2012) “ CBR improvement of clayey soil with geo-grid reinforcement”, Internation Journal on Emerging Technology and Advanced Engineering, Volume 2, Issue 6, June 2012.

White, D. W., Jr. (1991). “Literature Review on Geotextiles to Improve Pavements for General Aviation Airports,” Technical Report GL-91-3, U.S. Army Engineer Waterways Experiment Station, Vicksburg, Mississippi

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EXPERIMENTAL INVESTIGATION ON SLOPE STABILITY USING SOIL NAILING

TECHNIQUE

S. Boobathi Raja, M. Ganeshram and A.Kavitha Erode Sengunthar Engineering College, Erode-57. TN.

Abstract: Landslides, one of the major catastrophes, always cause a major problem by killing hundreds of people every year besides damaging the properties and blocking the communication links in hilly areas like Nilgiris. This paper demonstrates the feasibility of utilizing soil nail walls for stabilization of active landslides, extending the application of soil nailing beyond its traditional scope of stabilization of cut slopes or for potentially unstable slopes. This paper deals with one of the land sliding areas TANTEA colony near Tiger hill in NILIGIRIS. The slope was 4.75 m high, 9 m wide, and 33 deg to the horizontal. Site conditions, soil properties providing the suitability of this technique are described. SPT N values ranges from 9 to 15. Owing to the recent developments in technology, this study benefits from SNAILZ. The reinforcement details & factor of safety are determined using SNAILZ software. the optimum number of bars, diameter, spacing, length, inclination, is determined using this software. The factor of safety of the original slope before using nails is found to be 0.69. Five numbers of 25 mm diameter bars are used and the factor of safety is increased to 2.7. The different orientation of reinforcement such as 150,100, 50, 00,-50,-100 is used and the corresponding factor of safety is found as 0.69, 1.06,1.69, 1.84, 2.13, 2.25 respectively and the optimum length of the bar is found to be 1.67m by using SNAILZ software.

Key words: Slope stability, soil nailing, SNAILZ, Optimum soil nails walls, factor of safety.

INTRODUCTION

Soil nailing consists of the passive reinforcement (i.e., no post-tensioning) of existing ground by installing closely spaced steel bars (i.e., nails), which are subsequently encased in grout. As construction proceeds from the top to bottom, shotcrete or concrete is also applied on the excavation face to provide continuity. Soil nailing is typically used to stabilize existing slopes or excavations where top-to-bottom construction is advantageous compared to other retaining wall systems. For certain conditions, soil nailing offers a viable alternative from the viewpoint of technical feasibility, construction costs, and construction duration when compared to ground anchor walls, which is another popular top-to bottom retaining system.

CONSTRUCTION SEQUENCE

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Fig 1: Basic elements of a soil-nailed system

Fig 2: Fundamental mechanism of a soil-nailed system

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Fig 3: Load transfer concept in soil nails walls

Fig 4: Typical diagram showing nailing arrangement in walls

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ADVANTAGES OF SOIL NAILING

• Using top down construction methods with each subsequent row of nails providing both temporary and long term support, the need for costly temporary works is avoided.

• Existing structures and embankments can be stabilized without re-building, saving costs and maintaining serviceability, for example existing railways embankments.

• Creates less noise and traffic obstructions. A more predictable degree of soil improvement

• It connects the active and passive zone and provides internal resistance against sliding. • It is cost effective than other retaining structures.

SITE SELECTED FOR THE PROJECT

Landslides are affect at least 15 per cent of the land area of India—an area which exceeds 0.49 million km2. Government of India reveals that the Nilgiris district of Tamil Nadu state is one of the severe to very high landslide hazard prone areas of India.

Based on the site reconnaissance we have selected TNT LABOUR COLONY, near Tiger hill in COONOOR, one of the land sliding areas has been selected for this project under the guidance of geologist Mr.Bankaj Jaswal., Senior scientist., GEOLOGICAL SURVEY OF INDIA. who deals with the landslides in Niligris district.

SOIL CHARACTERISTICS AND INDEX PROPERTIES

The soil characteristics of the soil sample is given below

S. No Characteristics Results

1 SOIL CLASSIFICATION Silty Clay

2 LIQUID LIMIT 42.2%

3 PLASTIC LIMIT 25%

4 SHRINKAGE LIMIT 27.27%

5 FRICTIONAL ANGLE 0o

6 UNCONFINED COMPRESSIVE STRENGTH 165.78KN/M3

7 UNIT WEIGHT 17.71KN/M3

8 SPT(N) 9

9 OPTIMUM MOISTURE CONTENT 19%

10 ORGANIC CONTENT 10%

11 PLASTICITY INDEX 17.2

TOPOGRAPHY OF THE SITE SELECTED

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SLOPE STABILITY ANALYSIS USING SNAILS SOFTWARE

• Input parameters for snails software

WALL GEOMETRY Vertical Wall Height =3m Wall Batter = 0o First Slope angle from Wall crest. = 0o

First Slope distance =6m Second Slope angle from 1st slope. = 90 o Second Slope distance =3m SURCHARGE 1st slope Begin Surcharge - Distance from toe = 2m 1st slope End Surcharge - Distance from toe = 5m 2nd slope Begin Surcharge - Distance from toe = 9m 2nd slope End Surcharge - Distance from toe = 14m 1st slope Loading Intensity - End = 10 kN/m 1st slope Loading Intensity - Begin = 10 kN/m 2nd slope Loading Intensity - End = 20 kN/m 2nd slope Loading Intensity - Begin = 20kN/m SOIL PARAMETERS Unit weight (γ) =17.71 kN/m3 Cohesion(c) =8.2 kPa Frictional angle (ϕ) = 0o Bond stress =100 kPa SEARCH LIMIT The Search Limit is from 0.0 to 1.6 m You have chosen NOT TO LIMIT the search of failure planes to specific nodes. REINFORCEMENT PARAMETERS Number of Reinforcement Levels = 5 Length of Reinforcement =2.2m Horizontal Spacing = 0.8m

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Vertical spacing of 1st nail =0.25m Vertical spacing of other nails =0.65m Diameter of reinforcement =22mm Diameter of Grouted Hole =35mm Yield Stress of Reinforcement =415MPa Punching Shear =30kN

OUTPUT FOR SLOPE STABILITY WITHOUT NAIL

Fig :Output for slope stability with nail

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• Effect of inclination of nail on FoS

By giving various inclined angle value for nail, the SNAILZ software has give the following factor of safety values from the table below, we can take the inclined nail value as -10 o

Inclination of the nail Factor of safety

-10o 2.25

-5 o 2.13

0 o 1.84

5 o 1.69

10 o 1.06

15 o 0.69

• Effect of length of the reinforcement to obtain optimum reinforcement

To get the optimum reinforcement we have to keep the inclined nail value as a constant and we have to change the length of the reinforcement, to get the factor of safety value more than 1.5 Finally we have to take the length of the reinforcement, which gives the factor of safety value nearly 1.5 .The following factor of safety values are taken for different length, by the inclined angle value as -10o.

LENGTH OF NAIL AND THEIR FACTOR OF SAFETY

Length of nail (m) Factor of safety value

2.6 2.67

2.4 2.47

2.2 2.25

2.0 2.02

1.8 1.79

1.7 1.68

1.6 1.22

FACTOR OF SAFETY FOR OPTIMUM LENGHT REINFORCEMENT:

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CONCLUSION

The following conclusions are drawn from the experimental analysis of TANTEA colony, Niligiris.

• SNAILZ software recommended by CALTRANS is used for the analysis of slope stability.

• The factor of safety of the slope without using nails is found as 0.66 • The stability is analyzed for varying inclination of the nail, -100 gives the maximum

factor of safety as 2.67. • For the -100 the length of the bar is reduced, it is concluded that the optimum length of

the bar is found as 1.7 and the corresponding factor of safety is 1.68 • The factor of safety is increased four times after using this soil nailing technique. • The results provide the effect of soil nailing in the slope stability. • It is concluded that for the negative orientation of the bar gives maximum factor of safety

than the positive orientation.

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INVESTIGATIONS ON CRUMB RUBBER MODIFIED CONCRETE:

AN OVERVIEW

Parveen, Sachin Dass and Ankit Sharma Department of CIVIL Engineering, DCRUST, Sonipat, India

Abstract: The disposal of used tires is a major environmental problem throughout the world which causes environmental hazards. Crumb rubber is a waste material that is ideal for use in concrete applications. The aim of this study is achieved to use of rubber waste as partial replacement of fine aggregate to produce rubberize concrete in M30 mix. Different partial replacements of crumb rubber (0, 5, 10, 15 and 20%) by volume of fine aggregate are cast and test for compressive strength, flexural strength, split tensile strength and stress-strain behavior. The results showed that there is a reduction in all type of strength for crumb rubber mixture, but slump values increase as the crumb rubber content increase from 0% to 20%. Meaning that crumb rubber mixture is more workable compare to normal concrete and also it is useful in making light weight concrete. It is recommended to use the rubberized concrete for non structural applications.

INTRODUCTION

Large quantities of scrap tires are generated each year globally. This is dangerous not only due to potential environmental threat, but also from fire hazards and provide breeding grounds for rats, mice, vermin’s and mosquitoes (Naik and Singh, 1991; Singh, 1993). Over the years, disposal of tires has become one of the serious problems in environments. Land filling is becoming unacceptable because of the rapid depletion of available sites for waste disposal. In order to prevent the environmental problem from growing, recycling tire is an innovative idea or way in this case. Recycling tire is the processes of recycling vehicles tires that are no longer suitable for use on vehicles due to wear or irreparable damage (such as punctures). The cracker mill process tears apart or reduces the size of tire rubber by passing the material between rotating corrugated steel drums. By this process an irregularly shaped torn particles having large surface area are produced and this particles are commonly known as crumb rubber.

It has been reported by Hernandez-Olivares and Barluenga (2004) that the addition of crumb tire rubber to structural high strength concrete slabs improved fire resistance, reducing the spalling damage by fire. Yang et al. (2001) concluded in their research that rubberized concrete can successfully be used in secondary structural components such as culverts, crash barriers, sidewalks, running tracks, sound absorbers, etc. However, most of the developing third world countries have yet to raise their awareness regarding recycling of waste materials and have not developed effective legislation with respect to the local reuse of waste materials. Building on previous research carried out internationally, this study may provide the technical information necessary to improve local awareness of the reuse of crumb rubber as a substitute for natural aggregates in the production of concrete. The proposed work presents an experimental study of effect of use of solid waste material (crumb rubber) in concrete by volume variation of crumb rubber. One of the objectives of this paper is to make these data regarding the basic properties of

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modified concrete using crumb rubber in the concrete mix available to aid in the development of preliminary guidelines for the use of crumb rubber in concrete.

EXPERIMENT PROGRAM

• Crumb Rubber

The crumb rubber achieved after different processes has a nominal size between 4.75mm to less than .075mm. The crumb rubber used in this study was obtained from a local industrial unit in India. The crumb rubber was used in the concrete mix to partially substitute for fine aggregates (sand) in various percentages of 0%, 5%, 10%, 15% and 20%.

Fig 1: Crumb Rubber.

• Raw Material Used in investigations

The raw materials used for the preparation of the concrete mix consist of Ordinary Portland Cement (43 grade), natural fine aggregate and coarse aggregates taken from crushed limestone, all of which were supplied from natural local resources in India. Tap water at room temperature was used in all mixes. The cement was tested in accordance with the methods of test specified in IS: 12269-1989. For each crumb rubber percentage, five batches of concrete were prepared. Concrete with no additives was designated as the control mix. Three mix ratios of cement, water, fine, and coarse aggregates were used to achieve a workable concrete for a typical in situ concrete in order to achieve the high strength mix following IS 10262:1982

Table 1: Physical properties of OPC-43 grade tested as per IS 12269-1989.

Parameter Test value (N/mm2) IS 8112: 1989 Recommendation

Compressive strength 1. 3 days 2. 7 days 3. 28 days

24.4 34.9 49

23 (Minutes) 33 (Minutes) 43 (Minutes)

Specific gravity 3.14 3.15

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• Specimens Preparation and Testing

In order to prepare the recycled crumb rubber concrete specimens, fine aggregates were replaced by waste materials of crumb rubber in several percentages (0%, 5%, 10%, 15%, and 20%) in separate concrete mixes. The sand used was cleaned from all inorganic impurities and the sand, which passed through 2.36 mm sieve and retained on 150micron had been used. For each mix, cubes of 150 X 150 X 150 mm, cylinders of 150 mm diameter by 300 mm height, and small beams of 100X 100 X 500 mm were prepared. All specimens were fabricated and then cured in water for 28 days in accordance with Indian Standard 10262. For each concrete mix, slump tests were performed and recorded at the casting time of the specimens. After 24 hours of casting cubes, beams and cylinders were taken out from the mould and then submerged in water tank for curing. A Universal Testing Machine with a maximum load capacity of 2000 KN (load accuracy within ±0.5%) was used for cubes and cylinders testing. After curing, specimens were tested for compressive strength, split tensile strength, and flexural strength in accordance with IS specified procedures.

Fig 2: Experimental Setup for Testing of Beam specimen.

RESULTS AND DISCUSSIONS

• Compressive Strength

The effect of crumb rubber on concrete compressive strength is given in Figures 3.1. As expected, the higher the rubber content in the mix, the higher the reduction in compressive (fc) strength. Detailed examination of the Figure shows that increasing the crumb rubber upto 10% exhibited a linear relationship between the increase of crumb rubber and the compressive strength, showing a loss of about 24% of the compressive strength at 10% rubber content. Therefore, this result limits the use of the modified concrete when strength is the prime requirement.

• Flexural Strength

A primary concern in designing concrete for use in highway applications is the flexural strength of concrete. Its knowledge is useful in the design of pavement slabs and airfield runway as flexural tension is critical in these cases. The flexural strength or the modulus of rupture of concrete is an indirect measure of the tensile strength. The value of modulus of rupture depends upon the dimensions of the beam and above all on the arrangement of the loading. It is observed that with the increase in the crumb rubber, the flexural strength decreases. However, it is noticed

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that at the later age rate of strength reduction, due to increase in percentage of crumb rubber was steeper than that of the compressive strength. From figure 3.2, it can be concluded that, with the large percentage replacement of fine aggregates, flexural strength decreases drastically.

Fig 4: Variation of Compressive Strength at 7 And 28 Days V/S percentage of Crumb Rubber as

Replacement for FA.

Fig 5: Variation of Flexural Strength at 7 And 28 Days V/S percentage of Crumb Rubber as

Replacement for FA.

• Stress-Strain Behaviour

The stress–strain behaviours of the specimens containing rubber of upto 10% behave in a similar trend to the control specimen, but having a smaller peak. From the figure, it can be observed that there is linear increase of stresses until it reaches its peak before energy is released by specimen’s fracture. For this case, the specimens behaved like a brittle material of which the total energy generated upon fracture is elastic energy. However, nonlinear behavior is seen for the other two specimens containing 15% and 20% rubber. Here, once the peak stress is reached, the specimen continues to yield, as represented by the branch-line. This behavior is similar to the behaviour of the tough materials having most of its energy generated upon fracture as plastic energy.

• Others properties

Table 2: Physical properties of the rubberized concrete

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Crumb rubber (%)

Slump (mm)

Compressive strength(N/mm2)

Flexural strength(N/mm2)

Split tensile strength(N/mm2)

0 45 36.2 4.6 3.4 5 48 32.2 4.1 3.3

10 49 27.7 3.3 3.1 15 40 24.8 2.8 2.9 20 35 22.7 1.4 2.7

Fig 6: Relationship between Stress And Strain for Different Rubber Contents.

It can be noted from the above table that with increase in the crumb rubber the tensile strength decreases. The decrease in the strength is due to nonpolar action of the rubber particles which attract air and repels water. The split tensile strength of the concrete decreases about 30% when 20% sand is replaced by crumb rubber.Failure of plain and rubberized concrete in compression and split tension shows that rubberized concrete has higher toughness. The failed samples containing 15% and 20% fine aggregate substitution with rubber appeared like a true crushing resulting in a post failure material that was sponge-like and elastic in nature. It can be noted that with increase in the crumb rubber upto 10%, the slump value increases after that it started decreasing. The increase of the crumb rubber content in the mix resulted in an increase in the slump. At rubber contents of higher than 10% (10% by fine aggregate volume), the slump decreases.

(1) Control Prism (2) Rubberized Prism

Fig 7: Flexural Tensile Strength Samples For Control Concrete And Rubberized Concrete.

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CONCLUSIONS The test results of this study indicate that there is great potential for the utilization of waste tyres in concrete mixes in several percentages, ranging from 5% to 20%. Based on present study, the following can be concluded:

Concrete with higher percentage of crumb rubber possess high toughness The slump of the modified concrete increases about 1.08%, with the use of 1 to 10% of crumb rubber. Energy generated in the modified concrete is mainly plastic. Stress strain shows that concrete with a higher percentage of crumb rubber possess high toughness, since the generated energy is mainly plastic.Failure of plain and rubberized concrete in compression and split tension shows that rubberized concrete has higher toughness.The split tensile strength of the concrete decreases about 30% when 20% sand is replaced by crumb rubber. The flexural strength of the concrete decreases about 69% when 20% sand is replaced by crumb rubber. The compressive strength of the concrete decreases about 37% when 20% sand is replaced by crumb rubber.For large percentage of crumb rubber the compressive strength gain rate is lower than that of plain concrete. With the addition of the crumb rubber, the reduction in strength cannot be avoided. However, these data provide a preliminary guideline of the strength-loss of locally produced modified concrete in comparison with the conventional concrete of 30 MPa targeted strength. References Hernandez-Olivares and Barluenga (2004) Fire performance of recycled-filled high strength concrete,

Cement and Concrete Research 34 (2004) 109– 117. IS: 383 - 1970, "Coarse and Fine· aggregate from natural sources for concrete," Indian Standard

Institution, New Delhi. IS: 8112 - 1976, "High Strength ordinary Portland cement," Indian Standard Institution, New Delhi. IS: 2430 - 1969, "Methods for sampling of aggregates for concrete," Indian Standard Institution, New

Delhi. IS: 2386 - 1963, "Methods of tests for aggregates for concrete," Indian Standard Institution, New

Delhi. IS: 516 - 1959, "Method of test for strength of concrete," Indian Standard Institution, New Delhi. IS: 10262 - 1982, "Recommended guidelines for concrete mix design," Indian Standard Institution, New

Delhi Nehdi, M. and Khan, A., “Cementitious Composites Containing Recycled Tire Rubber: An Overview of

Engineering Properties and Potential Applications,” Cement, Concrete, and Aggregates, CCAGDP.

Wesam Amer Aules (2011) Utilization of Crumb Rubber as Partial Replacement in Sand for Cement Mortar. European Journal of Scientific Research.

Yang, S., Kjartanson, B., Lohnes, R., (2001), Structural performance of scrap tire culverts. Canadian Journal of Civil Engineering

465

BEARING CAPACITY ANALYSIS OF STRIP FOOTINGS ON REINFORCED SLOPES:

NUMERICAL APPROACH

Amanpreet Kaur Department of Civil Engineering, Rayat Bahra Institute of Engineering and Nano Technology, Hoshiarpur

Abstract: This paper presents the results of a numerical analysis carried out on both reinforced and unreinforced earth slopes loaded with a rigid strip footing. Numerical analysis was carried out using a commercial finite element program PLAXIS version 8 (Brinkgreve and Vermeer 1998). The analysis was conducted by varying different parameters such as depth of embedment of reinforcement layer, distance of the footing from the edge of the slope at crest and type of reinforcement. Two types of soils (sand and silty soil) and three different types of geosynthetics were used in the study. The objectives of this study were to determine the influence of geosynthetic reinforcement on the bearing-capacity characteristics of a footing on slope and obtain an optimum depth of embedment of geosynthetic reinforcement layer. The results of the analysis indicate that pressure-settlement behaviour and ultimate bearing capacity of the footing resting on top of an earth slope can be considerably improved by inclusion of a reinforcing layer at appropriate level in slope fill. It is also shown that for both reinforced and unreinforced slopes bearing capacity increases with increase in the edge distance. Based on results of numerical study, the critical value of embedment depth of geogrid layer for maximum reinforcing effects was established.

INTRODUCTION A reinforced soil foundation consists of one or more layers of a geosynthetic reinforcement and controlled fill placed below a footing to create a composite material with improved performance. The use of geosynthetics to improve the bearing capacity behaviour of shallow foundations has proven to be a cost effective foundation system. In marginal ground conditions, geosynthetic reinforcement enhances the ability to use shallow foundations in lieu of most expensive deep foundations. There are many situations where foundations are built on slopes or near the edges of slopes such as buildings in hilly regions and foundations for bridge abutments. At many sites, where availability of the land is a problem, construction of embankments with steep slopes is very significant. Steepened slopes can reduce the cost up to 50% as compared to retaining walls. However, the bearing capacity of a foundation constructed near the edge of slope reduces as compared to the foundation constructed on a horizontal ground surface. The improvement of load carrying capacity of such slopes is therefore one of the very important aspects of geotechnical engineering practice as such structures are liable to be unsafe due to slope failure. One of the possible solutions to improve the bearing capacity is to reinforce the sloped fill with the layers of geosynthetic reinforcement. To design a footing on a reinforced sloped fill requires a thorough understanding of both the bearing capacity behaviour of the footing and mechanical behaviour of the reinforced slope. In the present study a numerical analysis of soil slope loaded with rigid strip footing has been carried out using finite element program PLAXIS to find the efficiency of a single layer of reinforcement in improving the bearing capacity of the footing. Data of the

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experimental investigations reported by Mittal, Shah and Verma, (2009) and Choudhary, Jha and Gill, (2010) was used in the numerical analysis.

NUMERICAL ANALYSIS A series of two dimensional FEM analyses was performed for numerical analysis on unreinforced and reinforced slopes using PLAXIS software package (professional version 8, Brinkgreve and Vermeer, 1988). The geometry of the slopes was same as reported in the experimental investigations. Width of footing and angle of slope for a particular case was kept constant. The geometry of finite element model used in the analysis has been shown in Figure 1. The various parameters included in the analysis are listed in table 1.

Bed of testtank

Soil slope

ReinforcementFooting

Side wall of test tank

L

BDe

Z

r

Fig 1: Geometry of finite element model used in analysis

Table 1 Parameters included in numerical analysis

Type of

Soil Test Conditions Slope Angle,

β Width of footing, B

De / B Z / B

Sand Unreinforced 34o 75mm 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0

-----

Reinforced (N=1, SG-150)

2.0, 3.0, 4.0, 5.0 0.25, 0.5, 0.75, 1.0, 1.5, 2.0

Reinforced (N=1, CE-121)

2.0 0.25, 0.5, 0.75, 1.0, 1.5, 2.0

Silty Soil

Unreinforced 45o 100mm 1.0, 2.0, 3.0 -----

Reinforced (N=1)

Polypropylene Model Geogrid

1.0 0.25, 0.5, 0.75, 1.0, 1.5, 2.0, 2.5, 3.0

1.0, 2.0, 3.0 1.0

• Soil Modelling

A variety of soil models are built in the software, however it was decided to use the non-linear Mohr– Coulomb criteria to model the soil due to its simplicity. Parameters involved in this model are Young’s Modulus of Elasticity E, Poisson’s Ratio ν, Cohesion c, Friction Angle φ and

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Dilatancy angle ψ. The soil parameters adopted for a particular soil were assumed to remain the same in all the finite element analyses for the unreinforced system. For the reinforced case, a reinforcement layer was introduced at the required depth with appropriate strength reduction factor between reinforcement and soil and stiffness of the reinforcement was entered as additional parameter. The interaction between the geogrid and soil was modeled at both sides by means of interface elements, which enabled for the specification of a decreased wall friction compared to the friction of the soil. The left vertical boundary of the model was constrained horizontally and the bottom horizontal boundary was constrained in both the horizontal and vertical directions. The soil properties which are included in the finite element analysis are listed in Table 2.

Table 2 Material properties used in numerical analysis

Parameter Sand Silty Soil SG-150 CE-121 Model Geogrid Type of material behaviour Drained Drained Dry unit weight (kN/m3) 16.30 13.82 Saturated unit weight (kN/m3) 18.00 16.00 Modulus of elasticity, E (kN/m2) 7000 4000 Angle of internal friction(φ) 38o 14o Cohesion, c (kPa) 1 20 Angle of dilatancy, (ψ) 10o 0o Poisson’s ratio 0.3 0.38 Strength reduction factor Rinter 0.9(SG-150),

0.75(CE-121) 0.8

Axial Stiffness of geogrid, EA (kN/m)

27.4 6.8 4.0

RESULTS OF NUMERICAL ANALYSIS

Output results of the finite element analyses are shown in figures 2–4. Figure 2 shows the deformed mesh for unreinforced silty soil slope. Figure 3 shows the deformed mesh of the reinforced silty soil slope with edge distance ratio 1.0 and embedment ratio 1.0 and figure 4 shows the deformed mesh for reinforced sand slope for edge distance ratio 2.0 and embedment ratio 0.5.

Fig 2: Deformed mesh for unreinforced silty soil slope

The improvement in load carrying capacity was reported by a non-dimensional factor called ultimate bearing capacity ratio (UBCR), defined as ratio of ultimate load carrying capacity of footing with reinforced slope to the ultimate load carrying capacity of footing without reinforcement.

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Fig 3: Deformed mesh for silty soil slope with very fine element distribution (Z/B= 1, De/B = 1.0)

Fig 4: Deformed mesh for sand slope with coarse element distribution (De/B = 2.0, Z/B = 0.5)

• Analysis of Silty Soil Slopes

Figure 5 shows the comparison of pressure-settlement ratio curves reported in experimental investigation by Choudhary, Jha and Gill, (2010) and those obtained in the numerical analysis for different values of embedment ratio (Z/B). The results of the numerical analysis were found to be in close agreement with the results reported in experimental investigation.

Figure 5. Experimental versus Analytical Pressure-Settlement Ratio Curves (De/B =1.0)

• Effect of Reinforcement Embedment Depth

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In the analysis of silty soil slope, the effect of embedment ratio (Z/B) of single layer of geogrid reinforcement on UBCR was studied by placing it within the soil fill at different depths from the top surface. The edge distance was kept constant i.e. De/B = 1.0. The maximum value of UBCR obtained for silty soil slope is at Z/B= 0.75 to1.0 as reported by Kaur, Gill and Jha (2012).

• Effect of Edge Distance of Footing

The effect of edge distance ratio on the ultimate bearing capacity of unreinforced as well as reinforced slopes was studied. To analyse the effect of edge distance ratio (De/B) on the UBC of reinforced slopes, the footing was placed at three different edge distances with a constant embedment depth of the reinforcement layer (Z/B=1.0). Figure 6 shows the comparison between the trends of variation of UBC obtained from experimental and analytical results at various edge distance ratios both for unreinforced and reinforced slopes.

Fig 6. Variation of Ultimate Bearing Capacity of Unreinforced and Reinforced Slopes with Edge Distance Ratio

It is clear from the figure that the ultimate bearing capacity of the silty soil slopes increases

with increase in the edge distance of the footing. However the effect of reinforcement is maximum when the edge distance is equal to the width of footing. Figure 7 shows the comparison of analytical and experimental bearing capacity for different edge distance ratios (De/B = 1, 2 and 3) and most fitted line. It is clear from the figure that results obtained from numerical analysis are in close agreement with the experimental data.

• Analysis of Sand Slopes

In the analysis of sand slope, the effect of embedment ratio (Z/B) on ultimate bearing capacity of reinforced slopes and effect of edge distance ratio (De/B) on ultimate bearing capacity of reinforced and unreinforced slopes was studied.

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Fig 7. Comparison of Analytical and Experimental Bearing Capacity

• Effect of Edge Distance of Footing

To study the effect of variation of edge distance of footing, both the reinforced and unreinforced slopes were analysed for four different edge distance ratios i.e. De/B = 2.0, 3.0, 4.0 and 5.0. The results indicate that for both reinforced and unreinforced slopes ultimate bearing capacity increases with increasing edge distance. However from the trends of the charts of UBCR versus edge distance ratio showed that the beneficial effect of reinforcement decreases with increase in edge distance. The maximum improvement in the bearing capacity of the sand slope was reported by Kaur, Gill and Jha (2012) for De/B = 2.0.

• Effect of Reinforcement Embedment Depth

To study the effect of embedment ratio on bearing capacity of footing, slope was analysed for Geogrid SG-150 placed at six different embedment depths i.e. 0.25B, 0.5B, 0.75B, 1.0B, 1.5B, 2.0B for each case of edge distance ratio. The geogrid CE-121 was also placed at all the mentioned embedment depths for edge distance ratio 2.0. The optimum value of embedment ratio (Z/B) for all the cases was found to be 0.5 as reported by Gill, Kaur, Chaudhary and Jha (2011). Figure 8 shows the variation of ultimate bearing capacity with embedment ratio as obtained in present analysis and that reported by Lee and Manjunath (2000) in their experimental investigations. In both the cases same geogrid CE121 was used. However the other parameters such as slope geometry, edge distance ratio and properties of sand were different. It is clear from the figure that results obtained in both the studies show similar trends which indicate that the

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benefit of a reinforced slope gains its peak when the reinforcement embedment depth is equal to 0.5 times width of footing.

Fig 8. Comparison between trends of variation of UBCR with Z/B ratio obtained in present analysis and analysis by Lee Manjunath (Geogrid CE-121)

On the two sides of this critical Z/B ratio, the efficiency of the reinforcement decreases significantly as indicated by the reduction of UBCR values. When Z/B = 2.0, the performance of the reinforced slope becomes rather minimum as value of UBCR approaches towards unity. According to Lee and Manjunath (2000), this behaviour can be explained by the “deep footing effect” as suggested by Huang et al. (1994). When the restraining force exerted by reinforcement is imposed on soil elements, the reorientation of the strain characteristics associated with the restraint of minor principal strain of the soil elements occurs in the vicinity of the reinforcement. A part of the reinforced zone where relatively large reinforcement force has developed behaves like a part of the rigid footing and transfers a major part of the footing load into a deeper zone. This load-transfer mechanism seems to reach the optimum when the reinforcement embedment depth to footing width ratio Z/B is about 0.5. At larger depths of embedment, the contribution to the load transfer mechanism caused by the presence of the reinforcement reduces significantly. For higher values of embedment ratio, the system behaves more or less like an unreinforced slope. This explanation seems to be consistent with the experimental results of Selvadurai and Gnanendran (1989) and Huang et al.

CONCLUSIONS A numerical study was carried out on rigid strip footing resting on unreinforced and reinforced earth slopes. The study primarily aimed at determining the effect of geogrid reinforcements and its location on the ultimate bearing capacity of such footings. Based on this study, the following conclusions are made:

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• The provision of a reinforcement layer at an appropriate location in slopes results in a significant increase in the bearing capacity of footings.

• The optimum depth of location of the single geogrid layer for silty soil is at a depth of 0.75 to 1.0 times the footing width. However, the optimum depth of location of the single geogrid layer for sand slope is at a depth of 0.5 times the footing width.

• The load carrying capacity of footing increases with increase in edge distance. However ultimate bearing capacity ratio decreases with increase in edge distance ratio for both silty soil slopes and sand slopes.

• A good agreement between the experimental and numerical results on general trend of behaviour and the critical values of the reinforcement parameters is observed.

References

Choudhary, A.K.; Jha, J.N.; Gill, K.S.; (2010); Laboratory investigation of bearing capacity behavior of strip footing on reinforced flyash slope; Geotextiles and Geomembranes; 28(4); 393-402.

Gill, K.S.; Kaur, A.; Choudhary, A.K.; Jha, J.N. (2011); Numerical study of footing on single layer reinforced slope; Proceedings of Indian Geotechnical Conference; (2); 839-842.

Huang, C.; Tatsuoka, F.; Sato, Y.; (1994); Failure mechanism of reinforced sand slopes loaded with footing; Soil and Foundation; 24(2); 27-40.

Kaur, A.; Gill, K.S.; Jha, J.N. (2012); Numerical study of geosynthetic-reinforced earth slopes loaded with strip footing; Proceedings of Innovative Challenges in Civil Engineering, PTU Giani Zail Singh Campus; 86-91.

Lee, K.M; Manjunath, V.R.; (2000); Experimental and numerical studies of geosynthetic reinforced sand slopes loaded with footing; Canadian Geotechnical Journal; 37; 828-842.

Mittal, S.; Shah, M.Y.; Verma, N.K; (2009); Experimental study of footing on reinforced earth slope; International Journal of Geotechnical Engineering; 3(2); 251- 260.

Selvadurai, A.; Gnanendran C; (1989); An experimental study of a footing located on a sloped fill : influence of a soil reinforcement layer; Canadian Geotechnical Journal; 26(3); 467-473.

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COMPUTATIONAL MODELLING OF SOIL NAIL WALLS: A CASE STUDY

V.P. Singh Civil Engineering Department, Thapar University, Patiala, India

Abstract: Soil nailing is being used extensively in many geotechnical applications to improve stability of excavated vertical cuts and existing natural slopes. This paper presents a soil nail wall case study wherein the stability of supported vertical cut was examined using a finite element based computational tool.

INTRODUCTION Soil nailing consists of reinforcing the ground by closely spaced passive inclusions to create in-situ a coherent gravity structure, and thereby, increasing the shear strength of the in-situ soil and restrain its displacements. The basic design consists of transferring the resisting tensile forces generated in the inclusions into the ground through the friction mobilized at the interfaces. In a soil nail wall, the properties and material behavior of three components - the native soil, the nails and the facing element and their mutual interactions significantly affect the performance of the structure. In addition, various factors such as the construction sequence, the installation of nails, the connection between the nails and the facing are likely to influence the behavior. Owing to such a complex soil-structure interaction, it is diffcult to assess stability and performance of soil nail walls using conventional closed form methods. Consequently, computational modelling can provide a much better insight into the overall behavior of soil-nail walls. A significant literature including Briaud & Lim (1997), Babu et al. (2002), Murthy et al. (2002), Fan & Luo (2008) and Singh & Babu (2010) is available on computational modelling of soil nail walls.

DESIGN METHODS AND GENERAL SPECIFICATIONS Since its inception, various approaches such as limit equilibrium analysis, multi-criteria analysis, kinematical limit analysis, strain compatibility analysis, discrete element analysis, nonlinear programming and finite element analysis are developed to study behaviour of soil nail walls. However, it is noteworthy that the limit equilibrium based methods have attracted the attention of the researchers because of their simplicity, reasonable accuracy and popularity among the practicing engineers. The main shortcoming of limit equilibrium based methods is that they fail to account for deformation behaviour of soil nail walls adequately. Estimates of deformation could be obtained using numerical techniques (e.g. finite element and finite difference methods). A detailed discussion on various analysis and design philosophies for soil nail walls could be found elsewhere, however, general steps involved in the design of soil nail walls according to most widely used manual (FHWA 2003) for soil nail wall analysis and design are as follows:

• For the specified structure geometry (depth and cut slope inclination), ground profile, and boundary (surcharge) loadings, working nail forces are estimated and location of the potential sliding surface are determined.

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• Selection of the reinforcement type (type, cross-sectional area, length, inclination, and spacing) is done and verification of local stability at each reinforcement level is assured.

• Verification of global stability of the nail-soil structure and whether the surrounding ground is maintained during and after excavation with an acceptable factor of safety is carried out.

• Estimation of the system of forces acting on the facing (i.e., lateral earth pressure and nail forces at the connection) and hence, design of the facing for specified architectural and durability criteria is to be carried out.

According to FHWA (2003) some the general guidelines for preliminary design of soil nail

wall are presented in Table 1.

Table 1: Recommended guidelines for soil nail wall preliminary design

Item Recommended Guideline Nail installation process Drilled and Grouted / Driven

Nail spacing Grouted nails: 1.25 m to 2 m; Driven nails: 0.5 m to 1.20 m (Influence area : SH x SV ≤ 4m2)

Nail diameter Grouted nails: 100 – 200 mm drillhole diameter for grouted nails with minimum 20 mm reinforcement bar. Driven nails: 20 mm to 36 mm reinforcement bar

Nail length 0.7 to 1.0 times the vertical wall height Nail inclination (wrt horizontal) 10 to 20 degrees (usually 15 degrees) Nail pattern at wall face Square or staggered Yield strength of reinforcement bar ≥ 415 MPa Compressive strength of grout / shotcrete ≥ 20 MPa

Minimum cover to reinforcement for corrosion protection 25 mm (minimum)

Temporary facing thickness 75 mm – 100 mm (shotcreted welded wire mesh)

Permanent facing thickness 150 mm – 200 mm (cast-in-place reinforced concrete or precast concrete facing)

Wall face batter (wrt vertical) 0 to 10 degrees

FAILURE MODES OF SOIL NAIL WALLS A design for soil nail wall must ensure that it is safe against its various failure modes. Failure modes of soil nail walls are broadly classified into three distinct groups as: external failure modes, internal failure modes and facing failure modes (FHWA 2003). Various failure modes of soil nail walls are shown in Figure 1. A brief discussion on these broad classifications of failure modes of soil nail walls is presented below.

• External Failure Modes

Global stability and sliding stability are the two prominent external failure modes of soil nail walls. Global stability refers to the overall stability of the reinforced soil nail wall mass. In this failure mode, along the slip surface the driving force due the self weight and external loading on the retained mass exceeds the resisting force provided by the in-situ soil and the nails. On the other

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hand, sliding stability considers the ability of the soil nail wall to resist sliding along the base of the retained system in response to lateral earth pressures behind the soil nails. Sliding failure may occur when additional lateral earth pressures, mobilised by the excavation, exceed the sliding resistance along the base. Since, the wall facing does not extend below the bottom of the excavation, the unbalanced load due to the excavation may cause the bottom the excavation to heave and stimulate a bearing capacity failure of the foundation. Usually, a factor of safety in the range 1.35-1.50 is recommended for external failure modes.

Fig 1: Principal Failure Modes of Soil Nail Walls

• Internal Failure Modes

Pullout failure and tensile failure of soil nails constitutes the two most prominent internal failure modes. Nail pullout failure is a failure along the soil-grout or soil-nail interface due to insufficient intrinsic bond strength and / or insufficient nail length. Tensile failure of a soil nail takes place when the maximum tensile axial force in the soil nail is greater than the nail tensile capacity. The other possible internal failure modes of soil nail walls are nail bending and / or shear failure. However, it is reported in literature (Elias & Juran 1991) that the shear and bending resistances of the soil nails are mobilised only after occurrence of relatively large displacements along the slip surface. Elias & Juran (1991) concluded that shear and bending nail strengths contribute less than 10 percent to the overall stability of the soil nail wall and therefore, failure of soil nails due bending and / or shear can be ignored. Usually, a factor of safety in the range 1.8-2.0 is recommended for internal failure modes.

• Facing Failure Modes

Facing flexure failure and facing punching shear failure are the two prominent facing failure modes of the soil nail walls. Facing flexure failure occurs due to the excessive bending beyond the facing’s flexural capacity, whereas, facing punching failure occurs due insufficient shear capacity of the facing element around the nail head. Design of facing for soil nail walls is based on the

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maximum axial force expected at the nail head. Facing failure modes are generally governed by the construction method employed.

CASE STUDY: MODELLING OF SOIL NAIL WALL The primary objective of this study was to emphasize on the feasibility of soil nail wall as an effective technique of stabilization of vertical cuts. A soil nail wall was designed conventionally based on the Federal Highway Administration (FHWA 2003) guidelines. An extensive geotechnical investigation was carried out to assess in-situ soil conditions. The entire soil-nail wall system was then modelled using a finite element program (Plaxis 2006). Various design variables were studied and compared. In particular, emphasis is laid on the effect of nailing on deformations and global factor of safety. The properties of the native soil and the reinforcement are given in Table 2.

Table 2: Properties of the native soil and the reinforcement

Parameter Symbol Unit Value

Wall Layout

Vertical height H m 6.80

Face batter α Degrees 0.0

Slope of backfill β Degrees 0.0

Soil Properties

Cohesion c kPa 10 - 20

Friction angle φ Degrees 25

Unit weight γ kN/m3 18

Modulus of elasticity ES MPa 20

Poisson’s ratio ν -- 0.3

Driven Nail and Facing Properties

Length LN m 3.50

Diameter D m 0.02

Spacing SV x SH m x m 0.5 x 0.5

Modulus of elasticity EN N/m2 2 x 1011

Soil-nail interface friction φu Degrees 25 Thickness t m 0.1 Modulus of elasticity EC N/m2 2 x 1010

CONSTRUCTION STAGES AND MODELLING

The construction procedure consisted of excavation, installation of the reinforcement (i.e. nails), and construction of RCC facing. First, the soil was excavated to a depth of 1500 mm, and nails were driven at the desired spacing in both the horizontal and vertical directions. Nominal reinforcement for the RCC facing was provided and rigidly connected to the nails by welding. Subsequently, a 100 mm thick RCC facing was constructed. The process was repeated until the desired depth of excavation was reached.

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As mentioned earlier, for the computational modelling, two-dimensional finite element program Plaxis was used. Mohr-Coulomb model was used to model soil, and for nails and facing elements an elastic model is used. Beam elements were used to model nails and facing elements. Input parameter definitions in Plaxis take care of averaging the effect of a three-dimensional problem to a two-dimensional problem. Figure 2 shows the modelled state of the soil nail wall.

Accomplishment of physical modelling, including simulation for gravity stresses using K0-procedure, was followed with the calculation program. Simulation of the entire soil-nail wall construction process was carried out in a sequence of construction stages. In each construction stage a sufficient number of calculation steps were used to obtain an equilibrium-state. Since the properties of the soil at the location are highly variable, the representative values of soil cohesion 10, 15 and 20 kPa were used for numerical analysis. Factor of safety and displacements were noted after each construction stage.

Fig 2: Finite Element Model for the Soil-Nail Wall

RESULTS AND DISCUSSIONS Strength reduction technique (Matsui and San, 1992) is used for the calculation of factor of safety. The advantage of this method is the identification of critical failure mechanism automatically, which is normally assumed in the conventional analysis. Dawson et. al, (1999) showed that the factors of safety calculated from this approach are very close to the values obtained from conventional methods in geotechnical analysis. They also indicated that this method is more general and flexible and it is more advantageous particularly when the failure mechanism is complex.

• Global Factor of Safety

Global factor of safety was obtained using strength reduction technique after each construction stage. Three sets of observations corresponding to cohesion value of 10 kPa, 15 kPa and 20 kPa were obtained and the improvement in factor of safety is observed. Table 3 indicates the obtained factors of safety. An improvement of about 1.5 – 2.5 times in values of factor of

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safety is observed. Also, it could be noticed that a global factor of safety in the range of 1.20 – 1.53 is obtained for the entire depth (6.8 m) of excavation supported using nails.

Table 3: Factors of safety obtained using strength reduction technique

Construction Depth (in m)

Factor of Safety Without Nailing With Nails

Cohesion, c (kPa) 10 15 20 10 15 20 1.50 1.32 1.87 3.29 3.40 4.48 5.17 3.00 -- 1.06 1.18 2.03 2.43 2.86 4.50 -- -- 0.96 1.62 1.87 2.18 6.00 -- -- -- 1.28 1.51 1.72 6.80 -- -- -- 1.20 1.37 1.53

• Lateral (Horizontal) Deformations

Table 4 shows the horizontal displacements at different construction stages. It could be noticed that a maximum horizontal deformation of 7.60 mm was observed for the nailed wall, contrary to that of 27.25 mm for excavation of 6 m without nailing. It is a significant reduction (about 70%) in the displacement of the vertical cut. Figure 3 show the results of numerical simulation for variation of percent wall displacement (computed with respect to the wall height in current construction stage). From Figure 3, maximum wall displacements are evident during initial 40-50% of the full construction and reduce significantly thereafter. For the fully constructed wall, maximum displacement is found to be nearly equal to the permissible deformations (Juran 1985) of 0.2% of vertical height of wall.

Table 4: Horizontal displacements with construction stages

Construction Depth (in m)

Extreme Horizontal Displacement (in mm) Without Nails With Nails

Cohesion, c (kPa) Cohesion, c (kPa) 10 15 20 10 15 20

1.5 1.20 1.20 1.21 1.24 1.25 1.25 3.0 3.45 2.04 1.86 2.23 1.67 1.66 4.5 -- 7.33 6.03 5.20 3.83 3.48 6.0 -- -- 27.25 11.23 9.05 7.60 6.8 -- -- -- 16.17 12.55 11.00

Fig 3: Variation of Horizontal Displacements with Construction stages

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• Stress Parameters

A soil nail walls consists of structural elements such reinforcement bars representing “nails” and facing elements made up of shotcrete and/or reinforced concrete. The restraining action of the soil nail wall results in the development of stress parameters such as axial forces, shear forces and bending moments both in nails as well as facing elements. A variation of these stress parameters can be obtained from the computational analysis. As an example, Figure 4 shows axial force variation along the nail length for various nails installed at different depths. From Figure 4, it can be seen that maximum axial force occurs in the bottommost nail and also the position of maximum axial force shifts towards facing with depth of embedment. Further, an imaginary line joining the points of maximum axial forces in different nails represents a possible failure surface. Similarly, variation of other stress parameters can be studied.

Fig 4: Variation of Axial Force in Nails Installed at Different Depths

CONCLUDING REMARKS In this paper, an attempt is made to present preliminary information about soil nailing technique. Further, in context of a case study, the advantages of using computational modelling to study stability and performance of soil nail walls is illustrated. The results of the modelling indicated that the soil nail wall was efficient enough to support most vulnerable slope i.e. vertical cut. Further, it can be concluded that a rigorous computational modelling with proper boundary conditions, mesh densities, exhaustive material parameters and use of appropriate material models, can account for the complex soil-structure interaction and provide a realistic analysis of soil nail walls.

ACKNOWLEDGEMENT

Sincere thanks are expressed to Prof. GL Sivakumar Babu, IISc Bangalore, for his guidance in developing author understands of soil nail technique. References Babu, G.L.S., Murthy, B.R.S. and Srinivas, A. (2002). Analysis of construction factors influencing the

behavior of soil nailed earth retaining walls, Groun. Improve., 6(3), 137-143. Briaud, J.L. and Lim, Y. (1997). Soil-nailed wall under piled bridge abutment: simulation and

guidelines, J. of Geotech. Geoenviron. Engg., ASCE, 123(11), 1043-1050.

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Dawson, E.M., Roth, W.H.A. and Drescher, A. (1999). Slope stability analysis by strength reduction, Geotechnique, 49(6), 835-840.

Elias, V. and Juran, I. (1991). Soil nailing for stabilization of highway slopes and excavations, Federal Highway Administration, Washington, Report FHWA-RD-89-198.

Fan, C.C. and Luo, J.H. (2008). Numerical study on the optimum layout of soil nailed slopes, Comput. Geotech., 35(4), 585-599.

FHWA (2003). Geotechnical engineering circular No. 7 - soil nail walls, Federal Highway Administration, Washington, Report FHWA0-IF 03-017.

Juran, I. (1985). Reinforced soil systems - application in retaining structures, Geotech. Engg., 16(1), 39-81.

Matsui, T. and San, K.C. (1992). Finite element slope stability analysis by shear strength reduction technique, Soils and Found., 32(1), 59-70.

Murthy, B.R.S., Babu, G.L.S. and Srinivas, A. (2002). Analysis of prototype soil nailed retaining wall, Groun. Improve., 6(3), 129-136.

Plaxis (2006). Reference manual, Delft University of Technology & Plaxis B.V., The Netherlands. Singh, V.P. and Babu, G.L.S. (2010). 2D Numerical simulations of soil nail walls, Geotech. Geolog.

Engg., 28(4), 299-309.

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MULTILAYER REINFORCED COAL ASH SLOPE: EXPERIMENTAL INVESTIGATIONS

Gurdeep Singh, K. S. Gill and J. N. Jha Department of Civil Engineering, Guru Nanak Dev Engineering College, Ludhiana, India.

Abstract: In the present experimental investigation attempt has been made to study the bearing capacity and settlement characteristics of strip footing subjected to central vertical load, resting on reinforced coal ash slope with the help of model test for multilayer reinforced and unreinforced cases. Laboratory tests were conducted by varying parameters such as the distance of footing from the edge of slope at crest, embedment ratio and number of reinforcement layers. Slope angle and footing width were kept constant. Coal ash being a waste product possess large disposal problem, so it is commonly used in various civil engineering projects. Coal ash being non-plastic, light in weight & having high compaction level proves to be advantageous material for slope preparation over coarse granular soils. Detailed results along with graphs and conclusion have been covered which will provide complete understanding of the research work. Future scope gives an idea about more investigation on this topic. The results of the investigation indicates that both the pressure-settlement behaviour and the ultimate bearing capacity of footing resting on the top of a coal ash slope can be enhanced by the presence of reinforcing layers. The results were found to be encouraging.

INTRODUCTION

Reinforced slopes are cost-effective alternatives for construction where the cost of fill, right-of-way, and other considerations may make a steeper slope desirable. Where the soil or ground is not inherently stable it will be prone to failure, so the performance of the existing soils needs to be improved. There are many ways to achieve, but increasingly geogrids are used to reinforce the soils within embankments or slopes. Soils are good in compression and poor in tension. Geogrid reinforcement is good in tension and poor in compression. A composite of these materials offers the benefits of both geogrid reinforcement used in conjunction with the soil enable that soil to perform better than it would in its unreinforced state, accommodating greater loads or standing at steeper angles. Unsurpassed range of geogrid reinforcements maximizes the opportunity to reuse site won materials as backfill to a reinforced slope. This saves on the export and import of materials from site, embracing sustainability and reducing polluting truck movements. Use of coal ash, which is a waste material left after burning of coal in thermal power plants is a better & cost-effective solution to construct a stable slope. Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata of coal mines in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure. This coal is then transported through railways over long distances to thermal power plants. The waste material left after the burning of coal in thermal power plants is called as “Coal ash”. The high temperature of burning coal turns the clay minerals present in the coal powder into fused fine particles mainly comprising aluminium silicate. Coal ash produced thus possesses both ceramic and pozzolanic properties. Coal ash when used in structural fills or embankments offers several advantages over borrow soils. It is light in weight compacted embankment made of coal ash would exert only 50 % of the pressure on a soft subgrade as a fill of equivalent height using coarse granular borrow and again

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the compaction curve of coal ash is relatively flat thus implying that construction is less sensitive to compaction-moisture content than that of the fine grained soils commonly used as structural fill. Coal ash being non-plastic will also solve the problem of dimensional instability as exhibited by plastic soils. Coal ash is further categorised as:

1. Fly ash: Fly ash is the finest of coal ash particles. It is called "fly" ash because it is transported from the combustion chamber by exhaust gases. The combustion of powdered coal in thermal power plants produces fly ash.

2. Bottom ash: Bottom ash is a coarse, granular, incombustible byproduct that does not rises up along with exhaust gases and is collected from the bottom of furnaces. Bottom ash is coarser than fly ash, with grain sizes spanning from fine sand to fine gravel.

3. Pond ash: Boiler slag and bottom ash are mixed together with water to form slurry, which is pumped to the ash pond area as shown in Fig.No.2. In ash pond area, ash gets settled and excess water is decanted. This deposited ash is called pond ash.

When pulverized coal is burnt to generate heat, the residue contains 80 percent fly ash and 20 percent bottom ash. The ash is carried away by flue gas collected at economizer, air pre-heater and ESP hoppers. Clinker type ash collected in the water-impounded hopper below the boilers is called bottom ash. The World Bank has cautioned India that by 2015, disposal of coal ash would require 1000 square kilometers or one square metre of land per person. Nearly 73% of India's total installed power generation capacity is thermal, 90% of it is coal-based.India has about 70 thermal power plants and 70 per cent of them burn coal to generate power. Various Indian collieries supply the coal, which is known to have a very high ash content of almost 40 to 45 per cent. India's thermal power plants produce an estimated 100 million tonnes of coal ash per annum. Of this, RTPS (Raichur Thermal Power Station) alone generates about 1.5 million tonnes at 4,000 tonnes daily. Out of this, 80 per cent is fly ash and 20 per cent bottom ash. This ash needs to be disposed of every day. Several factors have impeded coal ash utilization in India, while it is being extensively used globally. Coal-based thermal power stations have been operational for more than 50 years but the concept of developing environment friendly solutions for coal ash utilization is only about 15 years old. Overall coal ash utilization in India stands at a fairly low level of about 15 per cent of the quantity generated.

In the present experimental investigation attempt has been made to study the bearing capacity and settlement characteristics strip footing subjected to central vertical load, resting on reinforced coal ash slope with the help of model test. For this, tests in plain strain condition on a 2000 mm x 300 mm x 65 mm size footing on unreinforced and multilayer reinforced slopes were performed for central vertical load. Tests are planned for Geogrid (SGi-040). The tests were conducted by varying the distance of footing to the edge of slope at top surface, embedment ratio and number of reinforcement layers. The results obtained from model tests have been verified by available literature.

EXPERIMENTAL INVESTIGATION

• Materials

Coal ash used in the study was Pond ash, collected from “Guru Gobind Singh Super Thermal Plant, Ropar. The maximum dry density and the corresponding optimum moisture content (OMC) were 11.01 kN/m3 and 27.4% respectively. Commercially available Geogrid (SGi-040) 0.27 mm thick with 60 mm x 23 mm aperture size wide having single rib tensile strength of 33.9 kN/m in CD & 43.4 kN/m in MD was used as reinforcing elements.

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• Test Tank

A rectangular steel tank of size 4650 mm x 2000 mm x 1500 mm was used in the model test. The sides of the tank were covered by thin polythene sheet and a coating of white grease was applied on the polythene sheet to minimize the frictional resistance. To eliminate the lateral deflection under axial load on the footing the longitudinal side walls of the test tank were strengthened by means of metallic stiffeners. The tank sides were rigidly welded with the vertical posts which were tightly fastened to the foundation base. A horizontal cross beam was fixed on the vertical posts to support the loading device across the middle of the tank.

• Model Footing

A strip footing of seasoned sal wood of size 2000 mm x 300 mm and having a thickness of 65 mm was used. The length of the footing was made almost equal to the width of the tank in order to maintain plain strain conditions. The two ends of the footing were polished smooth to minimize the end friction effects. The base of the footing was made rough, to simulate the roughness of actual footing. The load was applied centrally on the footing to avoid tilting of the footing. The load was applied at the centre on the footing through the plunger of hydraulic actuator.

• Preparation of Slope

Roller compaction was used for the preparation of slope. Slope was prepared with dimensions 3200 mm x 2000 mm x 1000 mm inside the test tank having dimensions 4650 mm x 2000 mm x 1500 mm. The pond ash which was transported from Guru Gobind Singh Super Thermal Plant, Ropar was wet enough having moisture content 22 percent. This moisture content was sufficient enough to achieve the 95 percent dry density after compaction in the test tank. Well mixed pond ash was then spread into the tank in five equal layers each 250 mm thick. In order to ensure uniform compaction of each layer a 116 kg smooth towed roller was passed 20(predetermined) times over each pond ash layer so as to attain a final compacted layer of 200 mm thickness. Before placing the next layer, the earlier layer was scratched with sharp edge in order to provide adequate bonding between the consecutive layer and procedure was repeated until the desired height of 1000 mm was reached. For the control of in-situ density before final compaction, few trials of compaction were carried out by varying passes of 116 kg roller & determining in-situ density after each trial of specified no. of passes. After each trial of specified no. of passes, no. of passes were increased & dry density was again determined. Dry density was determined by placing a mould of known volume inside layer of pond ash. After compaction, weight of mould along with compacted ash was known & bulk density was determined. Then dry density was final calculated. This process was repeated till the placement dry density achieved by this procedure was 95% of the standard proctor density. Same procedure was followed for both unreinforced & reinforced cases. Only difference in reinforced case was that after compaction, reinforcement layer was placed at different z/B ratio.

• Loading Arrangement

Fig.No.1 shows the loading arrangement of the experimental set up

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Fig.1: Loading arrangement of the experimental set up 1. Data Taker instrument 7. LVDT-1 2. Laptop 8. LVDT-2 3. Loading Frame 9.Model Footing (Wooden) 4. Hydraulic Actuator 10. Ash Slope 5. Loading Cell 11. Compacted Ash Model 6. Cylindrical Loading Piece 12. Connecting Wires

EXPERIMENTAL PROCEDURE

After the preparation of the slope in case of unreinforced or multilayer reinforced case, model footing was placed at specified edge distances (De = 1B, 2B or 3B). Now loading arrangement was done, connections with data taker were done & load cell was placed over the top cylindrical loading piece. Piston of the jack was lowered to a level where sufficient space remains available between the load cell & the plunger of jack. The loading beam and Jack were placed into the position at the center of footing . While placing the model footing sufficient care was taken to ensure that the model was placed horizontal so that the load is always applied vertical. The two LVDT’s with their stands were fitted at the two corners of the footing to measure the settlement of the footing during the of application of the load. The plunger was lowered and the desired seating load was applied. The initial reading of the loading gauge and LVDT’s were recorded. Loads are applied in equal increments only when the settlement was reasonably constant. Before each increment of the load, the readings of the loading gauge and LVDT’s were recorded. The procedure was continued upto failure. From the observations of the test, finally a load-settlement curve was drawn and the ultimate bearing capacity of the footing was obtained by using double

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tangent method. Same procedure was repeated for different number of reinforcement layers (N = 2, 3 or 4) for multilayer cases at different z/B ratio ( 0.25, 0.50, 0.75 or1).

• Test Parameters

Parameters such as slope angle (β), footing width (B) and vertical spacing between reinforcement layers (Sv=7.5 cm) were kept constant. Variable parameters were distance of footing from edge of slope at crest (De), embedment ratio (z/B) & number of reinforcement layers (N). Total number of 21 tests were performed. Out of which 3 tests were for unreinforced case & 18 tests were for multiple layered reinforced case. The following are the parameters studied in model tests & are shown in Table.No.1.

Table 1: Parameters of test programme

S No.

Type of test

Constant Parameters

Variable Parameters

1. Unreinforced slope B = 300 mm, β = 45o

De/B = 1, 2, 3

2. Reinforced slope mutiple layer (N = 2)

B = 300 mm, β = 45o

z/B = 0.25,0.50 De/B = 1, 2, 3

2(a). Reinforced slope

mutiple layer (N = 2)

B = 300 mm, β = 45o

z/B = 0.50,0.75 De/B = 1, 2, 3

2(b). Reinforced slope

mutiple layer (N = 2)

B = 300 mm, β = 45o z/B = 0.75,1.0

De/B = 1, 2, 3

3. Reinforced slope mutiple layer (N = 3)

B = 300 mm, β = 45o

z/B = 0.25,0.50,0.75 De/B = 1, 2, 3

3(a). Reinforced slope

mutiple layer (N = 3)

B = 300 mm, β = 45o

z/B = 0.50,0.75,1.0 De/B = 1, 2, 3

4. Reinforced slope mutiple layer (N = 4)

B = 300 mm, β = 45o

z/B= 0.25,0.50, 0.75,1.0 De/B = 1, 2, 3

RESULTS AND DISCUSSION

• Bearing Capacity Behaviour for multiple number of layers (N = 1, 2, 3, 4)

The increase in bearing capacity of model slope is based on the transference of tension forces from the material (pond ash) to the geogrid layers. The transfer of tension forces from pond ash to the geogrid layers takes place by friction, passive earth resistance and interlock effect. So increase of geogrid layers increases the effect of factors governing the transfer of tension forces which further increases the bearing capacity of the slope.So maximum bearing capacity was achieved in case of N = 4 as shown in Fig 2. Bearing capacity ratio (BCR) results shown Fig 3 also concludes that BCR becomes constant after N = 3 and thereafter the increase is only marginal.

• Effect of De/B ratio for multilayer reinforced slope

De/B ratio for multilayer reinforced slope has same effect as in case of unreinforced case. Bearing capacity increases with the increase in De/B ratio. Bearing capacity was maximum at De/B = 3 as shown in Table.No.2. Also it was observed that bearing capacity of a given slope remains almost constant if the edge distance is increased beyond 3B and the footing tends to behave as if it is placed on a level ground. When the footing is placed at sufficient distance away from the slope

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crest the passive resistance from the slope side to failure wedge under the footing increases and thus increasing the bearing capacity load.

Fig. 2: Load-Settlement curves at different number of geogrid layers for De/B = 1

Fig 3: BCR vs number of geogrid layers for different De/B ratios

Table.2: Bearing capacity results for N=2 with different De/B ratio at z/B = 0.25, 0.50

z/B ratio BC for De/B = 1 BC for De/B = 2 BC for De/B = 3

0.25,0.50 80 98 117

• Effect of z/B ratio for multilayer reinforced slope

Table 3 shows that in case of N= 2 bearing capacity of the footing is maximum for z/B = 0.25, 0.50 and minimum for z/B = 0.75, 1. This concludes that lesser the z/B ratio for multilayers of geogrid, more is the bearing capacity & vice versa.When geogrid is placed at lesser z/B ratio as in case of N = 2 & N = 3, bearing capacity increases due to confinement of pond ash between multilayers of geogrid. On the other hand, when z/B ratio is more ,the unreinforced zone directly below the footing becomes thicker and as a result a shear failure of the unreinforced zone is likely, thus decreasing the load-bearing capacity. It would appear that the plane of reinforcement acts as a plane of weakness

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Table.3: Bearing capacity results for N=2 with different z/B ratio & De/B=1,2,3

z/B ratio BC for De/B = 1 BC for De/B = 2 BC for De/B = 3

0.25,0.50 80 98 117

0.50,0.75 76 91 112

0.75,1 70 89 100

CONCLUSIONS

Within the framework of the present investigation, the following conclusions can be drawn.

• Reinforced pond ash slopes are cost-effective alternatives for new construction where good material is not locally available for attaining stable steeper slopes.

• The behaviour of shallow footings on multilayer reinforced pond ash slope were greatly affected by distance of footing from the edge of slope (De/B), embedment ratio (z/B) and no. of reinforcement layers (N).

• The load carrying capacity of the footing resting on top of a pond ash slope is low for unreinforced case but for multilayer reinforced case, there is a improvement in the load carrying capacity of footings located on such slopes.

• The edge distance (De) from the slope crest greatly effects the load carrying capacity of unreinforced as well as multilayer reinforced slopes. Bearing capacity of footing increases with increase in edge distance.

• The load capacity of the footing is maximum for z/B = 0.25, 0.50 and minimum for z/B = 0.75, 1. This concludes that lesser the z/B ratio for 2 layers of geogrid, more is the bearing capacity & vice versa. Similar results are obtained for N = 3.

• The load carrying capacity of footing located on top of a multilayer reinforced pond ash slope increases with increase in number of reinforcing layers for all the edge distances as adopted in the present study. However, the increase is significant up to three number of reinforcing layers (N = 3) and thereafter the increase is only marginal. BCR also shows similar results.

References

Choudhary, A.K; Verma, B.P; (2001); (Behavior of footing on reinforced sloped fill); Proceedings, International Conference on Landmarks in Earth Reinforcement, Japan; 535-539.

Gill, K.S; Choudhary, A.K; Jha, J.N; (2010); (Stability of strip footing on reinforced fly ash slop); Proceeding, 6th International Congress on Environmental Geotechnics, 2; 1160-1165.

Gill, K.S; Choudhary, A.K; Jha, J.N; (2010); (Laboratory investigation of bearing capacity behaviour of strip footing on reinforced fly ash slope); Geotextiles and Geomembranes, 28(4); 393-402.

Gill, K.S; Shukla, S.K; Jha, J.N; Choudhary, A.K; (2011); (Load bearing capacity of footing resting on a multilayer reinforced fly ash slope); Proceedings of Indian Geotechnical Conference, Kochi(paper no. N-055).

Mittal, S; Shah, M.Y; Verma, N.K; (2009); (Experimental study of footing on reinforced earth slope); International Journal of Geotechnical Engineering, 3(2); 251- 260.

Mandal, J.N; Bhardwaj, D.K; (2008); (Study on polypropylene fibre reinforced fly ash slopes); 12th international conference of international association for computer methods and advances in geomechnics, Goa, India; 3, 3778-3786.

Shukla, S.K; Sivakugan, N; Das, B.M; (2011); (A state of the art review of geosynthetic reinforced slopes); International Journal of Geotechnical Engineering; 5(1) , 17-32.

488

STRENGTH BEHAVIOR OF POND ASH CEMENT MIX

Karanbir Singh Randhawa, J.N.Jha and K.S. Gill Department of Civil Engineering, Guru Nanak Dev Engineering College, Ludhiana, India.

Abstract: Due to enormous production of fly ash/pond ash which is as a by-product of coal combustion, thus requiring huge disposal area and creating environmental problems. In India, where land to population ratio is too small, acquiring huge area of land for the disposal of fly ash is not easy. Hence the proper utilization of fly ash without causing problem to environment is a foremost concern. The aim of present study is to carry out different laboratory test on cement stabilized pond ash. Different percentage of cement content was added and the effect of cement content on the strength properties of the mix was ascertained. Synthetic fiber in different percentage was also added for optimum mix only and flexural test was again conducted to see the effect of fiber on flexural strength.

INTRODUCTION

In order to conserve the natural resources and energy, several waste products have been proposed in recent years for use as alternative construction materials. One by product that has shown substantial potential as an alternative construction material is pond ash, if proper and adequate additives are used. Pond ash a solid residue obtained from the ash pond constructed near the thermal power stations. Thermal power plants have been a major source of power generation in India, where 75% of the total power obtained is from coal-based thermal power plants (Senapati 2011). In India about 120 coal based thermal power stations are producing about 112 million tonne fly ash/ pond ash per year. With the increasing demand of power and coal being the major source of energy the ash generation is expected to increase to about 225 million tonne by 2017 (Kumar et al. 2005). Due to enormous production of fly ash/pond ash as a by-product of combustion, it requires huge disposal area and creates environmental problems. In India, where land to population ratio is too small, acquiring huge area of land for the disposal of fly ash is not easy. Hence the proper utilization of fly ash without causing problem to environment is a foremost concern for developing country like India. For many years several researchers contributed their significant research work to convert fly ash in to useful construction material (McLaren and DiGioia 1987; Glogowski et al. 1992; Kaniraj and Havangi 1999, Sridharan et al. 2001; Kaniraj and Gayathri 2003; Das and Yudhbir 2005, Choudhary et al. 2010, Gill et al. 2013). Fly ash can be used in various geotechnical engineering applications such as back fill material in retaining structures, fill material in embankments, sub base material for construction of pavements, foundation base material and as fill material in land reclamation. This problem is to be addressed in such a manner that, the entire ash produced could be converted as a resource material by utilizing it completely. Soil stabilization is the process of treatment of soils to improve or modify their engineering behavior. The objectives of stabilization using admixtures are to control volume stability; improve strength, stress-strain characteristics, permeability, and durability; and to decrease erodibility and compressibility of soils. The mechanism of stabilization of the two commonly used inorganic stabilizers namely Portland cement and lime, are similar with formation of end products calcium silicate hydrates (C-S-H). The reaction mechanism of pond ash and cement resembles with that of the reaction mechanism soil and cement. Pond ash is a lightweight,

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cohesionless material and composed of silt-sized particles. It is a pozzolanic material and can be stabilized with the addition of various stabilizers like cement and lime. A pozzolan is defined as a siliceous or siliceous and aluminous material which itself possesses little or no cementitious property but which, in finely divided form and in the presence of moisture, will react with calcium hydroxide at ordinary temperature to form compounds possessing cementitious properties. The aim of present study is to carry out different laboratory test on cement stabilized pond ash, so as to see the effect of cement content on the strength properties of the mix. Various %age of cement was added to pond ash based on the result reported by Gyatri and Kaniraj (2012). Effect of curing period on strength was also studied. Flexural tests were also conducted for pond ash-cement-fiber reinforced mix for few specimens to see the effect of fiber.

EXPERIMENTAL PROGRAM

• Material

Pond ash used in the study was collected from Guru Gobind Singh Super Thermal Power Project (GGSSTP), Ropar, Punjab. OPC 53 grade cement (ACC brand) was procured from local market. Synthetic fiber (Recron-3s, a product of Reliance Industries), was used as reinforcement in this study. Different physical properties of pond ash were determined using standard method and have been given in Table 1 whereas the properties of fiber were obtained from the supplier and have been reported in Table 2.

Table 1: Physical Properties of Pond ash

S No. Parameter Value 1. Specific Gravity(G) 2.10 2. Plasticity NON PLASTIC 3. Maximum Dry Density (kN/m3) 11.01 kN/m3 4. Optimum Moisture Content (%) 27.4% 5. Angle of Internal Friction(φ) 33o

6. Cohesion (kN/m2) 1 kN/m2

7. Permeability (cm/sec) 1.24 x 10-4 cm/sec 8. Coefficient of Uniformity(Cu) 8.56 9. Coefficient of Curvature (Cc) 1.41

Table 2 Properties of Recron–3s

Sr. No Contents Values 1 Diameter of fiber 0.035 mm 2 Length of fiber 12.0 mm 3 Density of material 9.7 kN/m3 4 Aspect ratio of fiber (l/d) 343 5 Tensile strength 600 N/mm2 6 Melting point Over 2500C 7 Resistance to acid/alkali Good

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8 Dosage rate for concrete Use CT 2024 (12mm) at 909 g/m3

9 Dosage rate for plaster Use CT 2012 (6 mm) at 125 g/cement bag 1:4 cement/sand ratio

• Mix Proportions

Following mix proportion of pond ash and cement as shown in Table 3 were used.

Table 3 Mix proportions

Sr. No. Name of proportion PA : CEMENT 1 PA : CEMENT 97 : 03 2 PA : CEMENT 94 : 06 3 PA : CEMENT 91 : 09 4 PA : CEMENT 88 : 12 5 PA : CEMENT 85 : 15 6 PA : CEMENT 82 : 18

The Polypropylene percentages of 0.25, 0.50, 0.75, 1.0, 1.25 and 1.50 by weight were added

for the mix of sr. no. 2 and 3 only and after that flexural test were conducted. These mixes were selected based on the optimum relative increase in strength and considering the economy aspect.

• Tests

Laboratory tests (Standard proctor test, unconfined compression strength test, Tensile strength test, Flexural test) based on relevant Indian Standard were conducted on pond ash cement mix.

RESULTS AND DISCUSSION The result of compaction test has been shown in Figure 1 and 2. It can be seen from the figure that as the cement content in the mix increases from 3 % to 18 %, the maximum dry density increases and optimum moisture content decreases.

Fig 1: MDD v/s Cement content

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Fig 2: OMC vs Cement content

Results of unconfined compression test for different pond ash cement mixes are shown in

Figure 3. It can be observed from the figure that as the cement content increases unconfined compression strength (UCS) increases for a given curing period. Again for a given cement content, UCS increases with increase in curing period.

Fig 3: UCS vs Cement content

Tensile strength (TS) of different Pond ash cement mix was calculated using the formula

given below. A typical variation of Tensile strength with cement content after 28 days of curing is shown in Figure 4. Similar results were calculated for 7 and 14 days curing sample also, and has been reported elsewhere.

Tensile strength (T) = 2P/ π*D*L

Where P = Load in Newton and D = Diameter of specimen in mm

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Fig 4: Tensile strength v/s Cement content

Flexural strength (FS) of Pond ash Cement mix after 28 days of curing period was calculated after conducting two point flexural tests shown in Photograph 1. Figure 5 shows typical variation of Flexural strength with cement content after 28 days of curing.

Fig 5: Flexural strength v/s Cement content

Relative increase in Flexural strength (FS) was also determined and has been shown in Figure 6 for 28 days of curing period. Maximum relative increase in flexural strength occurs for 6 % and 9 % cement content.

Fig 6: Relative % increases in Flexural strength vs. Cement content

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Photograph 1 Typical failure pattern under 2 pt. loading

Synthetic fiber reinforcement was added in PA: CEMENT mixtures of 94:06 and 91:09 in

different percentage (0.25 %, 0.50 %, 0.75 %, 1.0 %, 1.25 %, and 1.50 %) by weight. Flexural test was conducted for this mix with 28 days curing period. Figure 8 show the variation of flexural strength with different %age of polypropylene fiber.

Fig 8: Flexural strength v/s Polypropylene (%)

CONCLUSIONS

Based on the study, following conclusions were drawn: 1. Increase in cement content increases the maximum dry density and decreases the

optimum moisture content. 2. Unconfined compressive strength increases with increasing cement content and curing

period. At a given cement content, unconfined compressive strength increases with increase in curing period.

3. Tensile and Flexural strength also increases with increase in cement content and curing period.

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4. Maximum relative improvement in Flexural Strength (FS) was obtained for the specimen, when cement content was 6 % and 9 % after 28 days curing.

5. Flexural strength increases with increase in fiber content up to 0.75% and after that any increase in fiber content does not improve the flexural strength any further.

References

Choudhary, A.K., Jha, J.N. & Gill, K.S. (2010). Laboratory investigation of bearing capacity behavior of strip footing on reinforced fly ash slope. Geotextiles and Geomembranes, 28(4): 393-402

Das, S. K., & Yudbhir (2005). Geotechnical characterization of some Indian fly ashes. International Journal of Materials in Civil Engineering, ASCE , 17,No.5, 544–552. Gill, K. S., Choudhary, A. K., Jha, J. N. and Shukla, S. K. (2013b). Large model footing load test on

reinforced coal ash slope. International Journal of Geotechnical Engineering, USA, 7(4) (in press).

Gayathri, V. and Kaniraj, S.R. (2012). “Geotechnical reuse of waste material-special focus to stabilized fly ash as pavement base course material.” Proceeding, Staff Development Programme (SDP) on Ground improvement and ground control including waste containment with geosynthetics, Ludhiana, India, 192-212. Kaniraj, S.R. and Havanagi, V.G; (1999); Geotechnical Characteristics of Fly Ash-Soil Mixtures);

Geotechnical Engineering Journal, 30(2):129–146. Kaniraj, S. R., & Gayathri, V. (2003). Geotechnical behavior of fly ash mixed with randomly oriented fiber inclusions. Geotextiles and Geomembranes, 21, No.3, 123–149. Kumar, V., Mathur, M. & Sinha, S. S. (2005). A case study: Manifold increase in fly ash utilization in India. Fly ash India 2005, Fly ash utilization programme (FAUP), TIFAC, DST, New Delhi, I, 1.1-1.8. McLaren, R. J., & Digioia, A. M. (1987).The typical engineering properties of fly ash. Proc.. Conf. on Geotechnical Practice for Waste Disposal, ASCE, New York, pp. 683–697. Senapati, M.R.(2011). Fly ash from thermal power plants – waste management and overview, Current Science, 100, No.12, 1791-1794. Sridharan A., Pandian N. S. & Srinivas, S. (2001). Compaction behaviour of indian coal ashes. Ground Improvement Journal, 5, No.1, 13-22.

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CBR IMPROVEMENT OF CLAYEY SOIL USING GEOGRID REINFORCEMENT

Pardeep Singh, Inderpreet Kaur and K. S. Gill Department of Civil Engineering, Guru Nanak Dev Engineering College, Ludhiana

Abstract: The quality and life of pavement is greatly affected by the type of sub-grade, sub base and base course materials. Being the lower most layer the type and quality of sub-grade soil influences the performance of flexible pavements in a big way. Highway development is one of the major components of infrastructure development in developing nations like India. Due to the heterogeneous nature of subsoil deposits, weak sub-grade soils are often encountered in most of the areas. The California bearing ratio (CBR) which is a governing criterion in the design of flexible pavements is very low in case of problematic soils and needs to be improved to confirm to the minimum standards of design guidelines. In the present investigation an attempt has been made to improve the weak sub-grade soils by using geo-grids as reinforcement. In this study commercially available geogrid was used as a reinforcement.. From the results it is clear that there is a considerable improvement in California Bearing Ratio (CBR) of sub-grade soils due to geo-grid reinforcement. In case of without reinforcement (Geo-grid) the soaked CBR value was 2.9% and maximum improvement was observed when geo-grid was placed at 0.2H from the top of the specimen and the CBR value increases to 9.4%. Keywords: CBR, Geogrids and flexible pavements

INTRODUCTION

The concept of reinforcement is not new; early civilizations commonly used sun-dried soil bricks as a building material. Somewhere in their experience it became an accepted practice to mix the soil with straw or other fiber available to improve the properties of virgin soil. Various materials were commonly used as reinforcement of both pavement materials and sub-grade soils. They can vary greatly, either in form (strips, sheets, grids, bars, or fibers), texture (rough or smooth), and relative stiffness (high such as steel or relatively low such as polymeric fabrics).

The prime factor influencing the structural design of a pavement is the load-carrying capacity of the sub-grade soil. IRC-37 guidelines are used for the design of flexible pavements in India. According to these guidelines subgade soil strength is measured in terms of CBR value, therefore CBR value is one of the important parameter which controls the thickness of a flexible pavement. This procedure requires that each layer should be thick enough to distribute the stresses induced by traffic so that when they reach the underlying layer they will not overstress and produce excessive shear deformation in the sub-grade soil. Each layer must also be compacted adequately so that traffic does not produce an intolerable amount of added compaction. In many countries throughout the world, the availability of good sub-grade soil, sub-base and base material which meets design specification is becoming increasingly difficult and to transport good quality materials from distant places is not economically feasible. Keeping in view the above stated problems lot of research work has been carried out by various research workers to improve the locally available weak materials by using some admixtures or reinforcing material (Haas, 1985,

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Nejad and Small,1996, Ling and Liu ,2001, Srinivas et al., 2008, Asha et al., 2010, Stalin et. al., 2010,). In most of the cases the effect of fiber reinforcement on CBR value of subgrade soils has been investigated in detail and very limited information is available pertaining to the effect of geogrids on CBR value. Though geo-grid reinforcement has already been used in RE walls with great confidence as the validated design methodology is available and geo-grids as a reinforcing material are proving to be cost effective alternative to the traditional methods. However to make use of the application of geo-grids for construction of roads over soft subsoil with more confidence, comprehensive research efforts are required. In this study an effort has been made in this regard.

The combined use of soil and a geo-grid may prove to be a better road design technique and the approach may be helpful in constructing the roads in areas where soil is highly compressible having very low load carrying capacity. Now a day’s various types of geo-grids are available commercially which are shown in Table-1 and can be used with more reliability.

Table-1: Various types of geo-synthetic reinforcement

Geo-synthetics Polymeric Materials Structures Application Areas Major Functions Geo-textiles Polypropylene(PP),

polyester ( PET), polyethylene (PE), polyamide (PA)

Flexible, permeable fabrics

Retaining walls, slopes, embankments, pavements, landfills, dams

Separation, reinforcement, filtration, drainage, containment

Geo-grids PP, PET, high-density polyethylene (HDPE)

Mesh-like planar product formed by intersecting elements

Pavements, railway ballasts, retaining walls, slopes, embankments, bridge abutments

Reinforcement separation

Geo-nets Medium-density polyethylene (MDPE), HDPE

Net-like planar product with small apertures

Dams, pipeline and drainage facilities

drainage

Geo-membranes PE, polyvinyl chloride (PVC), chlorinated polyethylene (CPE)

Impervious thin sheets

Containment ponds, reservoirs and canals

Fluid barrier/liner

Geo-composites Depending on geo-synthetics included

Combination of geo-textiles and geo-grids /geo-nets, geo-membranes and geo-grids

Embankments, pavements, slopes, landfills, dams

Separation, reinforcement, filtration, drainage

EXPERIMENTAL PROGRAMME

• Materials

Clayey soil used in this study was procured from near Sahnewal village. The various index and physical properties of this soil has been determined and given in Table-2.

• Geogrid

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Commercially available geogrid (SGi-040) was used as reinforcing elements. Fig. 3 shows the photograph of geogrid- SGi-040 whose properties are listed in Table 3.

Table 2: Physical properties and classifications of soil

Sr.No. Properties of soil Laboratory value

1. Specific Gravity(G) 2.70 2. Atterberg Limits (%)

Liquid Limit Plastic Limit

Plasticity Index

28.0 15.0 13.0

3. Indian Standard Classification CL(Clay of Low Compressibility) 4. Standard Proctor Test Results

Maximum Dry Density(kN/m3) Optimum Moisture Content(OMC) in %

17.0 16.0

Table 3: Properties of Geogrid (Strata India Ltd.)

Property Grid Mesh aperture size(nominal) mm 22 x 22

Tensile strength in longitudinal direction at 2% strain (kN/m) 5.8 Stiffness in longitudinal direction (kN/m) 290

Elongation in machine direction 16.5% Tensile strength in transverse direction at 2% strain (kN/m) 5.2

Stiffness in transverse direction (kN/m) 260

Elongation in transverse direction 10%

Fig 1: Geogrid (SGi-040)

• Preparation of Samples

CBR test samples were prepared in the conventional CBR mould at maximum dry density and optimum moisture content. As per the planning of this investigation geo-grids were placed in a

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single layer at different positions: 0.2H, 0.4H, 0.6H and 0.8H of the specimen height from the top surface. In order to eliminate the frictional resistance between the geo-grid and the wall of the CBR mould, the size of the geo-grid disc was kept 148mm i.e. 2mm less than the diameter of the CBR mould diameter. While placing the geogrid layer at its proper position a special care has been exercised to compact the soil layer to its maximum density by using predetermined number of blows of the hammer. A total number of thirty samples for unsoaked and soaked conditions at different positions of geo-grid were prepared and for each case average value of three samples is taken as the final result. In this way total 15 samples were tested for unsoaked condition and another 15 for soaked condition after keeping the sample in water for 96 hours. The load v/s penetration curves were drawn for each sample with geo-grid at different positions and the CBR values were calculated from these curves. It is clear that considerable amount of increase in CBR value of soil with geo-grid reinforcement and in case of unreinforced soil the CBR value is 2.9% and with geo-grid reinforcement the CBR value (soaked CBR) increases to 9.4%. The highest increase in the CBR value was achieved, when geo-grid was placed at 0.2H from the top of the specimen.

RESULTS AND DISCUSSION

Table-3 and Fig.2 showed that there is a substantial increase in CBR value both for unsoaked and soaked case when geo-grid layer is placed at the shallow depth from the top of the specimen. The CBR value is maximum for both unsoaked and soaked case when geo-grid layer is placed at 0.2H from the top of the specimen where H is the height of the specimen. Fig.2 shows that optimum value of H lies between 0.2H and 0.3H and similar trend is evident from Fig.3 for soaked case. The maximum increase of 147% and 224% was observed for both unsoaked and soaked case respectively when reinforcement layer is placed at 0.2H from the top of the specimen.

As the depth of reinforcement layer increases, the CBR value starts reducing for both the cases i.e. unsoaked and soaked. This type of behavior shown by the composite sample can be explained on the basis of stress distribution criterion. The stresses are maximum immediately below the plunger of the CBR apparatus; this may be the reason for maximum improvement in the CBR value when geo-grid layer is placed at shallow depth i.e. at 0.2H.

Table 3: Results of CBR Tests for Different Positions of Geo-grids

Sr. No. Position of geo-grid from top of specimen

Unsoaked CBR Soaked CBR

1. No geo-grid 6.5 2.9

2. 0.2H 16.05 9.4

3. 0.4H 13.86 7.2

4. 0.6H 10.9 5.8

5. 0.8H 7.2 3.16

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Fig 2:Effect of position of geogrid on the unsoaked CBR value

Fig 3: Effect of position of geogrid on the soaked CBR value

CONCLUSIONS

In the present study, reinforced benefits geo-grid layer at different depth from the top of specimen were evaluated in terms of their strength parameter i.e. CBR value (soaked CBR and unsoaked CBR) and the important findings of this research are summarized below:

(1) The CBR of a soil increases by when it is reinforced with a single layer of geo-grid. The amount of improvement depends upon the type of soil and position of geo-grid.

(2) The unsoaked CBR value increases from 6.5% for virgin soil to 16.05%, when geo-grid was placed at 0.2H and for greater depths of geo-grid layer, CBR value starts decreasing. This increase is 147%.

(3) In case of soaked CBR test, the CBR value increases from 2.9% to 9.4% for geo-grid position at 0.2H and for greater depth of layers the trend is similar to unsoaked case. This increase is 224%.

(4) As the CBR value is one of the important parameter controlling the thickness of a flexible pavement, huge saving in the cost can be achieved by reinforcing the subgrade soil with geo-grids.

References Asha et al., (2010), “CBR Tests on Geosynthetic Reinforced Soil-aggregate Systems” , Indian

Geotechnical Conference. Dean R Freitag (1986), soil randomly reinforced with fibers. Journal of Geotechnical Engineering,

ASCE, Volume 112, No.8, pp 823-826.

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Gosavi, M. Patil, K.A Mittal, S. Saran, S. (2004), Improvement of properties of black cotton soil sub-grade through synthetic reinforcement. Journal, Institution of Engineers (India), Volume 84, pp.257-262.

Haas, R., (1985), “ Structural Behavior Of Tensar Reinforced Pavement And Some Field Applications”,

Polymer Grid reinforcement, Thomas Telford Limited, London, UK, pp. 166-170 Indian Standard: 2720 (Part 16): 1987, Methods of tests for soil- part (16): Laboratory determination

of California bearing ratio. IRC: SP 72 (2007). Guidelines for the design of flexible pavement for low volume roads. Krishnaswamy, N.R. and Sudhakar, S. (2005). Analytical and experimental Studies on geo-synthetic

reinforced road sub-grade. Journal of Indian Road Congress, 66 (1), 151-200. Ling et al., (2001), “Performance Of Geosynthetic Reinforced Asphalt Pavements”, Journal of

Geotechnical Engineering, ASCE, Vol. 127, pp. 177-187 Nejad et al., (1996), “ Effect of Geo-Grid Reinforcement In Model Track Tests On Pavements ”,

Journal of Transportation Engineering, ASCE, Vol. 122(6), pp. 468-474. Subba Rao K.S (2000), Swell-shrink behavior of expensive soils, Geo-technical challenges. Indian

Geotechnical Journal, 30, 1-69. .

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UTILIZATION OF WASTE POLYMER IN CONSTRUCTION OF FLEXIBLE PAVEMENT

M. Mohanty, M. Panda and U. Chattaraj Department of Civil Engineering, National Institute of Technology, Rourkela, India

Abstract: Any material or object is said to be waste if it constitutes a scrap material or an effluent or other unwanted surplus substance arising from the application of any process; and requires to be disposed of as being broken, worn out, contaminated or otherwise spoiled. Broadly the waste is up to two types i.e. bio degradable and non bio degradable. Among these non-biodegradable waste plastic is the one of the most contributor which has a life span not less than 4500 yrs. The availability of the waste plastic is enormous, as the plastic materials have become the part and parcel of our daily life. They either mixed with municipal solid waste and/or thrown out over land area. If not recycled their present disposal is either by land filling or by incineration. For both the developing and developed country disposing plastic is a headache as improper disposal can cause breast cancer, reproductive problems in humans and animals, genital abnormalities and much more. Among various alternatives of re-use of plastic waste, the use of plastic in the construction of bituminous pavement is a challenge for the engineer as well as scientist to save the natural resources.This paper presents a brief study on use of waste polyethylene in modification of bituminous mixes used in flexible pavements.

INTRODUCTION

Any material which is not needed by the owner, producer or processor is called waste.Waste management is an important part of the urban infrastructure as it ensures the protection of the environment and of human health.Waste management is the collection, transport, processing (waste treatment), recycling or disposal of waste materials, usually ones produced by human activity, in an effort to reduce their effect on human health. It is not only a technical environmental issue but also a highly political one.

Today availability of plastic waste is enormous. Once used, plastic materials are thrown outside and they remain as waste. Plastic wastes are durable and non-biodegradable. These plastic wastes get mixed with water, disintegrate, and take the forms of small pallets which cause the death of fishes and other aquatic life who mistake them as food material. Sometimes they are either land filled or incinerated or plastic wastes get mixed with the municipal solid waste or thrown over a land area. Under these circumstances, an alternative use of these plastic wastes is required. So any method that can use this plastic waste for purpose of construction is always welcomed.

Now a day due to steady increase of wheel loads, tyre pressure, change in climatic conditions & daily wear and tear severely affect the performance of bituminous mix pavements. Hence any improvement in the property of the pavement is highly essential considering the present scenario. On the other hand these polyethylene / polypropylene bags are easily compatible with bitumen at specific condition.This paper presents a brief study on use of waste polyethylene in modification of bituminous mixes used in flexible pavements.

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DESIGN OF WASTE POLYTHENE MODIFIED BITUMINOUS MIX

There are two methods of preparing polythene modified bituminous mix. One is dry process and another is wet process. Aslam and Rahman (2009) observed that in case of wet process, plastic waste can be used as blending material. They cut polyethylene carry bags into small pieces using a shredding machine and sieved. Then the plastics pieces passing through 4.75mm sieve and retaining at 2.36mm sieve were collected and added slowly to the hot bitumen of temperature around 170-1800C. The mixture was stirred well using mechanical stirrer for about 20-30 minutes. Polymer-bitumen mixtures of different compositions were prepared and used for carrying out various tests. They had also tried for Dry process in which the aggregates were heated to around 1700C. Then shredded plastic-waste was added over hot aggregates with constant mixing to give a uniform distribution which got softened and coated over the aggregates. The hot plastic waste coated aggregates were then mixed with the hot bitumen 60/70 or 80/100 grade (1600C).

MATERIALS

• Aggregates Selection

In India aggregate should confirm the physical requirement laid by MORTH specification. Testing of aggregates such as sieve analysis, specific gravity, aggregate impact value and soundness are necessary.

• Bitumen Selection

In this country the bitumen used for road construction ranges in penetration grade from 20-225. Use of different grade of bitumen depends upon construction type and climatic condition. In hot climates lower penetration grade bitumen like 30/40 bitumen is preferred. Testing of bitumen such as penetration test, ductility test, viscosity test, softening point and specific gravity test are necessary.

• Selection of Waste Polymer

In general testing of polyethylene coated aggregates such as thermal study and coating tests are necessary. In this study, works are related to uses of waste LLDPE, LDPE, HDPE.

• Thermal Study

A study of the thermal behaviour of the polymers as carried out by Aslam and Rahman (2009) shows that the polymers as mentioned above softens easily without any evolution of gas around 130-1400C, which has been scientifically verified. At around 3500C, they get decomposed releasing gases like methane, ethane etc. and above 7000C, they undergo combustion producing gases like CO and CO2.

• Binding Property

Aslam and Rahman (2009) also carried out binding property test in which the aggregate was heated to around 1700C and the shredded plastic waste (size between 2.36mm and 4.75 mm) was added and compacted. According to them block was very hard with compressive strength not less than 130 MPa and binding strength of 500 kg/cm2. Soaking of polymer coated aggregate in water

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for 72 hours has also done by them. There was no stripping at all which shows that the coated plastic material sticks well with the surface of the aggregate.

WET PROCESS In the wet process the additives are blended with asphalt at specific temperature before mixing with aggregates. Xu et al. (2010) and Jahromi and Khodaii (2008) reported that polymers and fibers can make three-dimensional networking effect in Asphalt Concrete mixture and provide better adhesion between aggregate particles and asphalt binder. According to Yousefi (2009) the polyethylene particles do not tend to rip in bitumen medium and it was also shown that these particles prefer to join together and form larger particlesdue to interfacial and inter-particle attractive forces.

• Penetration Test of Modified Blend

Karim et al. showed that the penetration values of blends decrease depending upon the percentage of polymers added to them. So bitumen with higher content of polyethylene is suitable for warmer regions.

• Softening Point of Modified Blend

It was observed that the softening point increases by the addition of plastic waste to the bitumen. According to Aslam and Rahman (2009) higher the percentage of plastic waste added, higher is the softening point. The influence over the softening point may be due to the chemical nature of polymers added.

• Ductility

The ductility decreases by the addition of plastic waste to Bitumen. The decrease in the ductility value may be due to interlocking of polymer molecules with bitumen.

• Flash and Fire Point

Flash & fire point of plain Bitumen is 175-2100C. As per the study of Aslam and Rahman (2009) the inflammability of the blend decreases as the percentage of polymer increases. The blend has developed better resistance to burning. The polymer bitumen blend road surfaces will be less affected by fire hazards.

• Melting Point and Life Period

Verma (2008) studied that plastic increases the melting point of the bitumen and makes the road flexible during winters resulting in its long life. While a normal “highway quality” road lasts four to five years it is claimed that plastic-bitumen roads can last up to 10 years.

CHARACTERIZATION OF PLASTIC WASTE-BITUMEN BLEND FOR FLEXIBLE PAVEMENT

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• Stripping Test

Aslam and Rahman (2009) and Verma (2008) reported that even after immersion of aggregates coated with modified bituminous mix in water, there was no stripping. This shows that the blend has better resistance towards water.

• Marshall Test

Marshall Stability measures the maximum load sustained by the bituminous material at a loading rate of 50.8 mm/min. Karim and Gawandeaet al. (2012) concluded that the bitumen mixes result higher Marshall Stability value with higher percentages of polyethylene. Verma (2008) observed that a substantial increase in Marshall Stability value of the BC mix by using modified bitumen, in the order of two to three times higher value incomparison with the untreated or ordinary bitumen.

• Creep Test

Reinke and Glidden (2002) found that the resistance of HMA mixtures to failure using the DSR (dynamic shear rheometer) creep and recovery tests are improved by using polymer modified binders.

DRY PROCESS An alternate method was innovated to find an effective way of using higher percentage of plastic waste in the flexible pavement. The aggregate coated with plastic was used as the raw material. According to Gawandea et al. (2012) when aggregate get coated with plastics it improves its quality with respect to voids, moisture absorption and soundness. The coating of plastic decreases the porosity and helps to improve the quality of the aggregate and its performance in the flexible pavement.

• Stripping Test

Aslam and Rahman (2009) reported that the plastic waste coated aggregate bitumen mix prepared by the above process when immersed in water, even after 96 hours there was no stripping. This shows that the plastic waste coated aggregate-bitumen mix has good resistance towards water. When polymer is coated over aggregate, the coating reduces its affinity for water due to non-wetting nature of the polymer and this resists stripping. According to Vasudevan (2004) it can resist stripping and hence pot-hole formation is very much reduced. Marshall Characteristics Table 1.Properties of conventional and modified bituminous concrete mix at optimum binder content given

by Sabina et al. (2009)

Properties Conventional mix Modified mix, 8% polythene Marshall stability, kg 1300 1567

Flow, mm 3.8 6.5 Air void 4.5 3.5

Bulk density, g/cc 2.391 2.351 ITC, kg/cm2 6.4 10.7

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Fig 1: Results of Marshall Stability (Source Bindu et al. 2010)

Fig 2: Flow Results (Source Bindu et al. 2010)

Fig 3: Results of Bulk Density (Source Bindu et al. 2010)

Fig 4: Void in Mineral Aggregate Result (Source Bindu et al. 2010)

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Fig 5: Void Filled By Bitumen Results (Source Bindu et al. 2010)

• Indirect Tensile Strength and Rutting Test

According to Sabina et al. (2009) ITS can be calculated as

𝐼𝐼𝐼𝐼𝐼𝐼 = 2𝑃𝑃𝐴𝐴𝐴𝐴𝐴𝐴

(1)

Where; P=load in kg t=thickness in cm d=diameter in cm

Rutting potential can be determined by using Hamberg’s wheel tracking device. Sabina et al. (2009) observed that the indirect tensile strength and rutting shows significant improvement in its value with addition of polyethylene.

• Dioxin Formation

The fear about the formation of Dioxin, the toxic compound, during the heating of polymers is always in the mind of people. In the process of the preparation of polymer-bitumen aggregate mix, the temperature used is only ≈170°C and no chlorine or copper is present in the system. Vasudevan (2004) reported that there is no formation of Dioxin during the use of waste polymer for road construction. So it is a safe disposal of waste polymers.

• Effect of Bleeding

The increase in the softening point shows that there will be less bleeding during summer. Bleeding accounts, on one side, increased friction for the moving vehicles and on the other side, if it rains the bleedings accounts for the slippery condition. According to Vasudevan (2004) both these adverse conditions are much reduced by polymer- bitumen blend. Air void proportion around 4% is enough to provide room for the expansion of asphalt binder to prevent bleeding or flushing that would reduce the skid resistance of the pavement and increase rutting susceptibility. According to Awwad and Shbeeb (2007) the air void contents of the modified mixture are not far from that of the non-modified mixture.

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COMPARISON

• Advantages of wet process This Process can be utilized for recycling of any type, size, shape of waste material (Plastics,

Rubber etc.)

• Disadvantages of wet process 1. Powerful mechanical is required. 2. Additional cooling is required as improper addition of bitumen may cause air pockets in

roads. 3. Maximum % of waste plastic cannot be added. 4. Sometimes some stabilizing agent may be required.

• Advantages of dry process 1. Plastic is coated over stones which improves surface property of aggregates. 2. Coating is easy & temperature required is same as road laying temp. 3. Use of waste plastic in dry process is more than wet process. 4. Doubles the binding property of aggregates. 5. No new equipment is required. 6. Bitumen bonding is strong than normal. 7. The coated aggregates show increased strength. 8. No degradation of roads even after 5 -6 yrs after construction. 9. No evolution of any toxic gases as maximum temperature is 180ºC.

• Disadvantages of dry process The process is applicable to plastic waste material only. Because, it is impossible to coat

aggregate by any type of polymers.

CONCLUSIONS Extensive literatures have been reviewed on use of polyethylene and waste polyethylene in preparation of more useful and beneficial paving mixes. This review intended to find the effective ways to reutilize the hard plastic waste particles as bitumen modifier for flexible pavements. The use of modified bitumen with the addition of processed waste plastic helps in substantially improving the Marshall stability, strength, fatigue life and other desirable properties of bituminous mix, resulting which improves the longevity and pavement performance with marginal saving in bitumen usage. The process is environment friendly. It is expected that these waste materials which would have caused havoc in the solid waste management in a locality may be used in a more beneficial and economical way in road construction. References Aslam; Rahman S. U.; (2009); Use of waste plastic in construction of flexible pavement. Awwad M. T.; Shbeeb L.; (2007); The use of polyethylene in hot asphalt mixtures, American journal of

applied sciences; 390-396. Bindu C. S.; Beena K. S.; (2010); Waste plastic as a stabilizing additive in SMA; IJET; 2; 379-387.

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Gawandea A.; Zamarea G.; Rengea V. C.; Taydea S.; Bharsakaleb G.; (2012); An overview on waste plastic utilization in asphalting of roads; JERS; III; 01-05.

Jahromi S.; Khodaii A.; (2008); Carbon fiber reinforced asphalt concrete; AJSE; 33; 355–364. Karim R.; Islam N.; Sajjad M.; Habib A.; Polyethyelene, A Potential Solution to Strength Loss of

Bituminous Pavement Under Water; 204-207. Reinke G.; Glidden S.; (2002); Impact of polymer modified binders on the DSR creep properties of

HMA mixtures. Sabina; Khan T. A.; Sangita; Sharma D.K.; Sharma B.M.; (2009); Performance Evaluation of Waste

Plastic/ Polymers Modified Bituminous Concrete Mixes; JSIR; 68, 975-979. Vasudevan R.; (2004); Use of Plastics Waste in Construction of Tar Road; ENVIS; 2; 1-8. Verma S. S.; (2008); Roads from plastic waste; Sciencetech entrepreneur; 1-4. Xu Q.; Chen H.; Prozzi J.A.; (2010); Performance of fiber reinforced asphalt concrete under

environmental temperature and water effects; J.Constr. Build. Mater; 24(10), 2003-2010. Yousefi A. A.; (2009); Phase-Destabilization Mechanism of Polymer-Modified Bitumens in Quiescent

Annealing; Prog. Color Colorants Coat; 53-59.

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UTILIZATION OF PLASTIC WASTES AND WASTE RECYCLED PRODUCT AS HIGHWAY

MATERIALS IN FLEXIBLE PAVEMENT SYSTEM

A.K.Choudhary1, Ranjit Prasad2, K.S.Gill3 1Deptt. of Civil Engineering, National Institute of Technology, Jamshedpur

1Deptt. of Metrology and Material Science, National Institute of Technology, Jamshedpur 2,3Deptt. of Civil Engineering, Guru Nanak Dev Engineering College, Ludhiana

Abstract: An experimental study was carried out to investigate the CBR behavior of Waste Recycled Product (WRP), an industrial waste generated in steel plants with and without reinforcement. Waste plastic cut in the form of strips of constant width and varying lengths were used as reinforcing elements. The effect of waste plastic strip content (0.25% to 2.0%) and strip length on the CBR and secant modulus of strip reinforced WRP was investigated. The study reveals that addition of waste plastic strips of appropriate size and in appropriate proportions results in an appreciable increase in both the CBR and secant modulus. The waste plastic strip reinforced WRP can be used in low cost embankment/road construction leading to significant cost advantage as well as safe disposal of these waste materials in an environment friendly manner.

Key words: HDPE, CBR, Pavement, Reinforcement, Subgrade

INTRODUCTION

The development of a nation is linked with its industrial growth. With rapid industrialization, the quantity of wastes generated by the industries has also been increasing immensely creating huge problems of their disposal and environmental degradation. In developing countries like India, the environmental protection measures are limited in comparison to the expected industrial growth and therefore it is necessary that the researchers should focus their research in utilization aspects of these wastes. Geotechnical characterization of these industrial wastes is likely to provide economically viable and environment friendly solutions for their gainful utilization and thereby solving the problem of their disposal to a great extent.

Huge quantities of blast furnace slag is generated in the steel plants during the extraction of iron from iron ore which are normally dumped in and around the plant occupying huge land area apart from causing huge environmental pollution. It has also been observed that the slag which is normally discarded as waste; still has significant iron content which can be gainfully recovered through recycling. Keeping this in view, one Waste Recycling Plant was commissioned by Tata Steel, Jamshedpur in the year 1986 in order to extract the left out iron content from the slag. WRP; is a waste product generated after recycling of blast furnace slag in the Waste Recycling Plant. The annual average production of WRP in the Tata Steel is at present of the order of one million ton which is usually dumped in and around the city. WRP resembles to a cohesionless granular material and is observed to contain mostly the particles in the size range of sand.

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Soil reinforcement is an effective and reliable technique to improve the strength of soil subgrade. An improved subgrade shall require relatively thinner section of a flexible pavement as compared to that required in case of an untreated and weaker subgrade resulting in significant cost advantage. Over the years the use of geotextiles and other polymeric reinforcements such as geogrids has increased drastically in geotechnical engineering practice. However; in certain cases; especially for low cost embankment/road construction, their cost becomes a prohibitive factor for their wide spread use. In comparison to the systematically reinforced soil, randomly distributed fiber reinforced soil has been found effective in improving the California bearing ratio (CBR) of soil as reported in the literature [Gosavi et al. 2004, Yetimoglu et al. 2005]. Nowadays plastic containers usually made of high density polyethylene (HDPE) are being discarded immediately after use. Though, at many places HDPE is being collected for recycling or reuse but unfortunately; the secondary markets for reclaimed HDPE have not developed as recycling programs. According to the data published in US, plastic waste is occupying 20% of available landfill spaces by volume. The estimated municipal solid waste production in India upto the year 2000 was of the order of 39 million tons per year and is expected to touch 56 million tons per year by the end of 2010 [Dutta 1997]. The typical percentage of plastics in the municipal solid waste produced in India is around 1% [Rao and Dutta 2004]. The best way to handle HDPE wastes is to utilize them for engineering applications and soil reinforcement can be a significant secondary market for waste HDPE. Soil reinforcement with reclaimed HDPE strips, if found effective can provide an easy and economical means to improve the engineering performance of the soil subgrades which otherwise considered are unsuitable. Again it can help in solving the problem of disposal of this non biodegradable waste causing environmental hazards. The feasibility of reinforcing soil with strips of reclaimed HDPE has been investigated only to a limited extent by few researchers [Benson and Khire 1994] and therefore the prediction of pavement performance will become difficult if unconventional materials are part of pavement structure [Lee and Fishman 1993]. Keeping this in view an attempt has been made in the present investigation to demonstrate the potential for using reclaimed HDPE strips as soil reinforcement along with WRP, another waste for improving the performance of the subgrades and thus possibility of finding its applications in many real life problems especially for design and construction of low cost roads. The paper describes the results of a series of laboratory CBR tests carried out with specimens of unreinforced WRP as well as WRP mixed randomly with varying percentage of HDPE strip content and lengths. The results obtained from the tests are presented and discussed in this paper.

EXPERIMENTAL WORK

A brief description of the material and method [as per IS-2720-Part-I(1987)] used in this investigation is given in the following paragraphs.

• WRP

The investigation was carried out with WRP collected from Waste Recycling Plant of Tata Steel at Jamshedpur, India, having specific gravity 2.87, effective size (D10) as 0.075 mm, coefficient of uniformity (Cu) 8.67 and coefficient of curvature (Cc) 1.04. The WRP was classified as ‘SW’ as per I.S 1498. Figure 1 shows the grain size distribution curve of WRP. The maximum and minimum dry densities of WRP as determined from the relative density test were 23.15 kN/m3 and 19.91kN/m3 respectively.

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Figure 1 Grain size distribution of WRP

• HDPE

The waste plastic strip used in the present study were purchased from a rag picker who collects recycling materials from the waste dump site in and around Jamshedpur, Jharkhand (India) at a price of INR 100 per kg (approximately $2per kg). They are made of HDPE having a width of 12mm and a thickness of 0.40mm. These were cut into lengths of 12mm (aspect ratio=1), 24mm (aspect ratio=2) and 36mm (aspect ratio=3) thus always ensuring that mould diameter remains at least four times the maximum strip length in order to ensure that there is sufficient room for the strips to deform freely and independent of mould confinement (Choudhary et al 2010b). The waste plastic strips to be added to the soil were considered a part of the solid fraction in the void solid matrix of the soil. The content of the strip is defined herein as the ratio of weight of strips to the weight of dry WRP. The tests were conducted at a strip content of 0.0%, 0.25%, 0.50%, 1.0%, and 2.0% respectively. In the absence of standards for testing strips, the standard used for wide width tensile strength test (ASTM D 4885) for geosynthetics were used. The tensile strength of 100mm long waste plastic strip was determined at a deformation rate of 10mm/min in a computer controlled Housefield machine. The average ultimate tensile strength of this strip was 0.36 kN and percent elongation at failure was 23%.

• Method

The experimental study involved performing a series of laboratory CBR tests on unreinforced and randomly oriented HDPE strip reinforced WRP specimen. Specimens were prepared by compacting WRP in dry state in three equal layers to a dry density of 17.54 kN/m3 (corresponding to a relative density of Dr= 85%) in a steel CBR mould of 150 mm diameter which is 175 mm high. HDPE strip reinforced WRP layers were prepared at the same dry density as that for unreinforced specimen. Required amount of strips as well as WRP for each layer were first weighed and then the strips were randomly mixed in dry state and due care was taken so as to have

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a homogeneous mix. The mix was then transferred to the mould. A surcharge base plate 148 mm in diameter weighing 25 N was then placed over it in order to avoid segregation of the strips during vibration. The mix was compacted in the mould by vibrating it on a vibration table for 2 minutes. Similar procedure was adopted for compacting other two layers in the mould. The tests were performed as per procedures described in IS-2720-Part 16(1987). A surcharge plate of 2.44 kPa was placed on the specimen prior to testing. The loads were carefully recorded as a function of penetration up to a total penetration of 12.5 mm. Finally; load-penetration curves were drawn for each case and corrections were applied wherever required using the standard procedure. From the load-penetration curves so obtained California bearing ratio (CBR) values as well as secant modulus (ratio of load in kPa at a penetration of 5.0 mm to the penetration of 0.005m) were determined. Since for all the cases considered in the present investigation, CBR value at 5.0 mm penetration was observed higher than that of 2.5 mm penetration even on repetition, therefore the CBR value reported in the present investigation are those of 5.0 mm penetration.

RESULTS AND DISCUSSION

The load-penetration curves obtained from the CBR tests for un-reinforced and randomly reinforced system with varying strip contents (0.25% to 2.0%) and aspect ratios (AR=1, 2 and 3) are shown through Figure 2 to Figure 4.

Fig 2: Load penetration curve for varying strip content (AR=1)

0

500

1000

1500

2000

2500

0 2 4 6 8 10 12 14

Penetration (mm)

Loa

d x

0.01

(kN

)

0%0.25%0.50%1.00%2.00%

AR=1 Strip Content(% )

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Figure 3 Load penetration curve for varying strip content (AR=2)

Figure 4 Load penetration curve for varying strip content (AR=3)

It is evident from these figures that in general, addition of randomly oriented HDPE strips inclusion in the WRP increased the CBR value significantly when compared to that obtained in case of unreinforced WRP. The detailed outline of the test results are presented in Table-1.

0

500

1000

1500

2000

2500

0 2 4 6 8 10 12 14

Penetration (mm)

Loa

d x

0.01

(kN

)

0%

0.25%

0.50%

1.00%

2.00%

AR=2 Strip Content(% )

0

500

1000

1500

2000

2500

3000

0 2 4 6 8 10 12 14

Penetration (mm)

Loa

d x

0.01

(kN

)

0%

0.25%

0.50%

1.00%

2.00%

AR=3 Strip Content(% )

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Table-1: Outline of Test Results

S. No.

Aspect Ratio

Strip Content (%)

California Bearing Ratio (%) CBRI Secant Modulus (MPa)

PLR 2.50 mm 5.0mm

1. U.R Nil 32.85 41.85 1.00 858.10 1.00 2.

1.0

0.25 38.32 49.88 1.19 1024.71 1.51 3. 0.50 47.81 66.23 1.58 1380.20 1.52 4. 1.0 52.63 70.17 1.68 1441.32 1.62 5. 2.0 58.16 74.16 1.77 1522.81 1.79 6.

2.0

0.25 39.49 59.85 1.43 1229.45 1.53 7. 0.50 51.46 71.00 1.70 1457.22 1.59 8. 1.0 52.63 74.99 1.79 1541.14 1.80 9. 2.0 71.75 88.08 2.10 1809.03 1.81 10.

3.0

0.25 47.88 60.24 1.44 1236.58 1.77 11. 0.50 65.84 82.58 1.97 1695.97 1.85 12. 1.0 67.00 88.56 2.12 1817.13 1.90 13. 2.0 76.57 96.35 2.30 1978.12 2.11

It can be seen from Table-1 that the CBR values of the unreinforced WRP corresponding to 2.5mm and 5.0mm penetration were found to be 32.85 % and 41.85 % respectively which increased to 38.32% and 49.88% respectively when the WRP was reinforced with 0.25% waste plastic strips having aspect ratio equal to 1.

In general , it is seen that for a given aspect ratio, the CBR values increases with increase in strip content (0.25% to 2%) whereas for a given strip content it increases with increase in strip length (AR= 1,2 and 3).

The extent of improvement in the CBR values due to the addition of HDPE strip inclusions has been expressed by a dimensionless term in literature(Choudhary et al. 2010a) by california bearing ratio index (CBRI) which is defined as the ratio of CBR value of reinforced soil (CBRr) to the CBR value of unreinforced soil (CBRu).

CBRI = CBRr/CBRu

The variation of CBRI with strip content at various strip lengths has been indicated in Table-1.

Increase in strength due to the inclusion of waste plastic strips can also be expressed in terms of piston load ratio. Increase in piston load due to the presence of waste plastic strips has been expressed by a dimensionless term known as piston load ratio (PLR) which has been defined as ratio of maximum piston load at 12 .5mm penetration for HDPE strip reinforced WRP (Lr) to the maximum piston load at the same penetration for unreinforced WRP (Lu).

PLR = Lr/Lu

Piston load ratio (PLR) for strip content at different aspect ratios has been calculated and tabulated in Table-1. It is seen that the piston load increases with increase in strip content and strip length. It can also be observed that the piston load for reinforced system having aspect ratio 3 is almost two times as high as that of an unreinforced system.

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The variation in secant modulus of strip reinforced sand with strip content and strip length is shown inTable-1. As expected the increase in secant modulus is again noticeably attributed to strip inclusions in the soil and strip length. For example the secant modulus of the unreinforced WRP is 858.10 MPa. Addition of 0.25% of waste plastic strips having strip length 12mm increased the secant modulus to 1024.71 MPa. When the strip content was increased to 2% without changing the strip length, the secant modulus further increased to 1522.81 MPa. Table-1 further reveals that secant modulus also increases with the increase in strip length even when there is no change in the strip content. For example the secant modulus at 2% strip content having strip length 24 mm is 1809.3 MPa. When the strip length changes from 24 mm to 36 mm without change in strip content, it can be observed from the figure 8 that secant modulus increases to 1978.12 MPa. A similar trend was observed for other strip contents also.

The maximum CBRI and secant modulus value of a reinforced system is approximately 2.3 times as high as that of an unreinforced system, which occurs for the case when 2% HDPE strip having aspect ratio equal to 3 is mixed with the WRP.

After the completion of each test; specimens were dissected and the strips were visually examined. Many of the strips showed elongation, thinning and clear impression of WRP particles. Apparently, as the WRP particles sheared during penetration, strips embedded in the WRP got elongated due to the interface friction. Generally the CBR value at 2.5mm penetration is higher; however in the present study, the CBR value of HDPE strip reinforced sand at 5.0mm penetration is found to be higher than those at 2.5mm penetration. This indicates that at higher deformations the HDPE strip reinforcement is more effective in improving the strength of WRP as the full interface frictional resistance gets mobilized and consequently increases the resistance to penetration.

CONCLUSIONS

Based on the results of the present investigation following conclusions can be drawn: • The addition of reclaimed HDPE strips; a waste material to WRP results in an

appreciable increase in the CBR and the secant modulus. • The reinforcement benefit increases with an increase in strip content and the aspect ratio

and maximum value of CBR and secant modulus of a reinforced system is around 2.3 times of that of an unreinforced system.

• Though the maximum improvement in CBR and secant modulus is obtained when the strip content is 2% and the aspect ratio 3.

However further study is needed to: (i) optimize the size and shape of strips (ii) assess the durability and aging aspects of the strip reinforcement. Large scale tests are also needed to determine the boundary effects influence on the performance of such soils.

ACKNOWLEDGEMENT

The facilities extended during the study by NIT, Jamshedpur is acknowledged.

References Benson, C.H. and Khire, M.V. (1994) “Reinforcing sand strips of Reclaimed High density

polyethylene” Journal of Geotechnical Engineering, 120 (5), 838-855.

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Choudhary, A.K, Jha,J.N & Gill,K.S. (2010a), ”Utilization of Plastic Wastes for Improving the Sub-grades in Flexible Pavements” Proc. ASCE Geotechnical Spl. Publication No.203, Int. Conf. GeoSanghai 2010,pp320-326.

Choudhary, A.K, Jha, J.N & Gill, K.S. (2010b) “A Study on CBR Behavior of Waste Plastic Strip Reinforced Soil” Emirates Journal of Engineering Research, UAE University. 15(1), pp.51-57.

Dutta , M. (ed.) (1997) “ Waste disposal in engineered landfills” NPH, N.Delhi, 3-4 Gosavi, M. Patil, K.A., Mittal, S. and Saran, S. (2004) “Improvement of Properties of black cotton soil

subgrade through synthetic reinforcement” Journal, Institution of Engineers (India), Vol. 84, 257-262.

Lee,S.W. and Fishman, K.L.(1993) “Waste products as Highway Materials in flexible pavement System” Journal of Transportation Engineering, 119 (3) 433-449

Rao, G. V. and Dutta, R.K. (2004) “Ground improvement with plastic waste “Proceeding, 5th International Conference on Ground Improvement Technique, Kaulalumpur, Malaysia, 321-328.

Yetimoglu, T., Inanir, M., Inanir, O. (2005) “A study on bearing capacity of randomly distributed fibre reinforced sand fill overlying soft clay” Geotextile and Geomembranes, 23(2), 174-183.

IS: 2720-Part XVI(1987). Laboratory determination of CBR. Bureau of Indian Standards, New Delhi India.

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TESTS ON UNCONTROLLED BURNT RICE HUSK ASH AND CEMENT MIX

H. K. Khullar, K. S. Gill, Harvinder Singh and Charnjeet Singh Department of Civil Engineering, Guru Nanak Dev Engineering College, Ludhiana

Abstract: Most of the time rice husk is being burnt under uncontrolled condition when used as a fuel in the boilers and is being disposed over the ground which creates a lot of environmental hazards. The focus of the paper is to evaluate the effectiveness of using rice husk ash (RHA) as a construction material particularly when it is being burnt under uncontrolled condition. The paper presents the influence of different mix proportions of cement and RHA on compaction, unconfined compression strength and flexural strength. The results show that addition of cement in uncontrolled burnt RHA enhances its the strength and can be considered as an alternative construction material.

INTRODUCTION

Rice husk is a major agriculture byproduct obtained from the food crop of paddy. For every 4 tons of rice 1 ton of rice husk is produced. The husk is disposed of either by dumping it in an open heap near the mill site or on the roadside to be burnt. Disposal of rice husk is an important issue in the countries, which cultivate large quantities of rice. Rice husks have very low nutritional value and it take long time to decompose for converting into manure. Burning rice husk (RH) generates about 15-20% of its weight as ash. The ash being very light is easily carried by wind and water in its dry state. It is difficult to coagulate and thus contributes to air and water pollution. Cumulative generation of ash requires a large space for disposal which is difficult for developing country like India where land population ratio is very small. Utilization of rice husk ash (RHA) by exploiting its inherent properties is the only way to solve the environmental and disposal problem of the ash. A number of researchers have studied the physical and chemical properties of rice husk ash. Rice husk ash alone cannot be used for stabilization because of the lack of cementitious properties. The high percentage of siliceous material in rice husk ash indicates that it has potential pozzolonic properties. The normal method of conversion of husk to ash is incineration. The properties of rice husk depend whether the husks have undergone complete destructive combustion or have been partially burnt. RHA which is not being produced under controlled conditions by dying units and power generating units are generally considered not possessing pozzolanic properties and are not being used in any engineering projects. Many researchers have reported the characteristics of rice husk ash produced under controlled burning conditions and recommended its use in cement concrete, cement mortars and soil stabilizations by using different mixes e.g. cement-rice husk ash –soil or lime-rice husk ash-soil mixes (Rahman 1987, Jha and Gill 2006). But best way of disposal of rice husk ash produced under uncontrolled condition is to use this as constructional material by stabilizing it with some cementations material so that it can be utilized in bulk quantity in embankments of roads, railways or canals. The aim of present study is to investigate the compaction and strength properties of rice husk ash produced under uncontrolled burning conditions after adding different cement percentages from 3%, 6%, 9%, 12%, 15% and 18%.

EXPERIMENTAL PROGRAMME

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• Materials

Rice husk ash (RHA) was procured from from M/s Vardhman spinning Mill sector 32 Ludhiana. Physical and chemical properties of RHA are given in Table 1. Cement OPC 53 grade (ACC Brand) purchased from local market was used throughout the study. Physical properties of cement are given in Table 2.

Table 1 Properties of Rice Husk Ash

Chemical Properties Physical Properties Component %age Property Values Silica (SiO2) Alumina (Al2O3 ) Iron Oxide (Fe2O3 ) Lime (CaO) Magnesia Oxide

(MgO) Potassium (K2O) Other oxides

91.58 1.95 0.48 0.78 0.58 2.92 1.71

Specific gravity Grain Size analysis: Gravel

(%) Sand

(%) Silt and Clay

(%) MDD (kN/m3) OMC (%) Un-soaked CBR (%)

1.987 0 53.4 46.6 9.15 53.4 6.1

Table 2 Physical Properties of Cement

Property Value Fineness 318 m2/Kg Soundness 0.5 mm. Setting time Initial Setting Time (Min.) Final Setting Time (Min.)

120 185

Compressive strength: 3 days 7 days 28 days

36.5 MPa 45 MPa 55 MPa

• Mix Proportions

RHA and cement were mixed thoroughly in proportions given below in the Table 3.

Table 3 Mix Proportions Sr. No.

Name of Proportion Proportion of RHA : Cement

1 RHA: Cement 100:00 2 RHA: Cement 97:03 3 RHA: Cement 94:06 4 RHA: Cement 91:09 5 RHA: Cement 88:12 6 RHA: Cement 85:15 7 RHA: Cement 82:18

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• Laboratory Tests

Compaction test, unconfined compression test, California bearing ratio test, flexural test and durability tests were conducted as per the Indian Standard methods. Flexural Strength test is conducted to evaluate different characteristics of embankment, sub grade and sub base material for proper design and better performance. Due to the effect of repetitions of wheel loads, component layers of pavement are stressed due to flexural bending, fatigue cracking is observed due to tension. Flexural strength is indirect way to measure the tensile strength of stabilized base or sub base materials. Flexural strength test of stabilized soil is evaluated by using simple beam with third point loading [IS: 4332 (Part 6) 1972]. Soil stabilization causes alternation of soil to improve its engineering performance. Schematic representation is shown in Figure 1.

Fig 1: Schematic Diagram of Flexural Test by third point loading method

RESULTS AND DISCUSSION

Heavy compaction tests were conducted as per standard method for all the mixes. It can be observed from the Figure 2 that when cement content increases from 0 % to 18 %, maximum dry density increases from 9.15 kN/m3 to 10.15kN/m3. Similarly Figure 3 indicates that increase in cement content (0 % to 18 %) actually decreases the optimum moisture content (OMC) from 53.4 % to 40 %.

Fig 2: Variation of MDD with Cement Content

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Fig 3: Variation of OMC with Cement Content

Again unconfined compression test was conducted for all the seven mixes by changing the curing time from 7 days to 28 days as per Indian standard. Results of unconfined compression tests are reported in Table 4 and figure 4. It can be observed from the Figure 4 that for a given curing period, unconfined compression strength (UCS) increases with increase in cement content. Again for a given cement content, UCS increases with increase in curing period. Photograph 1 shows the sample after 28 days curing.

Photograph 1 Sample for unconfined compressive strength after 28 days curing

Table 4: UCS of different proportions of RHA: Cement at 7, 14 & 28 days curing periods

S.No. By Weight of mix UCS (N/mm²)

RHA (%) Cement (%) 7 Days Curing 14 Days Curing 28 Days Curing 1 97 3 0.371 0.512 0.858 2 94 6 0.529 0.673 1.000 3 91 9 0.653 0.791 1.123 4 88 12 0.767 0.902 1.264 5 85 15 1.042 1.110 1.418 6 82 18 1.349 1.423 1.566

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Fig 4: Variation of UCS with Cement Content (7days, 14days and 28days curing)

Fig 5: variation of Flexural strength with Cement Content

The modulus of rupture (R) was calculated using the following formula

R= Pl/bd2 (weight of the beam neglected)

Where R = modular of rupture in N/mm2, P= maximum load ( Newton), l = span length( mm); b = average width of specimen ( mm) and d = average depth of specimen in mm.

Figure 5 shows the result of variation of flexural strength due to increase in cement content in the mix after 28 days curing, whereas photograph 2 shows the picture of flexural test. Figure 6 shows the relative increase in flexural strength as the cement content increases.

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Photograph 2: Flexural test being performed in the laboratory

Fig 6: Relative increase of Flexural strength with cement content

CONCLUSION

Following conclusions can be drawn from the present study and it is applicable for the condition reported in this study.

1. Maximum dry density of uncontrolled burnt RHA increases and OMC decreases with increase in cement content.

2. Unconfined compression strength increases of uncontrolled burnt RHA increases with increase in cement content and curing period.

3. Flexural strength of uncontrolled burnt RHA also increases with increase in cement content and curing period.

References

Rahman, M.A. “Effects of cement –rice husk ash mixtures on geotechnical properties of lateritic soil” Soil and Foundations, 27(2), 1987, pp. 61-65

Jha, J.N. and Gill, K.S. (2006) “Effect of rice husk on lime stabilization” Journal of Institution of Engineers (India), Vol. 87, pp 33-39

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CONSTRUCTION OVER CLOSED LANDFILL

P. Y. Sarang1, P. P. Savoikar2, and C. S. Gokhale3 1 Lecturer, Angel Polytechnic, Verna-Goa, India

2 Head of Civil Engineering Department, Government Polytechnic, Bicholim-Goa, India 3 Principal, Don Bosco Engineering College, Margao-Goa, India

Abstract: As developable space is becoming scarce and costly in urban areas, development on top of the landfill and adjacent to old landfills has become increasingly common. Construction on old landfills (closed) is a challenging task as the behavior of waste is complex and difficult to characterize. The engineering challenges associated with development of old landfills include structural challenges such as differential settlement of the structures, foundation design in the case of lined landfills, construction and utility alignment whereas the environmental challenges such as mitigation of explosion due to accumulation of methane gas and health risks. With increasing amount of solid waste produced every year and scarcity of landfill spaces, closed landfills are being used beneficially today as demand for usable land increases. There has been an expansion of the possibilities from wildlife habitats, parks and golf courses to retail buildings, family homes, offices and parks. The sites that are being built on are mainly municipal solid waste (MSW) landfills. Post-closure development of landfills includes both hard development and soft development. Hard uses such as commercial, industrial, and infrastructure facilities whereas soft uses such as golf courses, amphitheatres, vegetation, irrigation and athletic fields. Geosynthetic reinforcements are also used for foundation stabilization. The engineered system to control landfill gas migration includes a membrane barrier beneath the slab, a venting system beneath the barrier to minimize the build-up of gases beneath the barrier. Recent advancement in landfill technology such as bioreactor landfills, sustainable landfill and piggy back landfill are practiced nowadays as a solution for increasing amount of solid waste and scarcity of landfill spaces. A suitable approach in municipal solid waste (MSW) management will deliver both environmental and economic sustainability.

Keywords: Municipal waste,post closure development bioreactor, sustainable, piggyback, landfills.

INTRODUCTION

As developable space is becoming scarce and costly in urban areas, development on top of the landfill and adjacent to old landfills has become increasingly common. Construction on old landfills (closed) is a challenging task as the behavior of waste is complex and difficult to characterize. The engineering challenges associated with development of old landfills include structural challenges such as differential settlement of the structures, foundation design in the case of lined landfills, construction and utility alignment whereas the environmental challenges such as mitigation of explosion due to accumulation of methane gas and health risks.

Closed landfills are being used beneficially today as demand for usable land increases. Landfill sites have been increasingly developed for high-value, productive land uses. There has been an expansion of the possibilities from wildlife habitats, parks and golf courses to retail buildings, family homes, offices and parks. The sites that are being built on are mainly municipal

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solid waste (MSW) landfills. Landfills can be wonderful sites for real estate development. Many closed landfills in urban areas have been converted to reserves/parks (public open space or sports fields) and are managed for recreation whereas rural areas have either reverted to the surrounding agricultural use (grazing), been used for forestry, or remain unused. The above developments on landfills are termed as soft developments. Hard developments over landfills include construction of huge structures like multistoried residential and commercial buildings, hotels and other recreational facilities. Post-closure development of landfills includes both hard uses such as commercial, industrial, and infrastructure facilities and soft uses such as golf courses, amphitheatres, vegetation, irrigation and athletic fields. Post-closure total settlement can approach 20 percent of the waste thickness, with differential settlement up to half that value. Construction of taller structures using pile foundations is generally restricted to landfills without an engineered bottom liner system. Shallow foundation systems for construction on top of landfills are typically limited to relatively light structures one or two stories tall, due to settlement considerations. Deep foundations bearing on firm strata beneath the waste may be used to support heavier structures. Both deep and shallow foundation systems require engineered systems to control landfill gas migration. The building protection systems typically include a membrane barrier beneath the slab, a venting system beneath the barrier to minimize the build-up of gases beneath the barrier, and an alarm system within the structure.

Currently, such post closure developments are permitted after 15 years after closure of landfills so that almost 100% of settlement of landfills is over. Such developments are novel ways of saving/recovering the huge cost of urban land which is already covered by landfills and is considered to be the waste. Closed landfill sites have been used for a variety of post closure land uses. Projects have ranged from parks, recreational facilities (Cooper et al., 1997, Castelao et al., 1999, Kissida et al., 2001), commercial or industrial developments such as container storage facilities, office facilities, shopping centres (Hinkle et al., 1990, Gifford et al., 1990, Bote & Andersen, 1997, Rollin & Fournier, 2001), motorway embankments (Perelberg et al., 1987), elevated highways, piled roadways or expressways (Oteo & Sopena, 1993, Shimizu, 1997, Yang and Anandarajah, 1998), to high rise buildings (Hirata et al., 1995). Some of such developments are shown in Fig 1 and 2.

Fig 1: Retail Store on Top of the closed Landfill at San fransisco, California

(Bouazza and Kavazanjian, 2001)

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Fig 2: Golf Course on Top of the closed Landfill at Fullerton, California

(Bouazza and Kavazanjian, 2001)

GEOSYNTHETIC REINFORCEMENT IN LANDFILLS

Geosynthetic materials have become critical components in the design and performance of mining facilities. Geosynthetic materials are now commonly used for containment of process solutions in heap leach pads, process and overflow ponds, tailings impoundments, and waste rock facilities. Geosynthetic materials are also used in foundation stabilization, mine reclamation, surface water diversion structures, and in environmental projects (revegetation and erosion control).Due to the nature and location of mining projects, the performance envelope of geosynthetic materials is often pushed beyond the limits of typical design procedures and recommendations.

• Different Types of Geosynthetics Used in Landfills

Geogrids can be used to reinforce slopes beneath the waste as well as for veneer reinforcement of the cover soils above geomembranes (Zornberg et al. 2001

Geonets are unitized sets of parallel ribs positioned in layers such that liquid can be transmitted within their open spaces. Their primary function is in-plane drainage.

Geomembranes are relatively impermeable sheets of polymeric formulations used as a barrier to liquids and/or vapors. The most common types of geomembranes used in landfills are high density polyethylene (HDPE).

Geocomposites represent a subset of geosynthetics whereby two or more individual materials are utilized together.

Geosynthetic clay liners (GCLs) represent a composite material consisting of bentonite and geosynthetics. The geosynthetics are either geotextiles or a geomembrane.

Geopipes are commonly used in landfill applications. A geopipe system is used in the sand or aggregate leachate collection layer to facilitate collection and rapid drainage of the leachate to a sump and removal system.

Geotextiles are common components in landfills, they are used for filtration purpose or as cushion to protect the geomembrane from puncture. Geotextiles are also used occasionally to reinforce the waste mass in order to increase its global stability (Gisbert et al. 1996).

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Geocells are three-dimensional, expandable panels made from HDPE or polyester strips. Geocell applications include protection and stabilization of steep slope surfaces and reinforcement of sub base of bottom liners.

Moreover, the foundation soil below the bottom of the landfill may be stabilized as shown in the Fig.3 using randomly distributed fiber reinforcements, while the steep side soil slopes beneath the liner could also be reinforced using geogrids.

Fig 3: Potential Foundation Alternative (from Bouzza and Kavazanjian, 2001)

RECENT ADVANCEMENTS IN LANDFILL TECHNOLOGY

• Bioreactor Landfill

In the bioreactor landfills, biodegradation of municipal solid waste (MSW) is accelerated by leachate recirculation. Bioreactor landfills accelerate the process of decomposition. As decomposition progresses, the mass of the landfill declines, creating more space for dumping garbage. Bioreactor landfills are expected to increase this rate of decomposition and save up to 30% of space needed for landfills. With increasing amounts of solid waste produced every year and scarcity of landfill spaces, bioreactor landfill can thus provide a significant way of maximizing landfill space. This is not just cost effective, but since less land is needed for the landfills, this is also better for the environment. Most landfills are monitored for at least 3 to 4 decades to ensure that no leachate or landfill gases escape into the community surrounding the landfill site. In contrast, bioreactor landfill are expected to decompose to level that does not require monitoring in less than a decade.

A bioreactor landfill is a sanitary landfill site that uses enhanced microbiological processes to transform and stabilize the readily and moderately decomposable organic waste constituents within 5–8 years of bioreactor process implementation. The bioreactor landfill significantly increases the extent of organic waste decomposition, conversion rates of complex organic compounds and process effectiveness over those which would otherwise occur within the traditional landfill sites. Stabilization means that the environmental performance measurement parameters (LFG composition and generation rate, and leachate constituent concentrations) remain at steady levels, and should not increase in the event of any partial containment system failures beyond the life time of the bioreactor process.The bioreactor landfill is an extension of leachate recirculation in landfilling,,refer Fig.4.

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Fig 4: Bioreactor Landfill

• Working of a Bioreactor Landfill

There are three types of bioreactors: aerobic, anaerobic and a hybrid (using both aerobic and anaerobic method). All three mechanisms involve the re-introduction of collected leachate supplemented with water to maintain moisture levels in the landfill. The micro-organisms responsible for decomposition are thus stimulated to decompose at an increased rate with an attempt to minimise harmful emissions.

Aerobic - Leachate is removed from the bottom layer, piped to liquids storage tanks, and recirculated into the landfill in a controlled manner. Air is injected into the waste mass, using vertical or horizontal wells, to promote aerobic activity and accelerate waste stabilization.

Anaerobic - Moisture is added to the waste mass in the form of recirculated leachate and other sources to obtain optimal moisture levels. Biodegradation occurs in the absence of oxygen (anaerobically) and produces landfill gas. Landfill gas, primarily methane, can be captured to minimize greenhouse gas emissions and for energy projects.

Hybrid (Aerobic-Anaerobic) - The hybrid bioreactor landfill accelerates waste degradation by employing a sequential aerobic-anaerobic treatment to rapidly degrade organics in the upper sections of the landfill and collect gas from lower sections. Operation as a hybrid results in an earlier onset of methanogenesis compared to aerobic landfills.

• Advantages of bioreactor landfills

Engineered bioreactor landfills have the following advantages, if properly implemented and managed:

1. Enhance the LFG generation rates 2. Reduce environmental impacts 3. Production of end product that does not need landfilling 4. Overall reduction of landfilling 5. Reduction of leachate treatment capital and operating cost 6. Reduction in post-closure care, maintenance and risk 7. Overall reduction of contaminating life span of the landfill

• Sustainable Landfill

Sustainable landfill is defined as a landfill that has the ability to provide the needs of waste disposal for future generation without exhausting its capacity. This can be accomplished through

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the use of modified bioreactor landfill and subsequent mining. It is a further advancement of bioreactor technology (Hettiarachi 2006). It involves three stage landfill operations. Landfill liner and leachate collection systems are used to minimize ground water contamination and maximize recovery of leachate. Daily, intermediate and final covers are provided to manage gas emissions and liquid entry. A gas collection system is installed for landfill gas collection and emission control. In addition to these typical sanitary landfill installations, pipe systems are added to re-circulate the collected leachate, as well pump air into the waste matrix during the second stage aerobic operation to accelerate biological degradation. The three stages of sustainable landfill are described in detail below:

• Anaerobic decomposition with gas extraction

Biodegradation of waste occurs in stages in a sanitary landfill, first aerobic reaction, until the depletion of oxygen, then anaerobic. In a sustainable landfill, a controlled anaerobic condition is introduced first and prevails until the majority of the biodegradable organics are exhausted. A highly efficient leachate re-circulation network is installed and instead of treating and/or disposing of the leachate, it is re-circulated back into the landfill. Because of the leachate re-circulation, the waste is maintained at optimum moisture content (50- 60%) for waste decomposition. It also serves as a medium for bacteria and nutrients transfers. Due to the rapid degradation of waste large amounts of gases are produced in a short time. This gas production will increase rapidly from early stages of operation and will attain its peak within one year. After which, the gas production will start to decrease exponentially and reach a stage where the energy recovery is not economically worthwhile to continue. A suitable gas extraction system with gauge measurement is installed for such collection and monitoring of the quantity of landfill gas released. In order to effectively implement the technology, moisture content, temperature, and gas production rate in the landfill should be monitored along with the measurement of pH and nutrients level in the leachate. Optimum microbial growth conditions depend on the presence of nutrients such as nitrogen and phosphate; and proper temperature and pH (neutral); and absence of toxic materials. Once methane production decrease to a critical value, the next stage of sustainable landfill will initiate, that is to use aerobic degradation to rapidly decompose the remaining organic waste. Since aerobic degradation rate is usually higher for simple organic compounds, this stage may take only a year or two to complete.

• Enhanced aerobic decomposition

To convert from anaerobic to aerobic conditions in the landfill, air has to be introduced to the landfill and maintained to enhance the rate of decomposition of waste (Stessel and Murphy, 1992; Hettiaratchi, 2006).The aerobic bioreactor is quite efficient, where the biodegradable waste is rapidly converted to compost like material. However, the energy content of the biodegradable waste is lost contributing to global warming. Once the landfill stop producing extractable amounts of landfill gases during the anaerobic stage of the sustainable landfill, aerobic stage is initiated to expedite waste degradation. The starting point of this stage depends on land value and cost of operating the gas extraction and the pumping systems. The gas extraction system used during the anaerobic stage will be used to pump air into the landfill to create aerobic conditions, which accelerates and completes biological degradation of organic waste. The recirculation of appropriately adjusted leachate for aerobic degradation is also required for the same reason stated in the first stage of operation. Towards the end of aerobic decomposition, periodic testing of waste composition from boreholes and the analysis of the leachate would ensure the complete biodegradation. When the organic waste is stabilized, the landfill is ready for mining.

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• Mining of useful/recyclable products

After biodegradation, mining will ensure recovery and recycling of various products (Murphy, 1993; Zee et al., 2003).At first, the whole cell is excavated. Recycling a landfill involves a series of activities that includes separating, sorting, and processing recyclables. Separation of waste based on size can be performed through the use of various types of screens (trommel, vibrating, rotating, and disc). The organics that passes through 1 cm – 5 cm sieve size can be used as compost in agricultural applications (Hudgins and March 1998). Typically the recovered material is first sieved in a 5 cm sieve shaker and then in a 1 cm sieve shaker as a second stage with 3-4 weeks of maturing before final use to enhance the quality of compost (Hudgins and March 1998). The collected non-degradable fraction will be sent to an automatic sorting unit with metal separation. A feeding belt with a magnetic drum installed on the belt is used to remove the ferrous metals. The magnetic drum can be an overhead magnet whereby ferrous metals are separated from other waste material by utilizing their magnetic properties. Light materials such as plastics and non-degraded packaging can be separated from heavy materials such as metal and glass because of their weight difference in an air stream or a cyclone.

Fig 5: Sustainable Landfill (after Hsieh et al., 2008)

• Piggyback landfill

Piggyback landfill also known as vertical expansion, is a technique used to increase the capacity of waste landfill by addition of a new cell above the existing landfill. Capacity expansion of MSW landfills in both vertical and horizontal directions has been used as a viable alternative in urban areas where land prices are rising very fast. They are primarily used to increase landfill capacity without additional land occupation. Expansion can occur by vertical and/or lateral expansion in which the old landfill is encapsulated by the new (vertical and lateral expansion), refer Fig 6, or by placement of new landfill on top of the old (piggy-back), refer Fig 7.

Fig 6: Cross Section of a Vertical and Lateral Expansion Landfill (Qian, X. 1996)

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Fig 7: Cross Section of a Piggy back Vertical Expansion Landfill (Qian, X. 1996)

• Advantages of piggyback landfill

1. Optimal use of landfill area 2. High waste volume filled per unit area 3. Low construction cost 4. Less public opposition, and 5. Easier permitting

Municipal solid waste usually settles a considerable amount during the filling operation. Municipal solid waste landfills settles approximately by 10 to 30 % of their initial height. The large settlement of the waste fill induces shear stresses in the liner system on the side slope, which tend to displace the liner downslope. The large settlement of the waste fill and the large deformation of the landfill cover tend to induce shear stresses in the final cover system. These shear stresses induce large shear displacements along specific interfaces in the liner and cover systems that may lead to the mobilization of a reduced or residual interface shear strength (Qian, 1994; Stark and Poeppel, 1994; Quian, 1996)

A landfill should be designed for long-term performance. Accordingly, landfill safety should be considered not only during the relatively brief construction and operation periods, but also during a closure period lasting potentially hundreds of years. The potential for development of other uses for closed landfills should be also considered for all side slopes for design purposes to make a landfill stable and safe even after being subjected to large settlements.

CONCLUSIONS

As developable space is becoming scarce and costly in urban areas, development on top of the landfill and adjacent to old landfills has become increasingly common. Rising prices of land and its scarcity in urban areas has created problems of waste disposal. However, with recent advancement in landfill technology such as bioreactor landfills, sustainable landfill and piggy back landfill the above issues can be tackled very well. . Bioreactor landfill is the novel method of enhancing biodegradation/settlement of the landfills by leachate recirculation. Using sustainable landfill technology, part of landfill can be converted to manure and empty space thus created can be used to take fresh waste. Developments over closed landfills has also helped to a great extent in utilisation of old and closed landfills, thus making use of landfills as potential spaces for various construction works.

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References

Bouazza, A., Kavazanjian, E., 2001. Construction on Former Landfills. Proceedings of 2nd ANZ Conference on

Environmental Geotechnics, Newcastle,467-482. Beloti, M., 2006. Personal Communication. Santa Clara University. Hettiaratchi, J., 2006. Bio-Cell Project. www.eng.ucalgary.ca/resrch_civil/bio-cell-

project/Hettiaratchi-bio-cellproject.htm. Hsieh, H., Meegoda, J., Hettiarachi, J., Haggar, S., Stressel, R., 2008. Towards the Development of

Sustainable Landfills. Proc. of Geocongress 2008: Geotechnics of Waste Management and Remediation.

Kavazanjian, E., Jr., Caldwell, J., Matasovic, N., 1998. Damage Criteria for Solid Waste Landfills. Proceedings of Sixth

U.S. NationalConference on Earthquake Engineering, Seattle, Washington. Singhal, S., Pandey, S., 2001. Solid Waste Management in India : Status and Future Directions. TERI

Information Monitor on Environment Science, (6)1:1-4. Qian, X., 1996. Design of Vertical Landfill Expansions. Michigan Department of Environmental

Quality, Waste Management Division, Lansing, MI. Walsh P., O’leary, P., 2002. Landfill Bioreactor Design and Operation. Waste Age, June, 72-76. Wilson, D. G., 1977. The History of Solid Waste Management. Handbook of Solid Waste Management,

Ed. D G Wilson, New York, Van Nostrand Reinhold.

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EFFECTS OF CHEMICAL ADMIXTURE ON SETTING AND STRENGTH PROPERTIES OF

FAL-G BLOCKS

S. P. Singh, J. K Naik and S.Tripathy Department of Civil Engineering, National Institute of Technology, Rourkela-769008, Odisha, India

Abstract: The paper reports the experimental results on the effects of chemical admixtures on setting and strength properties of FAL-G blocks. Fly ash of the captive power plant of Indian Aluminum Company, Hirakud was used in the test program. Calcium chloride and sodium carbonate are used as chemical accelerators. The initial setting time (IST), final setting time (FST) and the compressive strength of mixture of fly ash-lime-gypsum added with different doses of chemical admixtures were evaluated. Addition of chemical accelerator like sodium carbonate and calcium chloride to a mix of fly ash–lime–gypsum decreases both IST and FST values. It is observed that there exist an optimum amount of chemical accelerators which results a higher early strength gain as well as higher ultimate strength. A dose more than the optimum amount, is detrimental for the strength. The compressive strength of FaL-G blocks decreases upon saturation. The soaked strength is found to be about 70 to 80% of unsoaked strength.

INTRODUCTION

Fly ash is a by-product of thermal power plants, collected by mechanical or electrostatic separators from the flue gases of power plants. It is very fine material consisting predominantly of small spheres of glass. It is estimated that the generation of fly ash from coal fired generation units in India will reach 170 million tons by 2012 and increases up to 225 million tons by the end of year 2017. At present in India, only about 35% of the generated fly ash finds its use in commercial applications. However, in some developed countries utilization is as high as 70 to 100 percent. Large scale utilization of fly ash in construction industry as a replacement to the conventional materials will solve two problems with one effect, i.e. in one hand elimination of solid waste problem and in other hand provision of needed construction material.

Brick is an age old construction material which consumes the bulk of cost of construction. India needs about 60 billion of bricks every year which would exhaust 160 million tons of top soil making barren 3 thousands hectors of fertile land. Now a days search is being made to utilize industrial wastes in construction industry as an alternate to conventional materials. As fly ash is rich in reactive silica and alumina, it undergoes pozzolanic reaction with lime and/or gypsum. This technology is used in manufacture of FaLG bricks or blocks. Fly ash blocks offer a sustainable eco-friendly alternative material for building in both developed and developing countries. However, the manufacturers of fly ash bricks face some social and technical problems that are yet to be solved. Few such problems faced by the brick manufacturers are the slow rate of strength gain, low ultimate compressive strength, and high water absorption capacity of blocks. This decreases the acceptability of the brick by the end users. To overcome these problems, an attempt has been made to accelerate the setting and hardening of FaL-G blocks by using chemical admixtures. Calcium chloride and sodium carbonate are used as chemical accelerators in this testing program. The initial setting time (IST), final setting time (FST) and the compressive

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strength of mixture of fly ash-lime-gypsum added with different doses of chemical admixtures were evaluated. It is the one of the innovative use of industrial waste products.

EXPERIMENTAL PROGRAMME AND METHODOLOGY

• Raw Materials

In the present investigation, FaL-G blocks were prepared from fly ash, lime, gypsum and sand. The fly ash was collected from captive power plant of India Aluminum Company (INDAL), Hirakud. Lime and gypsum were procured from the local market. Sand was collected from the nearest river. The fraction of sand passing through 2 mm sieve and retained on 425micron sieve was used in the present study. These raw materials were processed and kept in airtight container for further use. The physical properties of the fly ash and sand are given in Table 1.

Table 1 Physical Property of Raw Materials

Physical parameters Fly ash Sand Colour Grey Wheatish Shape Rounded Sub- rounded to angular Specific gravity 2.41 2.63 Plasticity index NP NP

Grain size distribution (%) Silt & Clay 98 0 Fine sand 02 0 Medium sand 0 100 Coarse sand 0 0 Uniformity coefficient 4.88 2.36 Coefficient of curvature 1.45 0.895

• Determination of IST and FST

The setting time of different mixes of fly ash-lime-gypsum with chemical admixtures are determined as per IS: 4031 (Part-V) 1988. In the first series of tests the initial and final setting time of the mixture of fly ash-lime-gypsum were determined by keeping lime at 8% and gypsum 6%. In the second series of tests the setting time of different mixes were determined by adding chemical accelerators like CaCl2 and Na2Co3. The amount of chemicals in the mixtures was varied as 0, 2.5, 5, 10 or 15% of the weight of lime added, whereas the gypsum content is fixed at 6 percent. For all these tests the raw materials and chemicals were mixed thoroughly in dry condition and then 0.65 times of water that is required for the normal consistency, was added and the paste were prepared. The initial and final setting times were determined by using Vicat apparatus. The test results are presented in Table 2.

• Determination of compressive strength and water absorption

For determination of compressive strength, fly ash and sand was mixed in 40:60 proportions. The amount of lime and gypsum in the mix were taken as 8% and 6% of the dry mass of fly ash used. This proportion of the raw material was fixed as per the earlier work of Dhar, P. K (2005), which gave the optimum compressive strength. Chemical accelerators like CaCl2 and Na2Co3 were added to this mixture. The amount of chemicals in the mixtures was varied as 0, 2.5, 5, 10 or 15% of the weight of lime. In dry condition the raw materials were blended thoroughly. The amount of

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water close to OMC was added to give proper consistency to the mixture for easy moulding. A moulding pressure of 100kg/cm2 is used to prepare the blocks. The green samples were cured under controlled temperature of 400C and relative humidity of 80% in humidity chamber. The blocks were of size of 70.5mm×70.5mm×50mm. The compressive strength of the blocks was determined after curing periods of 0, 1, 3, 7, 14 and 28days. Three samples were tested for determining the compressive strength for each testing condition. Similarly, the water absorption of the cured blocks was determined by soaking the dry blocks in water for three days with respect to its dry weight and is given in Table 3 & Table 4.

Table 2 Setting times of fly ash-lime-gypsum mixes added with chemical admixtures

Admixture Na2Co3 CaCl2 IST (in hours) FST (in hours) IST (in hours) FST (in

hours) 0 2.75 26.5 2.75 26.5 2.5 2.75 9.5 3.5 17 5 2.5 8.75 3.5 13.5 10 2.25 8.5 3.25 13 15 2 7.5 3 7.75

Table 3 Compressive Strength and water absorption of FaL-G blocks added with calcium chloride

CaCl2 (%) Compressive Strength (kg/cm2) Water

absorption (%)

0 hr 1 day 3 days 7 days 14 days 28 days

0 8 22 84 104 116 128 20.87 2.5 8.5 23 92 126 140 144 20.77 5 9 25 106 144 156 160 19.81 10 9.5 27 132 160 168 180 18.47 15 7 24 120 148 160 172 18.97

Table 4 Compressive Strength and water absorption of FaL-G blocks added with sodium carbonate

Na2Co3 (%) Compressive Strength (kg/cm2) Water

absorption (%)

0 hr 1 day 3 days 7 days 14 days 28 days

0 8 22 84 104 116 128 20.87 2.5 8.5 24 96 124 144 156 15.78 5 9.5 26 116 140 156 168 14.73 10 10 34 136 156 168 177 14.28 15 8 31 128 142 152 160 18.74

RESULTS AND DISCUSSIONS

• Effect of chemical admixtures on IST and FST

It is found that an increase in sodium carbonate content does not change the IST value. However the FST value decreases drastically with addition of sodium carbonate. The maximum decrease in FST value is observed when the amount of sodium carbonate is increased from 0 to 2.5%. Thereafte,r the decrease is not that prominent. When sodium carbonate percentage increased

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from 0 to 15 % the IST and FST value changed from 2 hours 45 minutes to 2 hours and 26 hours 30 minutes to 7 hour 30 minutes respectively. Similarly the FST value is found to decrease drastically with addition of calcium chloride. Initially the rate of decrease is high then there is a mild decrease. The addition of sodium carbonate and calcium chloride to the mix of fly ash-lime increases the concentration of Na+ and Ca++ cations. Both IST and FST values decrease due to the cationic action of Na+ and Ca++ which helpful in accelerating the forward reaction of gel formation. The Cl- and CO3

-- anions released in the process, reacts with water forming hydrochloric and carbolic acids. The strength of these acids depends on the concentration of the above anions and hence the amount of chemical accelerators added. High dose of the above chemicals produces a strong acid which retards the gel formation. Hence from the present investigation it can be concluded that addition of small amount of above chemical accelerators (2.5 % of lime) are certainly advantageous in accelerating the chemical reaction, and hence reducing the setting time of the mixtures.

• Effect of chemical admixtures on compressive strength and water absorption

The effects of chemical accelerators like calcium chloride and sodium carbonate on the compressive strength was determined by adding different amount of chemicals (0 to 15 %) to a mixture of fly ash, sand, lime and gypsum. Samples were prepared with moulding pressure of 100 kg/cm2. Fig 1 and Fig 2 show the variation of compressive strength with calcium chloride and sodium carbonate. It is found that compressive strength for all days of curing increases with the chemical accelerator up to 10 %, thereafter the same decreases. Addition of chemical accelerators accelerates the pozolanic reaction due to high concentration of Na+ and Ca++ cations. However the pozolanic reaction requires an ambient pH value at which the rate of reaction and strength gain is maximum. The anions (Cl- and CO3

--) released from the chemicals form weak acids, the strength of which depends on the amount of chemical added. A higher dose of chemical is responsible for formation of comparatively acids of higher strength which changes the pH value and hence the rate of pozzolanic reaction. It is also concluded that optimum amount of chemical accelerators give early strength gain as well as high ultimate strength. A dose more than the optimum amount is detrimental for strength. Fig.3 shows the variation of water absorption with the amount of admixtures. The water absorption directly measures the void space in the cured blocks. As the amount of chemicals increased, more and more insoluble gels are formed which occupies the void space, reducing the percentage of water absorption. Beyond a certain dose of chemicals the gel formation reduces. As the formation of insoluble gel is directly related to the void space so that the water absorption increases beyond this optimum dose of chemical.

Fig 1 Variation of compressive strength with calcium chloride

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Fig 2 Variation of compressive strength with sodium carbonate

Fig 3 Variation of water absorption with the amount of admixture

CONCLUSIONS

Fly ash is more or less a well graded material having co-efficient of uniformity is 4.88 and co-efficient of curvature 1.45. Specific gravity of fly ash is 2.41 which are slightly less than that of similar graded conventional earth material. Addition of chemical admixture like sodium carbonate and calcium chloride to a mix of fly ash- lime- gypsum results in decrease of both initial setting time (IST) and final setting time (FST) values. The maximum decrease in FST value occurred with 2.5 % chemicals. Compressive strength is found to be increased with the addition of sodium carbonate and calcium chloride up to 10 % thereafter, the same decreases. It is found that; at optimum amount of chemical admixture exists that result in early gain of strength as well as higher ultimate strength. A dose more than optimum amount is detrimental for the strength. Based on the experimental work it is found that the setting and strength behavior of FaL-G blocks can be improved by adding an optimum dose of chemical admixture. The utilization of fly ash in manufacturing of bricks will solve two problems with one effort such as elimination of solid waste and provision of a much needed construction material.

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References

Dhar, P. K. (2005) “Effect of chemical accelerators on setting and strength characteristics of FaL-G Blocks” M. Tech. thesis submitted to National Institute of Technology, Rourkela, Odisha, India

Reddy, V., Rao, Sudhakar, M.B.V & Kumar, M. K. A. (2003)”Characteristics of Stabilized mud blocks using ash modified soils’’. The Indian concrete journal, PP 903-911.

Singh, M. (2002), “Value added products from industrial wastes”.CE & CR February, PP 35-43 Singh, S.P., & Tripathy, D.P. (2001),”assessment of the suitability of flyash in geotechnical

construction”.I E(I) Journal-CV, Vol. 82, August. PP 77-80. Natesan, S. C., Kumar, Ananda, S., & Babu D. L., Venkatesh, (2001), “Effect of pulverized fuel ash

(PFA) & condensed silica fume (CSF) on the strength of high performance concrete” (HPC), International Conference on civil Engineering, Bangalore,

Singh, S. P. & Panda, AP. (1996), “Utilization of fly ash in Geotechnical Construction”, Indian Geotechnical Conference, December, 11-14, Madras.

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CONSTRUCTION AND ENVIRONMENTAL ISSUES

Ramandeep Kaur1, Sarpreet Singh2 and Manpreet Singh3

1Department of Chemistry, S.U.S. Govt. College, Sunam-148028, Distt. Sangrur 2Department of Computer Science and Engineering, Sri Guru Granth Sahib World University,

Fatehgarh Sahib 3Department of Computer Science, Akal Degree College, Mastuana Sahib, Sangrur

Abstract: Environment means a circumstance or conditions that surround one or the other. In short, it means surroundings, Societal and physical. It is a combination of external physical conditions that affect and influence the growth, development, and survival of organisms and the complex of social and cultural conditions affecting the nature of an individual or community – poverty, geography, and access to clean water, air, and health care facilities. Keeping this in view, the issues of environment are always need to be discussed. Among a variety of these issues, the issues which we want to share are Construction, Sustainable development and Indoor Life Quality. Besides this, the most surprising factor which counts in the list of exploiting environment is divorce, too. In other words, this paper considers some of the challenges, which can be removed by proper planning.

Keywords: Environment, Construction, Sustainable development, Indoor Life Quality, Divorce

INTRODUCTION

Each and every living being needs healthy environment to survive. ‘Healthy environment’ means the environment which provides oxygen to breathe, water to drink and food to eat but all of this with purity. In the present era of technological advancements, ‘Healthy environment is becoming a dream for everyone. This might be due to the reason that we are disturbing nature by our self-centered deeds. Scientists give 4 major reasons for this imbalance: Rapid increase in population, Urbanisation, Industrialisation and Agricultural practices. We’ve forgotten a saying that “We do not inherit the earth from our ancestors; we borrow it from our children”. There are three basic needs of a human being ‘Roti, Kapadha aur Makaan’. But, due to fast growing population, he/she feel shortage of these three necessities. In the present paper, we are discussing only about ‘Makaan’. The main aim of this paper is to put forth the environmental issues through another angle, i.e.through construction factor . Illegal encroachments, illegal construction etc. are creating big chaos in the world rather, in the developing countries. Increasing population results in the rapid loss of land is due to:

• Real estate as an investment. • Difficulty in agriculture on the reasons of labour, not getting minimum price, high cost of

inputs etc. • Socio economic reasons like loss of joint family system and development of separate

families.

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• Loss of traditional family business and development of master - servant system after the british invasion.

• Other development works without planning the future population and scientific advancements.

• Politics.

Unless all these are addressed, no solution is possible for the deteriorating conditions of the cities. The developing countries give a picture of piles of garbage and glitzy new shopping malls. Is this our vision of urban development? Cities are imploding, growth is happening faster than we ever imagined. Construction is booming and expansion is gobbling agricultural land. ‘We never know the worth of water till the well is dry’. Thomas Fuller, Gnomologia, 1732. To obtain "sustainability" and "sustainable development" many features, mainly in developing countrieures should be kept in mind.

• The objective is to sustain the species homosapiens. That is to support it and keep it alive. • Sustainability is the condition or state which would allow the continued existence of

homosapiens, and provide a safe, healthy and productive life in harmony with nature and local cultural and spiritual values. It is the goal we would like to achieve.

• Sustainable development is then the kind ofdevelopment we need to pursue in order to achieve the state of sustainability. It is acontinuous process of maintaining adynamic balance between the demands of people for equity, prosperity and quality of life, and what is ecologically possible. It is what we need to do.

• Urban sustainability is the broader process of creating sustainable human settlements, especially towns and cities. It includes sustainable construction, but also the creation of institutional, social and economic systems that support sustainable development.

• Sustainable construction means that the principles of sustainable development are applied to the comprehensive construction cycle from the extraction and beneficiation of raw materials, through the planning, design and construction of buildings and infrastructure, until their final deconstruction and management of the resultant waste. It is a holistic process aiming to restore and maintain harmony between the natural and built environments, while creating settlements that affirm human dignity and encourage economic equity. "Sustainable development is development that meets the needs of the present without compromising the ability of future generations to meet their own needs. As such it requires the promotion of values that encourage consumption standards that are within the bounds of the ecologically possible and to which all could reasonably aspire."

Source: Our Common Future, WCED, 1987

• Green and Brown Agendas

These terms which explains the concerns of the North and those of the South, and is expressed in terms of the Brown and Green Agendas The "Brown" and "Green" agendas. The Green Agenda concentrates on reducing the environmental impact of urban-based production, consumption and waste-generation on natural resources and ecosystems, and ultimately on the

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world’s life-support systems. In general, the Green Agenda, which focuses on the problems of over-consumption, is more pressing in affluent countries. The Brown Agenda, which focuses on the problems of poverty and underdevelopment, emphasizes the need to reduce the environmental threats to health that arise from poor sanitary conditions, crowding ,inadequate water provision, hazardous air and water pollution, and local accumulations of solid waste. Source: agenda 21 for sustainable construction in developing countries, a discussion document (the International Council

for research and innovation in building and construction CIB and United Nations Environment Programme International Environmental Technology Centre UNEP-IETC)

The clearing of lands for construction can lead to the loss of wildlife habitats, erosion and sedimentation associated with the use of heavy machinery, loss of native plant life, and contamination of soils and surface and groundwater. “What we are doing to the forests of the world is but a mirror reflection of what we are doing to ourselves and to one another.” –Mahatma Gandhi. However, proper design and planning can help reduce these impacts.

Moreover, Wastes associated with building/housing construction include unused and excess material generated during site excavation, site clearance, construction, and renovation activities. These wastes may be rubble (concrete, bricks, and asphalt), wood and wood products, plaster, metals, plastics, and insulation. Further, some of these waste products may contain toxic constituents that pose a risk to human health and the environment. Many local governments have passed ordinances that restrict or prohibit the disposal of debris in landfills and require the recycling of many of these materials. In addition, purchasing decisions associated with building/housing construction projects can affect the amounts of waste generated, as well future energy requirements (e.g., from lighting and heating). Sustainable or “green building” design and construction is the opportunity to use our resources more efficiently, while creating healthier and more energy-efficient homes. In other words, green building design involves finding the delicate balance between homebuilding and the sustainable environment.

Favorable environment in the house includes good indoor life quality. Indoor Life Quality and Indoor Air Quality (IAQ) are important phrases in today’s lexicon, used by both the building industry and the general public. However, many people fail to recognize the importance of a systems approach and green building design in improving Indoor Life Quality and IAQ. Indoor allergen agents—from dust mites and cockroaches to fungi, mold, dander, hair, saliva, viruses, bacteria, spores, secondhand tobacco smoke, pesticides and other materials—contribute to poor IAQ. Water vapor also is a major contributor to IAQ as moisture build-up can cause deterioration of building materials, structural damage, and can help create an environment for bugs, mold, and rot. If used appropriately, plastic can be an effective and continuous air and vapor retarder to keep the water vapor entering the home envelope to a minimum. A combination of effective air and vapor barriers allows the ventilation system to work efficiently and provides a means to control the condition of the air entering and exiting a home. Solid vinyl or vinyl-clad window frames can be another part of the solution. They not only reduce heat loss, but also minimize condensation.

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Following is the list of some indoor pollutants, showing their bad effects:

POLLUTANT MAIN SOURCE EFFECT

Tobacco smoke Cigarettes, cigars & pipes Respiratory, heart diseases& Lung cancer

CO Gas, wood stove Coal stove

Fatal, headache nausea, angina

Nitrogen oxides Malfunctioning Gas appliances Eye, nose, throat irritation, res. inf.

Organic chemicals Aerosol sprays, glues, paints, moth repellents--

ENT. liver, brain kidney damage Various cancer

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Formaldehyde Plywood, board, wallpaper, press fabric, furnishings

ENT irritation, headache, allergy cancer

Inhale able particles

House dust, aerosols, smoke ENT, respiratory inf., Lung cancer

Biological agents- bacteria, viruses, fungi, dander, mite

Dust, pets, beddings, air conditioners, wet structures

Allergy, asthma, ENT, fever, influenza, inf. diseases

Asbestos Damaged insulation, fireproofing Asbestosis, various cancers ,

Lead Lead paints, dust, Cosmetics

Growing Brain& kidney damage, anemia, allergy

Radon Soil , old houses, ground water Nervous damage, lung cancer

Not living in fresh environment results in dizziness, headaches, eyes irritated, nasal discharge, sore throat, coughing, nausea and vomiting, shortness of breath, airway constricted, chest pain, poison in blood stream, poison swallowed into stomach.

The U.S. government environment protection agency (EPA) and its science advisory board (SAB) have consistently ranked indoor air pollution among the top five environmental risks to public health. WHO – reports that in 23 countries 10% deaths are due to just two risk factors: unsafe water, including poor sanitation & hygiene; and indoor air pollution due to solid fuel use to cook? WHO reports that nearly 70% of rural households in India don’t have ventilation. There is a need to raise awareness and schemes of WHO that has target proper ventilation and relaunch of smokeless chulha that can reduce death rate to half by 2015 in India.

In developing countries, consideration for environmental conservation often receives a low priority, while approaches used in industrialized countries often cannot be applied directly in developing countries. Due to the increased energy consumption, developing countries will account for over 3/4 of the increase in global CO2 emissions between 2004-2030. Similarly the share of developing countries in world greenhouse gas emissions will rise from 39% at present to 52% by 2030. For example, in China, coal currently accounts for about two-thirds of China's total energy usage and is responsible for fuelling 70-80% of power generation, 75% of energy used in industry, and even 80% of household energy, causing major environmental degradation in China. Similarly in India, the major sources of air pollution in the urban and industrial areas are industrial processes (40%), transportation (25%), fuel production (25%), others (10%).

Recently, a session judge from New Delhi’s has addressed some astonishing facts. According to her, the global trend towards higher divorce rate has created more households with fewer people. More households mean more energy expended to build, towards fuel and to provide water for them, thereby contributing to global warming. Whether there are 2 or 3 or 6 people in a house, the amount of fuel needed for heating is about the same. Even in regions with a declining population, there is a substantial increase in the no. of households. She advice litigants in the divorce cases: ‘Try to save marriage as this will save your energy and other resources. Promote love for better utilization of national income.’ Source: The Tribune/ 25.12.12

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CONCLUDING REMARKS

• It should be properly checked that the construction project is really necessary? Is the project over-designed? In some cases, the construction of additional structures is not needed and minor alterations to existing facilities may be sufficient.

• Have attempts been made to avoid construction in environmentally sensitive areas (such as wetlands and threatened or endangered species habitats).

• The specifications for construction practices should be designed to control and exclude pest entry in contained habitats?

• the construction contract specify that contractors should cause the least possible disturbance to the site's vegetation. For example, under certain circumstances, it may be possible to preserve individual trees or stands of old growth that would otherwise be destroyed.

• The construction plan must include the provision for erosion and sediment control Uncontrolled soil erosion can have adverse effects on local water bodies and aquatic life.

• The soil excavated from the construction site must be reused. Topsoil can be re-spread in areas to be landscaped to enhance plant health.

• The plan must include the re-vegetation of areas disturbed by construction. • There is a plan to reduce the use of materials containing constituents that can negatively

affect the environment. • The home is properly ventilated, with at least exhaust fans in the bathroom and kitchen

and ventilation system designed to ventilate the entire house • Proper domestic garbage and sewage disposal and recycling can transfer pollutant to

biogas, farm resource-‘black gold’ • So, it is up to us that how much importance we give to “Environment” in which we live. • Remember, “PROFIT IS OF INDIVIDUAL BUT DEPLETION OF RESOURCES

IS OF EVERYBODY”

“Let us join hands together to save Our Mother Earth”

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FaL-G: AN ALTERNATE BUILDING MATERIAL

Sanjeev Naval, Sagar Tandon, Pankaj Maini, Nishita Sharma and Uday Pratap Srivastav

Department of Civil Engineering, DAV Institute of Engineering & Technology, Jalandhar

Abstract: In this paper an effort has been made to find an alternative to clay bricks using fly ash, lime and gypsum. A series of laboratory cube tests have been carried out to investigate the effect of various proportions of lime, fly ash and gypsum on the strength characteristics of FaL-G cubes. In this study 50%, 60%, 70% & 80% of fly ash was mixed with various proportions of lime and gypsum by weight, having water content equal to consistency. These cubes were tested after 7 and 28 days on Compression Testing Machine. It was observed that the best proportion of fly ash, lime and gypsum was 80%, 10% and 10% respectively, having a compressive strength of 2.2N/mm2 and 6.54N/mm2 after 7 and 28 days respectively.

INTRODUCTION

FaL-G is the Technological Renaissance of cement chemistry, taking clue from the ancient Roman construction technologies. Bhanumathidas and Kalidas(1993), emerged out of national agenda for promoting fly ash utilization of over 63 million tons. Bhanumathidas and Kalidas,(1999), Fly ash-based brick and cement are far superior inengineering properties over their conventional competitors.This knowledge needs to be disseminated globally, more soin second and third world countries, through tangible technical explanations. The opportunity to abate CO2 is 35 million tonnes in cement and 45 million tons in brick by using fly ash in boththe segments in India. Amit Mittal et.al(2003), conducted testes on concrete mixes with 300 to 500 Kg/m3 cementitious material at 20% , 30% , 40 % and 50% replacement levels the effect of fly-ash on workability, setting time, density, air content, compressive strength, modulus of elasticity, shrinkage and permeability of rapid chloride permeability test (RCPT) are studied. According to INSWAREB(2005), In fly ash-lime (FaL) mixes, the strengths are mainly from calcium silicate hydrates (CSH). In the case of fly ash-lime-gypsum (FaL-G) mixes, the early strengths are imparted by calcium alumino-sulphate hydrates (CASH) supplemented by CSH for late-age and ultimate strengths. As a result, the strengths of FaL in the range of 60-80-120 kg/cm2 get boosted to 200-250-350 kg/cm2 as FaL-G. Bhanumathidas and Kalidas(2004) stated that the rapid hydration of calcium aluminates to form calcium aluminate hydrate (CAH) hampers the hydration of calcium silicate. As shown in following chemical reaction, in the absence of gypsum

3 CaO. Al2O3 + nH2O fast reactions ⎯⎯⎯⎯⎯⎯⎯⎯⎯CAH + profuse exothermic heat

Hence, it was found essential to change the reaction course of C3A, and this was met by the use of sulphate salts. Due to its affinity with SO3 , aluminate tends to react readily with the former and in this process the reactions of aluminate with water are prevented. Ultimately, gypsum was identified as the most effective form of sulphate to control hydration reactions of C3A that incidentally resulted in early strength gain and better workability for a longer duration. Chemical reaction in the presence of gypsum is given below

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3CaO.Al2O3 + 3CaSO4.2H2O + nH2O ⎯⎯⎯⎯⎯⎯⎯⎯ 3CaO.Al2O3.3CaSO4.32H2O

(Ettringite : calcium trisulpho aluminate hydrate) + moderate exothermic heat DEGIRMENCI and OKUCU (2006) stated that the water absorption and thermal conductivity of the specimens increases with the increase in phosphogypsum content. Also the increase in the amount of phosphogypsum addition caused a reduction in the dry unit weight of the specimens. The test results show that these binders may be utilized in production of construction elements such as blocks, masonry mortars and controlled low-strength materials. Bentz et. al.(2011), characterized the thermal properties namely, specific heat capacity and thermal conductivity of concrete mixtures in which the Portland cement was replaced by 50% or more of fly ash. Both the raw material and the finished products were evaluated using the transient plane source method.

EXPERIMENTAL INVESTIGATION

• Materials

Fly ash obtained from Thermal Power Plant located at Bathinda, Punjab was used in this study having properties as shown in Table 1. Gypsum and Lime were obtained from local market.

Table 1: Various properties of fly ash

Properties Values

Density 2.23

Specific Gravity 2.06

Moisture Content 0.01%

• Mix proportions

Four mixture proportions were made. In all mix proportions content of lime is kept constant as 10%. Different proportion of fly ash was taken as 50%, 60% 70% and 80% and remaining proportion of gypsumwas simultaneously added. All ingredients were uniformly mixed in dry state. After mixing the ingredients water content equal to consistency as shown in Table 2 was added.

Table 2: Consistency, Initial Setting Time and Final Setting Time of FaL-G mixture at different proportion of Fly ash, Lime and Gypsum

MIX PROPORTIONS(%) CONSISTENCY

(%)

Initial Setting Time (min)

Final Setting Time (min)

Fly ash Lime Gypsum

50 10 40 59 3 4.5 60 10 30 58 3.5 5 70 10 20 57 4.5 6.5 80 10 10 57.5 5 7

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CASTING AND TESTING OF SPECIMENS

The 7.07cm cubes were used, after casting all the test specimens are finished with a trowel. Figure 1 shows casted test specimens of Fal-G Cubes. Six specimens of each proportion are mixed. Moulds were kept on vibrator and pouring is done. All the test specimens are stored at temperature of about 30o C in the casting room. They are demoulded after 24 hours, and water sprinkling is done 2 times in 24 hours. Compressive strength at 7th day and 28th day was found using Compression Testing Machine as shown in Figure 2.

RESULTS AND DISCUSSION

Table 3 shows the values of compressive strength of FaL-G cubes at having different percentages of fly ash and gypsum having 10% lime content tested at 7 and 28 day, the quantitative representation of same has been shown in Figure 3. Figure 4 shows curves representing compressive strength of cubes with increase in the gypsum proportion and Figure 5 shows curves representing compressive strength of cubes with increase in fly ash proportion at 7 and 28 day. Figure 6 shows curves representing change in compressive strength of cubes with time at different percentages of fly ash and gypsum.

Table 3: Compressive Strength of Fal-G cubes at different proportion of Fly ash, Lime and Gypsum

MIX PROPORTIONS (%) Compressive Strength

Fly ash Lime Gypsum 7 day (in N/mm2) 28day(in N/mm2)

50 10 40 0.43 1.6

60 10 30 1.00 3.7

70 10 20 1.65 5.3

80 10 10 2.2 6.54

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Fig 1: Fal-G cubes

Fig 2: Compression testing of Cubes

Fig 3: Compressive strength of FaL-G cubes for different proportion of Fly ash and gypsum at different days of testing

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Fig 4: Compressive strength of FaL-G cubes at different percentages of fly ash at 7th and 28th day

Fig 5: Compressive strength of FaL-G cubes at different percentages of Gypsum at 7th and 28th day

Fig 6: Compressive strength of FaL-G cubes at 7 and 28 day for different proportions Fly ash and Gypsum

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A minimum compressive strength of 1.6N/mm2was achieved using 50% fly ash, 10% lime and 40% gypsum and a maximum compressive strength of 6.54N/mm2 was achieved using 80% fly ash, 10% lime and 10% gypsum as shown in Table 2 and Figure 3. According to Figure 4, strength of cubes is directly proportional to percentage of fly ash in them hence fly ash is playing major contribution in strength. It has been observed in Figure 5 that with an increase in the percentage of gypsum at constant percentage of lime compressive strength at 7 and 28th day is found to be decreased which is against the statement that gypsum provide early strength and increases workability for longer time, this may be due to the reason that the formation of ettringite at threshold levels accelerates the hardening process and thus reduces strength gain at early ages. As shown in Figure 6 the slope of the graphs decreases with increase in percentage of gypsum, hence it proves that utilization of fly ash takes lesser time with higher percentage of gypsum.

CONCLUSIONS

• Most of the contribution in strength of cubes is due to fly ash. • A maximum compressive strength of 6.54N/mm2 at 28 days has been observed with a mix

having 80% fly ash. • Absence of burning and heavy compaction during manufacturing of FaL-G bricks saves

energy, cost and makes it environment friendly hence it could be implemented as an alternative to clay bricks.

References

Amit Mittal , M. B. Kaisare, Rajendra kumar Shetti(2003), “Experimental study on use fly ash in concrete” Nuclear Power Corporation of India Limited.

Bhanumathidas, N., Kalidas, N.(1993). “The Renaissance of Mediaeval Age Cement: FaL-G.” Civil Engineering & Construction Review, 31-33.

Bhanumathidas, N., Kalidas, N.(1999). “The Rationale for Portland Pozzolan Cement Compositions” Proceedings of International Conference on ‘Waste and By products as Secondary Resources for Building Materials.

Bhanumathidas, N., Kalidas, N.(2004). “Dual role of gypsum: set retarder and strength accelerator” The Indian Concrete Journal,78 , 3, 170-178. INSWAREB (2005). “A Case Example of a Programmatic Small-Scale CDM Project: The FaL-G Brick

Project in India“ Institute of solid waste research & Ecological Balance. Nurhayat DEĞIRMENCI, Arzu OKUCU(2006). “Usability of fly ash and phosphogypsum in manufacturing of building products” Journal Of Engineering Sciences, Sayfa, 2, 273-278. DP Bentz, MA Peltz, A Dura´n-Herrera, P Valdez, CA Jua´rez(2011) “Thermal properties of high-

volume fly ash mortars and concretes” Journal of Building Physics, 34(3), 263–275.

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IMPROVEMENT OF SUB-GRADE USING QUARRY DUST WASTE

Prashant Garg1 and Gurcharan Singh2 1Department of Civil Engineering, Guru Nanak Dev Engineering College, Ludhiana 2Department of Civil Engineering, Guru Nanak Dev Polytechnic College, Ludhiana

ABSTRACT: Soil is defined as a natural aggregate of mineral, loose or moderately cohesive, in-organic in nature that has the capacity of being separated by means of simple mechanical process by agitation in water. Generally strength of soil improves by compaction but in some cases strength even after compaction may not be adequate and processes of soil stabilization, reinforcing sheets, strips, bars, grids of fiber, coir etc of the soil is to be adopted. In present study, the engineering properties of soil is try to improve by introduction of quarry waste i.e. stone dust and coir fibers in the local soil in different percentage and a comparative study is made to find out the best combination of stone dust and coir in view to economize the flexible Pavement construction. To achieve this objective a number of C.B.R. test were conducted on the local soil along with different percentage of stone dust and coir with varying aspect ratio. It is concluded that the construction of flexible pavement may be economize by using 60% of stone dust and 2.25% of coir with aspect ratio as 100.

INTRODUCTION

The production of aggregates from crushed rock generates a proportion of fines as normal consequence of variable responses of the rock material to the crushing process. A number of strategies have been developed to make use of fines, in accordance with the need of local markets, regulation and legislation. Quarry waste, stone dust is also such a material which is a byproduct of Stone crusher and is considered as a waste which is creating environment problems and Government of India has initiated many research project to utilize this waste like Fly-ash. In the present study the engineering properties of stone dust was investigated and recommendations regarding how this dust can be used to improve the strength characteristics of the sub grade soil. Quarry dust was mixed with the local soil in different proportions and tests were conducted. an optimum mix of the sample was arrived at based on the compaction characteristics, CBR value in both soaked and unsoaked conditions. In study the effects of randomly fiber reinforcement on CBR values of sub grade soil were also observed to find out optimum mix of soil, stone dust and coir.

EXPERIMENTAL PROGRAMME

Following experiments were performed on local soil, stone dust and combinations of soil, stone dust and coir into different proportion as per Indian Standard guidelines to find out their Physical and Engineering properties:

• Pycnometer test for specific gravity • Liquid limit test • Plastic limit test

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• Standard Proctor Compaction test • California Bearing Ratio test

MATERIALS

• Soil

Soil is obtained from the Campus of Guru Nanak Dev Engineering College, Ludhiana. According to Indian Standard of Soil Classification, the soil was found to be inorganic clay of low compressibility. The Plastic Index lies in between 4 – 7. The engineering properties are given in Table 1.

Table 1: Properties of Soil used

1 Colour Light Brown 2 Liquid limit % 22 3 Plastic Limit % 18 4 Plastic index % 4 5 Specific Gravity 2.65 6 Max. Dry Density KN/m3 16.9 7 O.M.C % 16 8 I.S. Classification ML/OL 9 CBR % unsoaked 8.4 10 C B R % soaked 6.7 11 Grain size Distribution

Sand (.075-4.75mm) % Silt (.002-.075mm) % Clay (<.002mm) %

72 25 03

• Coir Fiber

The coir was purchased from the market. It is fibrous portion of the coconut extracted mainly from the green nut. Coir extracted consists of rotting the husk in water and removing the organic material binding the fiber. The coir was cut into the pieces of required length, so that aspect ratio remains 50, 75, and 100. Other dimensions of coir are given below:

1 Length 25mm, 37.5mm, 50mm 2 Diameter 0.5mm 3 Price Rs. 50 /- per Kg

• Water

Ordinary potable water from tap was used for the study. Water was clean, neat and without any suspended material.

• Stone Dust

Stone dust was procured from the nearby Quarry mainly from Panchkula near Chandigarh. It is by product of the stone crushers and is available free of cost. The Physical and Engineering properties of stone dust used in experimentation is given in Table 2.

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Table 2: Properties of Stone Dust

S. no. Properties Stone dust

1 Grain Size Distribution Sand (.075-4.75mm) % Silt (.002-.075mm) % Clay (<.002mm) %

83 16 0.0

2 Standard Proctor Compaction OMC % Max. dry density KN/m3

13.0 19.5

3 Specific Gravity 2.80 4 Liquid limit % 19

RESULTS AND DISCUSSION

Standard Proctor Compaction Test were conducted on soil and stone dust with different proportion as 0, 20, 40, 60, 80, 100%. The result is shown in Table 3.

Table 3: Results of SPC Test

Soil Mix (Soil : Stone Dust)

Designation MDD (γd)max KN/m3

OMC (%)

100:0 S0 17.8 16 80:20 S20 18.5 15.2 60:40 S40 19.0 14.6 40:60 S60 20.2 11.8 20:80 S80 19.9 12.4 0:100 S100 19.5 13

CBR test were also performed in the laboratory and CBR values of the sample is shown in

Fig. 1. And the summary of various samples is tabulated in Table 4.

Fig 1: CBR value of various samples

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Table 4: Various results for samples

Legend MDD KN/m3

OMC %

CBR unsoaked

% increase CBR soaked

% increase

S0 17.8 16 8.4 6.7 S20 18.5 15.2 9.2 9.5 7.51 12.8 S40 19.0 14.6 10.4 23.8 14.3 8.34 24.5 16.7 S60 20.2 11.8 13.5 60.71 36.91 10.9 62.9 34 S80 19.9 12.4 15.7 86.9 26.91 12.2 8.2 19.1 S100 19.5 13.0 22.61 18.71

It is clear from the above result of experiments that S60 has maximum Dry Density. The

same result was reported by Sarvan et.al. (2005) and Soosan et. Al. (2002). It is also observed that % increase in CBR values increment is maximum in case of S60. From mix S60 to S80 although the absolute value of CBR is increasing but % increases in the increase of CBR value is decreases i.e. from 26.91 to 26.91%. Therefore S60 mix is choose as the optimum mix for further research. Coir fibers strips cut into small pieces and had been mixed randomly to this soil-waste mix to assess the improvement in the strength and stability characteristics. The reinforcement were added by percentage of weight of the soil-waste matrix same. The coir percentage was taken as 0.75, 1.5, 2.25 and 3.0%. The aspect ratios selected for study were taken as 50, 75 and 100.

• The test Result is tabulated below for S60 mix

Aspect ratio Coir fiber % MDD kN/m3

OMC %

0 20.2 11.8 50 0.75 19.8 13.0 50 1.5 19.6 13.9 50 2.25 19.4 14.8 50 3.0 19.3 15.6 75 0.75 19.7 13.2 75 1.5 19.6 13.9 75 2.25 19.5 14.9 75 3.0 19.2 15.7 100 0.75 19.7 13.7 100 1.5 19.5 14.1 100 2.25 19.3 15.0 100 3.0 19.1 15.7

CBR test for S60 mix with different proportion of coir fiber into different aspect ratio were

conducted. The result of which are as below:

Aspect ratio Coir fiber % CBR soaked % increase 0 10.9 50 0.75 11.98 9.9 50 1.5 13.16 20.73 50 2.25 14.70 34.86

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50 3.0 14.78 35.5 75 0.75 14.5 33.0 75 1.5 15.6 43.11 75 2.25 16.9 55.0 75 3.0 16.6 52.29 100 0.75 14.57 33.66 100 1.5 17.2 57.7 100 2.25 18.8 72.47 100 3.0 18.0 65.13

The moisture condition of the sub grade, which the test sample is expected to simulate is

governed by local environment factors, such as water table, precipitation, soil permeability, drainage condition water proof ness of the pavement and flood frequency etc. Hence the design of new construction should be based on the strength of the sample prepared at the moisture content and dry density corresponding to standard Proctor compaction and soaked in water for a period of four days. CBR values are most consistent when mould is compacted by automatic compactor and tested by using electrically operated load frame. From the test result it was observed that quarry dust alone gives higher CBR value. Soil and its combination showed higher value even without surcharge, this may be due to lack of cohesion between grains. It is also observed that in most of cases 5mm penetration CBR value is higher than the 2.5mm penetration values. This indicates that even at higher deformations addition of quarry dust is very effective in improving the stiffness and resistance to penetration.

Result of tests shows Addition of quarry dust result in increase of CBR values under soaked and unsoaked condition for S20 and S40 were 9.5% and 24.5% if compared with S0 value. The corresponding increase was 12.85 and 24.5% under soaked condition. But for sample S60 and S80 the increase was 62.9% and 82.0%. Sample S60 showed an increase of 34% in CBR (soaked) compared to the sample S40, whereas sample S80 showed an increase of only 19.1% compared to S60.

Soil reinforcement by randomly distributed discrete fibers is similar to the stabilization of soil by admixtures. The main advantage of randomly distributed fibers is ease of mixing, the maintenance of strength isotropy and the absence of potential planes of weakness that can develop parallel to the oriented reinforcement. Randomly distributed fibers reinforcement can be advantageously employed as a ground improvement technique with respect to embankment, sub-grade and other such problems. By going though previous work done in this field, Coir fiber of different percentage and different aspect ratio was mixed with sample S60, which was the optimum mix giving maximum increase in improvement of CBR value. From test result it is clear that as the quantity of coir fiber increases, CBR value increases for all aspect ratio except for 3% coir fiber. There is marginal decrease in CBR value. Therefore it is concluded that the optimum percentage of coir fiber is 2.25%. . It has been observed that the rate of increase in CBR is higher when coir fibers with high aspect ratio are added. This may be because of higher tensile strength of coir fiber. Increase in CBR value is due to increase in shear characteristics of fiber reinforced soil. Maximum benefit is derived when 2.25% coir fiber with aspect ratio 100 is added to the sample S60. CBR increases by 72.47%. If the result is compared with S0 sample CBR increases by 73%.

ECONOMICS IN PAVEMENT

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If the thickness is calculated for a Flexible pavement under a traffic condition as number of commercial vehicles per day exceeding three tones is greater than 4500, It comes to be 450mm for local soil without stone dust and coir fiber and the same is 230mm for a sub-grade prepared by the soil mix i.e. Local soil with 60% of stone dust and 2.25% of coir fibers with aspect ratio 100. It can be concluded that a significant saving may be achieved in construction of a flexible pavement over a sub-grade prepared with 60% stone dust and 2.25% coir fiber with aspect ratio as 100 over the pavement simply constructed over a sun-grade of local soil as thickness of pavement is reduced nearly half.

CONCLUSIONS

• It may be concluded that quarry dust is an Industrial waste, disposal of which is an

economical and environmental problem have been utilized in a sub base for both flexible and rigid pavements.

• The maximum dry density is obtained for samples with around 60% quarry dust. • Addition of coir fiber increases OMC and decreases MDD but increases CBR value.

Maximum improvement in soaked CBR value is derived when 60% quarry dust and 2.25% coir (Aspect ratio=100) is mixed with the base material.

• A significant saving i.e. about 40% may be achieved in construction of flexible pavement over a sub base of local soil mix with 60% quarry dust and 2.25% (AR=100)

References

Boben K, George, A.K, and Grish M.S. (1999) “ Effect of coir felt on deformation of sand beds” Coir News, Vol.28, No.3 Coir Board, India PP 17-22

Charan (1995) “Probabilistic analysis of randomly distributed fiber reinforced soil” Phd thesis, University of Roorkee, Roorkee, India

Das, B.M. (2000)” Principle of Geotechnical Engineering” Thomson Learing INC., Thomson Asia Limited, Singapore

Ghosal and Som (1989) “ Use of geosynthetics in India. Experiment and Potentail”, Edited by Roa and Sexsena, CBIP, New Delhi, PP 321-324

Gray D.H. and Mahar, M.H. (19890 “ Admixture stabilization of sand with discrete randomly distributed fibers” Proceeding 12th ICSMFE, Brazil. PP 1363-1366

Gupta, A.K. Sachan A.K, Sahoo A.k, (2002)’ Stabilization of Black cotton Soil using crusher dust”Proc. IGC-2002.pp 308-310Mahar, M.H, (1988)”

Static and dynamic response of sand reinforcement with discrete randomly distributed fibers” Phd. Thesis, University of Michigan<Ann Arbor. USA

Tingle S.J, Santoni, R.L., and Webster, R.L. (2002) “ Full scale field test of discrete- Reinforced sand” J.Transportation engineering, ASCE Vol-128, PP 9-16

Soosan George T, Babu T Jose and Benny M Abraham (2002) “ Improvement of Ground and Highway Sub base using quarry dust waste” Advanced on Concrete and Construction Technology, Banglore, PP 51-58

Mandal and Mohan (1989) “ Performance studies on CBR values using Geosynthetics”. Proceeding, International workshop on Geotextile, Banglore, PP 257

Nagrale P.P., Chandra, S and Viladkar, M.N., et.at (2005) “ Behavour of flexible pavements resulting on fiber reinforced sub grade soil” IGC-2005, Ahamdabad, PP 17-19

Mandal J.N. and Mhaiskar, S.Y (19900 “an overview of the pavement design with Geosynthetics’ Indian Road Congress, vol. 51-3, PP 805-836

Rakesh (1995) “Characteristics of Fiber Reinforced sand as pavement Sub grade’ M.E, Thesis , University Of Roorkee, Roorkee, India

556

BIOMEDICAL WASTE MANAGEMENT: INDIAN SCENARIO

Amanpreet Singh Virk, Manjeet Bansal and Gurpreet Singh Bath Department of Civil Engineering Punjab Technical University Giani Zail Singh Campus, Bathinda –151001

Abstract: In this paper the biomedical waste management and related issues in India are discussed. Biomedical waste is infectious and hazardous in nature can be a serious threat to the public health and the environment. The large variety of drugs used at hospitals and medical research organizations and the increasing number of such health care units results into massive growth of the biomedical waste. The society becoming aware about the adverse effects of biomedical waste therefore pushing the regulatory bodies to reducing the biomedical waste generation and implementing the proper biomedical waste management practices.

INTRODUCTION

India being one of the fastest growing countries in the world with a population of over 1.21 billion second largest on earth after China does not have as adequate and efficient system to deal with the problem of increasing solid waste. As per the census of India 2011 India’s share in total world population is 17.5%. As per the provisional census 2011 of India, 377 million people lives in urban areas of India accounting 31.16% of the total population of India. NCT Delhi has the largest proportion of urban population (97.5%). The census 2011of India shows that the urban agglomerations in India have increased from 384 UAs (from census 2001) to 475 UAs. Out of which three has a population of above 10 million. With the increase in population the needs of people also increases and today there is a gap between the increasing needs of people with increasing urbanization and available resources and services to meet these needs. Biomedical waste management is one of them that should be taken care on priority basis.

Waste can be categorized into solid, liquid and gaseous depending upon its physical state. Solid waste can be anything that comes out as a waste material from houses, hotels, restaurants, shops, schools, hospitals, office buildings, industries, construction and demolition sites, farms (dairy animals and pets), fallen tree leaves and branches etc. Depending upon the type and source of solid waste it can be divided into following categories. Household waste also known as municipal waste that includes waste from kitchens, sanitary, soil, debris, construction and demolition waste, and industries other than using chemicals.

Hazardous waste includes waste which is toxic, inflammable in nature. The main source of this type of waste is chemical waste from the industries therefore it is also known as industrial waste. Infectious waste may spread certain diseases and infections to humans and animals. The main source of infectious waste is the waste coming out from hospitals, clinical laboratories and medical colleges. Radioactive waste includes waste material of radioactive in nature which is very rarely found. The main focus of this report will be on the present biomedical waste management practices in India and available options.

BIOMEDICAL WASTE

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Biomedical waste is mainly the waste generated from the hospitals, medical institutions, clinical laboratories etc. it may be infectious, hazardous and radioactive in nature. Any waste that can spread infections can be treated as infectious waste for example human body parts, blood, used cotton, syringes, needles, dressings etc. The non-infectious waste from these medical facilities should be collected separately and can be disposed as general municipal solid waste but the infectious waste needs special care. The improper management of biomedical waste can cause serious infections and has direct impact on human beings and on the general environment.

• Current Scenario

Nowadays many health care units dump their biomedical waste which is infectious and hazardous in nature with their general municipal waste. Proper segregation practices and color coding system is not followed. Untreated sharps, syringes, needles etc. also dumped with other general waste in the garbage bins. The standards for proper biomedical waste management prescribed in govt. rules are not followed. All these practices of improper biomedical waste management are considered as a serious threat to the human health and general environment. Biomedical Waste Generation As shown in the table below the waste generation in India is 1-2 kg/bed/day one of the largest in Asia. Also the total waste generation in India is 330,000 tons/year, second largest after china in Asia.

Table 1: Medical waste generation estimate (Source: Medical waste management issues in Asia, C Visvanathan)

Country Waste generation (kg/bed/day)

Total waste generation (tons/year)

Bangladesh 0.8 -1.67 93,075 (only in Dhaka)

Bhutan 0.27 73

China - 730,000

India 1-2 330,000

Malaysia 1.9 --

Nepal 0.5 365

Pakistan 1.06 250,000

Sri Lanka 0.36 6,600 (only in Colombo)

Thailand 0.68 -- Metro Manila

(Philippines) -- 17,155

Vietnam 2.27(Hanoi) 60,000

BIOMEDICAL WASTE CATEGORIES

The schedule I of the draft 2011 of Ministry of Environment and Forests Bio-Medical Waste (Management and Handling) Rules 1998 divided the biomedical waste into eight categories and also recommended the treatment and disposal methods.

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• Public Health

Improper biomedical waste management can cause health infections such as respiratory infections, skin infections, HIV, hepatitis B&C etc. apart from the above said diseases it can also be the cause of other environmental problems decomposition of biomedical waste may generate foul odor within and surrounding the health care units creating an unhygienic environment for the patients and the staff. The dumping of waste provides favorable conditions for mosquito breeding and also attracts the stray animals that can spread infectious diseases. The municipal workers and the waste pickers at the dumping sites are more vulnerable to infectious diseases. Leachate formation at dumping sites contaminates the ground water and the open burning can produce dioxins and furans contributing significantly in polluting the air.

• Biomedical Waste Awareness

As per an online article biomedical waste management practices of doctors: an online snapshot, from the national journal of community medicine volume 3 issue April - June 2012 a study was conducted to assess the behavior of medical professionals regarding biomedical waste management in India. In this study a total of 557 e-mail contacts of medical professionals were obtained randomly from the internet and a predesigned questionnaire was sent and 364 e-mail replies were received in return. In this study the respondents has to self-assess their knowledge regarding biomedical waste and the results are shown in the table below.

Table 3: Respondents self-assessment of knowledge regarding BMW management Source: Biomedical waste management practices of doctors: an online snapshot

Knowledge self-assessment Number (%) Very poor (<30%) 181 (49.7) Poor (30-49%) 30 (8.2) Average (50-69%) 93 (25.5) Good (> 70%) 60 (16.5) Total 364 (100)

The self-assessed knowledge was categorized into four different categories as ‘good’ (remembered >70%), ‘average’ (50-69%), ‘poor’ (30-49%), ‘very poor’ (<30%). The table shows that about half of the respondents (49.7%) realized that they have forgotten more than 70% of what they have learned about biomedical waste management whereas 42% doctors claimed that they remembered at least 50% of what they knew. The study also reveals that only 57.7% of respondents were aware of all the four color of bags which are used for BMW segregation and 35.7% (one out of every three) respondents did not knew the symbol of bio-hazardous waste.

PROPER BIOMEDICAL WASTE MANAGEMENT

The above discussion clearly reflects the need of proper biomedical waste management techniques. There are several techniques of proper biomedical waste management running successfully all around the world. The available techniques are shown in a figure below.

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Figure 1: Biomedical waste treatment options

• Incineration

It is a high temperature oxidation process in which the waste is converted into inert material and gases under controlled combustion process. Multiple hearth, rotary kiln and controlled air type are the three types of the incinerators used for hospital waste. Oil or electricity or a combination of both can be used as a fuel for the incinerators. Incineration may pollute the environment through emission of dioxins, furans, nitrogen oxides, sulpher dioxide etc. therefore the use of incinerators is becoming unpopular all around the world. It is recommended for human anatomical waste, and work, discarded medicines etc.

• Autoclave

In this process the waste is disinfected by steam sterilization. The BMV is brought into direct contact with steam in a pressure vessel for sufficient time and at suitable temperature to disinfect the BMV. Autoclave is suitable only for sharps, soiled and solid waste etc. and not recommended for human anatomical, animal or pharmaceutical waste.

• Hydroclave

It is similar to autoclave but the steam sterilization is carried out in equipment called Hydroclave. The technology is free from harmful air emissions, chemical requirements, liquid discharges etc. The first hydroclave in India was installed by Tata Memorial, Mumbai in September 1999.

• Microwave Treatment

It is a thermal disinfection based technology in which the infections are destroyed by conduction. The spreading of waste to proper size and humidification is its basic requirement. It is not recommended for human anatomical, animal, or pharmaceutical waste. Though it is a small electrically operated with no steam requirements but it needs qualified technicians for its operations.

• Chemical disinfection

In this chemical treatment the shredded waste is brought in contact with 1% hypochlorite solution or any other equivalent chemical re agent for at least 30 minutes to disinfect one BMV

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and after proper disinfection the waste is land filled. Chemical disinfection is recommended for sharps, solid and chemical waste.

• Secure landfilling

These are predesigned landfills which are designed for the disposal of infections and hazardous BMV. As per the rules requirement the human anatomical waste, Animal waste when other proper treatment facility is not available, Autoclave, hydroclave, microwaved waste, incineration ash and sharps should be securely landfilled. The table below shows a comparison between different treatment technologies.

Table 4: Treatment technologies comparison (Source: Medical waste management issues in Asia, C Visvanathan)

Treatment Technologies

Incineration Autoclave Microwave Chemical Decomposition

Implementation & Operating Cost high moderate high Low

Suitability of the Waste not for radioactive all except pathological

all except cytotoxic, radioactive

Liquid waste

Ease of Operation no Yes yes Yes

Waste Volume Reduction Significant Low significant

Odour Problems yes Slight slight Slight

Environmental Friendly no Yes yes No

It is clear from the above table that the implementation and operational cost of incineration and microwave treatment technologies is high but low for chemical decomposition process. Autoclave and microwave technologies are environmental friendly with slight odor problems.

• Legislation

1. The Bio-medical waste (Management and Handling) Rules, 1998 notified by the Ministry of Environment and Forests (MoEF).

2. The colour coding and type of container as per Schedule II of the Bio-medical waste (Management and Handling) Rules, 1998.

3. Label for biomedical waste containers/bags. 4. The Bio-medical waste (Management and Handling) Rules, 1998 amended twice in the

year 2000 and the earliest in 2011. 5. Operating and emission standards for biomedical waste treatment and disposal units.

CONCLUSION

This paper is an effort to present the current and future challenges of biomedical waste management in India. The environmental and public health issues caused by improper BMW

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management are also discussed in this report. The unawareness of general public and medical personals about the BMW management and the adverse effects of improper waste management is a very serious issue. The government of India has also recognized this problem and notified biomedical waste management and handling rules 1998 but the current issues is to implement the prescribed rules, standards and installation of eco-friendly treatment units.

References

Final report on waste inventory (MSW & BMW) in West Bengal Gupta Anil Kumar Bio-Medical Waste (Management and Handling) Rules, 1998: Issues, Challenges

and Possible Solutions Harhay Michael O., Halpern Scott D., Harhay Jason S. and Olliaro Piero L. Health care waste

management: a neglected and growing public health problem worldwide Infection management and environmental plan guidelines for healthcare workers for waste

management and infection control in community health centres. Lt Col SKM Rao, Wg Cdr RK Ranyal, Lt Col SS Bhatia, Lt Col VR Sharma. Biomedical Waste

Management : An Infrastructural Survey of Hospitals, Mohapatra Archisma, Gupta Manoj K, Shivalli Siddharudha, Mishra CP, Mohapatra SC. Biomedical

waste management practices of doctors: an online snapshot Muduli Kamalakanta, Barve Akhilesh Challenges to Waste Management Practices in Indian Health

Care Sector Pollution control acts rules and notifications there under, CPCB Sikka Saurabh, Biomedical waste in Indian context. Sreekumar P R and Nair A S K, Biomedical waste disposal and its status in Kerala. Tewary Kamlesh, Kumar Vijay, Tiwary Pamit Biomedical Waste Management A Step Towards A

Healthy Future The gazette if India extraordinary part-i section- iii subsection-ii. Visvanathan C. Medical Waste Management Issues in Asia

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MECHANICAL PROPERTIES OF HIGH VOLUME FLY ASH CONCRETE AT

ELEVATED TEMPERATURES

Inderpreet Kaur, Umer Farooq and Harshdeep Singh Department of Civil Engineering, GNDEC, Ludhiana, India

Abstract: Fly ash can be used either as an admixture or as a partial replacement of cement or as a partial replacement of fine aggregates or total replacement of fine aggregate and as supplementary addition to achieve different properties of concrete. In the present study, the compressive strength, split tensile strength and modulus of elasticity of fly ash concrete at elevated temperature up to 120˚C with mix proportions of 1:1.45:2.2:1.103 with a water cement ratio of 0.5 by weight was determined. Cement was replaced with three percentages of fly ash. The percentages of replacements were 30, 40 and 50 % by weight of cement. Tests were performed for compressive strength, split tensile strength and modulus of elasticity.

INTRODUCTION Fly ash is a finely divided residue resulting from the combustion of pulverized coal and transported by the flue gases of boilers fired by pulverized coal. It is available in large quantities in the country, as a waste product, from a number of thermal power stations and industrial plants using pulverized coal as fuel from boilers. Its availability is likely to increase with the increased industrialization in the country. Fly ash resulting from the combustion of pulverized coal in boiler of thermal plant is grey in color and alkaline in nature. The particle size may correspond to that of silty sand to silty clay i.e. between 5-120 microns. At thermal plants at Ropar, Bathinda and Lehra Mohabat, the fly ash collected in the ash hopper is removed from boilers house by wet as well as dry system. In the dry system the ash collected in silos where from it is available for various uses. In the wet system, fly ash is mixed with water in a mixing sump to form ash slurry and is pumped into ash ponds. Table 1.1 present chemical and physical requirements for fly ash and natural pozzolans for use as a mineral admixture in Portland cement concrete and Table 1.2 present chemical requirement of fly ash.

• Classification of Fly Ash

ASTM – C 618-93 categorizes natural pozzolans and fly ashes into the following three categories: -

1. Class N Fly ash: Raw or calcined natural pozzolans such as some diatomaceous earths, opaline chert and shale, stuffs, volcanic ashes and pumice come in this category. Calcined kaolin clay and laterite shale also fall in this category of pozzolans.

2. Class F Fly ash: Fly ash normally produced from burning anthracite or bituminous coal falls in this category. This class of fly ash exhibits pozzolanic property but rarely if any, self-hardening property.

3. Class C Fly ash: Fly ash normally produced from lignite or sub- bituminous coal is the only material included in this category. This class of fly ash has both pozzolanic and

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varying degree of self cementitious properties. (Most class C fly ashes contain more than 15 % CaO. But some class C fly ashes may contain as little as 10 % CaO.

Table 1: Requirements for fly ash and natural pozzolans for use as a mineral admixture in Portland cement

concrete as per ASTM C 618-93.

Requirements Fly Ash Classification N F C

Chemical Requirements

SiO2 + Al2O3 + Fe2O3, min % 70.0 70.0 50.0 SO3, max % 4.0 5.0 5.0 Moisture content, max % 3.0 3.0 3.0 Loss on ignition, max % 10.0 6.0 6.0 Physical Requirements Amount retained when wet sieved on 45 Om. Sieve, max %

34 34 34

Pozzolanic activity index, with Portland cement at 28 days, min % of control

75 75 75

Pozzolanic activity index, with lime, at 7 days, min (MPa)

5.5 5.5 -

Water requirement, max % of control 115 105 105

Autoclave expansion or contraction, max% 0.8 0.8 0.8

Specific gravity, max variation from average. 5 5 5

Percentage retained on 45 sieve, max Variation, and percentage points from average

5 5 5

Table 2: Chemical Requirements

S.No. Characteristics Requirement

(%) 1. Silicon dioxide (SiO2) + aluminium oxide (Al2O3) +

iron oxide (Fe2O3), percent by mass, Min 70.00

2. Silicon dioxide (SiO2), percent by mass, Min.

35.00

3. Magnesium oxide (MgO), percent by mass, Max.

5.00

4. Total sulphur as sulphur trioxide (SO3), percent by mass, Max.

2.75

5. Available alkalis as sodium oxide (Na2O), percent by mass, Max.

1.5

6. Loss on Ignition, percent by mass, Max.

12.0

7. Moisture content, percent by mass

3.0

• High-Volume Fly Ash Concrete

Fly ash, a principal by-product of the coal-fired power plants, is well accepted as a pozzolanic

material that may be used either as a component of blended Portland cements or as a mineral

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admixture in concrete. In commercial practice, the dosage of fly ash is limited to 15%-20% by mass of the total cementitious material. Usually, this amount has a beneficial effect on the workability and cost economy of concrete but it may not be enough to sufficiently improve the durability to sulfate attack, alkali-silica expansion, and thermal cracking. For this purpose, larger amounts of fly ash, on the order of 25%-35% are being used. From theoretical considerations and practical experience the authors have determined that, with 50% or more cement replacement by fly ash, it is possible to produce sustainable, high-performance concrete mixtures that show high workability, high ultimate strength, and high durability. With HVFA concrete mixtures, depending on the quality of fly ash and the amount of cement replaced, up to 20% reduction in water requirements can be achieved. This means that good fly ash can act as a superplasticizing admixture when used in high-volume. The phenomenon is attributable to three mechanisms. with a HVFA concrete mixture containing 50% cement replacement with a Class F fly ash, the adiabatic temperature rise is expected to be 30- 35ºC.

EXPERIMENTAL PROGRAMME • Material

The main objective of testing was to know the behavior of concrete with replacement of

cement with high volume fly ash at elevated temperature up to 120˚C. The main parameters studied were compressive strength, split tensile strength, modulus of elasticity. The materials used for casting concrete samples along with tested results are described.

• Fly Ash

Investigations were made on fly ash procured from Guru Gobind Singh Super Thermal Power Plant, Ropar, and Punjab. It was tested for chemical and physical properties per ASTM C 311.The chemical and physical properties of the fly ash used in this investigation are listed in Table 2.1 and Table 2.2 respectively.

Table 2.1 Chemical Composition of Fly Ash

S. No. Particulars Requirement ASTM C 618(%)

Test Results (%)

1. (SiO2+Al2O3+Fe2O3), % 70.0 min 91.69 2. SiO2, % 35.0 min 59.08 3. MgO 5.0 max 0.36 4. Sulphuric Anhydride, % 3.0 max 0.11 5. Total Alkali as Na2O, % 1.5 max 0.62 6. Total Loss on Ignition, % 5.00 max 2.08

Table 2.2 Physical Properties of Fly Ash

S.

No. Particulars Requirement

ASTM C 618 Test Results

1. Fineness Specific Surface (cm2/gm)

3200 min 3258

2. Residue on 45 micron (wet sieving)

34 max 30.17

565

3. Lime Reactivity (kg/cm2) 45 min 51.03

4. Compressive strength (kg/cm2), 28 days

Not less than 80% of strength of corresponding plain cement Mortar cubes

85.99

5. Dry shrinkage, % 0.15 max 0.04

6. Soundness expansion by auto clave, %

0.8 max 0.03

• Mix design

Concrete mix has been designed based on Indian Standard recommended Guidelines .The

proportions for the concrete, as determined were 1:1.45:2.2:1.103 with water cement ratio of 0.5 by weight. One control mixture M-0 was designed per Indian Standard Specifications IS: 10262-1982 [29] to have 28-day compressive strength of 23.05 MPa. The other concrete mixtures were made by replacing cement with 30%, 40%, and 50% of Class F fly ash by mass. In doing so, water-to-cementitious materials ratio was kept almost same to investigate the effects of replacing cement with high volumes of Class F fly ash when other parameters were almost kept same.

• Fresh concrete properties

Fresh concrete properties, such as slump, unit weight, temperature, and air content, were determined per Indian Standard Specifications IS: 1199-1959.

RESULTS Temperature is one of the main factors that influence the strength. High temperature induces a loss of strength (both in compression and tension) and stiffness (Young’s modulus). At high temperatures, chemical transformation of the gel weakened the matrix bonding, which brought about a loss of strength of fly ash concrete.

• Compressive Strength

Fig. 3.1 to 3.4 shows the variation of compressive strength with replacements with Class F fly ash at various temperatures (40ºC, 80ºC, 100ºC, and 120ºC). The compressive strength was calculated as the average of three cylinder tests. Compressive strength also decreased with the increase in temperature. At 120ºC temperature, the compressive strength decreased by 11.4%, 30.1%, 28.9%, and 27.5% when compared to normal temperature for 0%, 30%, 40%, and 50% replacement of fly ash with cement respectively at 56 days. At high temperatures, chemical transformation of gel weakened the matrix bonding, which brought about a loss of strength of fly as concrete.

• Split tensile strength

It was found that split tensile strength of Class F fly ash concrete (using 30 %, 40 % and 50 %

fly ash and a w/c of 0.5) at different temperature depended on the percentage of fly ash used and

566

temperature. The variation of split tensile strength was shown in table 4.2.the variation in splitting tensile strength with fly ash content and temperature was similar to that observed in case of compressive strength. Fig. 4.13 to 4.16 shows the variation of split tensile strength with replacements with Class F fly ash at various temperatures (40ºC, 80ºC, 100ºC, and 120ºC).

• Modulus of elasticity

In this investigation, the modulus of elasticity, which is also called secant modulus, is taken as the slope of the chord from the origin to some arbitrary point on the stress-strain curve. The secant modulus calculated in this study is for 33% of the maximum stress. Modulus of elasticity of concrete mixtures was determined at the ages of 28 and 56 days. Results are given in the Table 4.3 and shown in Figs 4.25 to 4.36.

Fig. 3.1 Compressive Strength vs Replacement of Fly ash (56 days)

Fig. 3.2 Compressive Strength vs Replacement of Fly ash (28 days)

567

Fig. 3.3 Compressive Strength vs Temperature (56 days)

Fig. 3.4 Compressive Strength vs Temperature (28 days)

0

5

10

15

20

25

0 20 40 60 80 100 120 140

Com

pres

sive

Stre

ngth

,MPa

Temperature, degree

Mix 1(0% FA)

Mix 2(30% FA)Mix 3(40% FA)Mix 4(50% FA)

568

Fig. 3.5 Split Tensile Strength vs Replacement of Fly ash (56 days)

Fig. 3.6 Split Tensile Strength vs Replacement of Fly ash (28 days)

0

0.5

1

1.5

2

2.5

3

3.5

0 10 20 30 40 50 60Split

ting

Tens

ile S

treng

th, M

Pa

Replacement of Fly ash, %

room temperature

80 degree celcieus

100 degree celcieus

120 degree celcieus

0

0.5

1

1.5

2

2.5

3

0 20 40 60

Split

ting

Tens

ile S

treng

th, M

Pa

Replacement of Fly ash, %

room temperature80 degree celcieus100 degree celcieus120 degree celcieus

569

Fig. 3.7 Split Tensile Strength vs Temperature (56 days)

Fig. 3.8 Split Tensile Strength vs Temperature (28 days)

0

0.5

1

1.5

2

2.5

3

3.5

0 20 40 60 80 100 120 140

Split

ting

Tens

ile S

treng

th, M

Pa

Temperature, degree

Mix 1(0% FA)

Mix 2(30% FA)

Mix 3(40% FA)

Mix 4(50% FA)

0

0.5

1

1.5

2

2.5

3

0 20 40 60 80 100 120 140

Split

ting

Tens

ile S

treng

th, M

Pa

Replacement of Fly ash, %

Mix 1(0% FA)

Mix 2(30% FA)

Mix 3(40% FA)

Mix 4(50% FA)

570

Fig. 3.9 Modulus of Elasticity vs Replacement of Fly ash (56 days)

Fig. 3.10 Modulus of Elasticity vs Replacement of Fly ash (28 days)

0

5

10

15

20

25

30

0 10 20 30 40 50 60

Mod

ulus

of E

last

icity

, GPa

Replacement of Fly ash, %

room temperature

80 degree celcieus

100 degree celcieus

120 degree celcieus

02468

101214161820

0 10 20 30 40 50 60

Mod

ulus

of E

last

icity

, GPa

Replacement of Fly ash, %

room temperature80 degree celcieus100 degree celcieus120 degree celcieus

571

Fig. 3.11 Modulus of Elasticity vs Temperature (56 days)

Fig. 3.12 Modulus of Elasticity vs Temperature (28 days)

CONCLUSIONS

The following conclusions are drawn from this study:

• Compressive strength of concrete decreased with the increase in cement replacement with Class-F fly ash. However, at each replacement level of cement with fly ash, an increase in strength was observed with the increase in age.

• With the variation of temperature compressive strength changed. With the rise in temperature from room temperature to 120˚C, compressive strength decreased.

0

5

10

15

20

25

30

0 50 100 150

Mod

ulus

of E

last

icity

, GPa

Temperature, degree

Mix 1(0% FA)

Mix 2(30% FA)Mix 3(40% FA)Mix 4(50% FA)

02468

101214161820

0 20 40 60 80 100 120 140

Mod

ulus

of E

last

icity

, GPa

Temperature, degree

Mix 1(0% FA)

Mix 2(30% FA)

Mix 3(40% FA)

Mix 4(50% FA)

572

• Splitting tensile strength and modulus of elasticity increased with increase in age at each replacement level of cement with fly ash up to 50% but they were decreased with increase in volume of fly ash.

• Increase in temperature up to 120˚C decreased the splitting tensile strength and modulus of elasticity, this is due to the chemical transformation of the gel weakened the matrix bonding, which brought about a loss of strength of fly ash concrete at high temperatures.

• The specimens failed after the formation of a number of longitudinal (vertical) cracks in the loading direction, and no shear type failures occurred.

References Cheng, F.P., Kodur, V.K.R., and Wang T.C., Stress- Strain Curves for High Strength Concrete a

Elevated Temperatures, Journal of Materials in Civil Engineering, ASCE, Jan-Feb 2004, pp. 84-90. Estakhri, C., and Mohidekar, S.D., Potential for reduced greenhouse gas Emissions in texas through

the use of High volume fly ash concrete, Research Report 167709-1, March 2004. Felicetti, R., and Gambarova, P.G., Effects of High Temperature on the Residual Compressive Strength

of High-Strength Siliceous Concretes, ACI Materials Journal, Vol. 95, No. 4, July- Aug. 1998, pp. 395-406.

IS: 8112-1989, Specifications for 43-Grade Portland cement, Bureau of Indian Standards, New Delhi, India.

IS: 383-1970, Specifications for Coarse and Fine Aggregates from Natural Sources for Concrete, Bureau of Indian Standards (BIS), New Delhi, India.

IS: IS: 9103:1999,ASTM C-494 Type F, BS 5057 part III, New Delhi, India. IS: 10262-1982, Recommended Guidelines for Concrete Mix Design, Bureau of Indian Standards

(BIS), New Delhi, India. IS: 516-1959, Indian Standard Code of Practice- Methods of Test for Strength of concrete, Bureau of

Indian Standards (BIS), New Delhi, India. IS: 1199-1956, Indian Standard Method of Sampling & Analysis of Concrete, Bureau of Indian

Standards (BIS), New Delhi, India.

573

CLIMATE RESPONSIVE BUILDING DESIGN

USING EFFICIENT BUILDING FORM,

ORIENTATION AND PASSIVE TECHNIQUES

Jatinder Kaur, Ripu Daman Singh Department of Architecture, PTU GZS Campus, Bathinda

Abstract: The ever alarming cost of energy in buildings enforces a statuary demand of energy

conservation passive design techniques in buildings. Modern buildings reveal inadequate thermal

performance and require mechanical devices to bring thermal comfort. Industrialization and

technological development exerts excess load on the local environment in terms of increasing energy

demand. It is, therefore, essential to investigate the better design options in terms of whole building

system. The present study briefs the analysis and design approach for Energy efficient design

strategies through efficient building form, orientation and passive techniques in composite climate.

The paper focuses on design strategies for making building highly energy efficient and sustainable in

terms of orientation, fenestration and shading devices.

INTRODUCTION

Building form can affect solar access and wind exposure as well as the rate of heat loss or heat gain

through the external envelope.

The general design objectives are given as:-

Contain the building’s exposure to external elements through compact building envelopes and careful

consideration of the treatment of different elevations,

Use sheltering and buffering to articulate the building mass so that building is shaded most of the

times.

Fig. 1 Energy use in India (TERI:

Sustainable Building Design Manual

Volume)

574

COMPACTNESS AND ZONING

A built form and the environment share the most complementary relationship in a sustainable design

process. The basic idea of compactness and zoning is to modulate the built form in terms of its built

mass proportions, density and size, surface to volume ratios and the zoning of the built form on site as

per the wind direction and solar orientation. A compact building gains less heat during the day and

loses less heat at night. The compactness of the building is

measured using a ratio of surface area to volume:-

Compactness = S/V where,

S = Surface area V = Volume

In hot dry climates, The S/V ratio should be as low as

possible to minimize heat gain. In cold-dry climates, S/V

ratios should also be as low as possible to minimize heat

losses. In warm-humid climates, the primary concern is to

create air\ spaces: this might not, however necessarily

minimize the S/V ratio. Further the materials of

construction should be such that they do not store heat.

Compact planning

If two building designs under consideration enclose the same volume, the one with the more

compact plan will have greater thermal efficiency. A square floor plan is more thermally efficient than

a rectangular one because the surface area over which it loses or gains heat is lesser.

Streets or walkways on site

The ratio of street width to building height determines the altitude up to which solar radiation can

he cut off. Similarly street orientation determines the azimuth up to which solar radiation can be cut

Fig. 2 Varying S/V ratio of Building types

Fig. 3 Different Plan Forms (TERI: Sustainable Building Design Manual Volume 1)

575

off. Their effective combination should or optimized in the compact planning of the built form on large

sites.

Low perimeter to area ratios

The P/A (perimeter to area) ratios indicate radiative gains or losses and efficient ventilation. Low

P/A ratios are suitable for hot-dry climates. Plan form, which enhances ventilation, is not an important

issue in hot-dry climates, as the breeze is often warm.

ORIENTATION

The amount of solar radiation falling on surfaces of different

orientation varies considerably depending on the view or exposure

to the sun. In composite climates, east and west receive the

maximum solar radiation during summer. Southward orientation has

radiation during the winters, which can be potentially used during

cold periods. Orientation also plays an important role with regard to

wind direction, especially in hot and humid climates. At the

building level, orientation is considered as per the surrounding built

form. Orientation may affect the daylight factor, increase the

reflected radiation component and thus overshadow and divert the

winds.

SHADING DEVICES

Fig. 4 Building Orientation w.r.t. Sun

External shading devices Internal shading devices

These may be of fixed or movable type. Fixed shading

devices include vertical louvres, horizontal louvres, and egg

crate type. The horizontal louvres are effective against the

high altitude sun in summer while the vertical louvres protect

the window from the north-west and south-west solar

radiation. The egg crate type is well suited for westward

orientation. The movable shading devices are more

advantageous, as they can be adjusted to allow winter sun and

to cut direct summer radiation.

These include vertical blinds,

curtains, and roller devices. The

performance of the internal devices

depends on the colour, reflective

index, fabric, and the air tightness.

Table 1 Shading Devices – External and Internal

576

PASSIVE TECHNIQUES

Heating strategies

Heat losses from buildings occur

mainly by conduction through sand in the

external surface by infiltration and

ventilation through cracks and openings in

the building envelope. Reducing this loss

by improved insulation and infiltration can

decrease the heating cost of the building.

DESIGN CRITERIA

•Reduce heat loss by insulation and infiltration

•Use passive solar elements for heat gain and storage

Direct gain

The direct gain consists primarily of a well-insulated building with a relatively large expanse of

south- facing glazing, which admits the low- angle rays of the winter sun. The building needs thermal

mass to store heat during the day and to re-emit it at night, reducing the temperature fluctuation during

the night. The basic requirement for a direct gain system is a large vertical south- facing window. The

use of double- glazing with a sealed joint is the effective solution.

Advantages

Direct gain is the simplest solar heating system and can be the easiest to build. The system is very

cost- effective and the only cost involved is that of insulation.

Disadvantages

Fig. 6 Combined Passive System

Fig. 5 Types of Horizontal Shading Devices in Composite Climate (TERI: Sustainable Building Design Manual

Volume 1)

577

A larger area of glass can result in glare. The system should be well designed in terms of heat storage

with respect to the glazing area. An improperly designed system can result in increase in the inside

temperature during the day

Indirect gain

The trombe wall, mass wall, water wall, and roof pond are all indirect gain systems that combine

collection, storage, and distribution functions within some part of the building envelope, which

encloses the space.

Mass and trombe wall

In the mass and trombe wall systems, the thermal storage mass for the building is a south-facing

wall of masonry or concrete construction with a glazed external surface to reduce heat losses to the

outside. The trombe wall is the ventilated mass wall with openings at the top and bottom of the wall to

allow air to circulate to the heated space.

Advantages

• Swings in temperature in the living space are lower than direct gain systems.

• The time delay between absorption of the solar energy and delivery of the thermal energy to the

living space can be used for night-time heating.

Disadvantages

• The system is expensive as compared to the direct system.

• The visual link with the outside can be cut or reduced.

• Condensation on the glass can be a problem.

Fig. 7 Non Diffused Heat Gain Fig. 8 Diffused Heat Gain

Fig. 9 Mass Wall and Trombe Wall

578

Water wall

A water wall is similar to the trombe wall except that water is used for storage instead of masonry.

Water has a greater capacity to store heat per unit volume than brick or concrete, and the convection

current within the water causes it to act as an almost isothermal heat store. The selection of the

material and form of container is an important factor in the operational efficiency of the system.

Advantages

The isothermal nature of heat storage results in a reduced temperature on the external surface, losing

less energy at night.

Temperature variations in the living space are lower than in a direct gain or convective loop system

PASSIVE COOLING STRATEGIES

In the cooling strategy, first control the amount of heat gained from solar radiation and hot air that

reaches the building then minimize the effect of unwanted solar heat within the building skin or

through openings. Next, reduce the internal heat gains from appliances or occupants, and finally use

environmental heat sinks to absorb any remaining unwanted heat by applying:-

Evaporative cooling,

Radiative cooling,

Ground cooling, and

Ventilation.

Evaporative Cooling

Principle Evaporation occurs whenever the vapour

pressure of water is higher than the partial pressure of

water vapour in the adjacent atmosphere. The change in

the phase of water from liquid to vapour is

accompanied by the absorption of a large quantity of sensible heat from the air that lowers the dry bulb

temperature of the air while the moisture content of the air is increased.

Fig. 10 Water Wall

579

Direct evaporative cooling systems

The direct evaporative cooling systems — such as fountains, pond, pools, and wind towers — are

very effective in hot and dry zones where with cooling, the increase in humidity gives additional

comfort. In the case of fountains, water sprinkles in the air with an increased surface area and thus

increasing the evaporation rate. This water sprinkled into the air also cleans dust particles from the air.

Indirect evaporative cooling system

In roof sprays and roof ponds, external cooling through humidification can be achieved by

keeping the surfaces of roofs moist by using sprays or lawn sprinklers. The surface temperature can be

reduced by up to 30 °C. However, water consumption is excessive in this case.

RADIATIVE COOLING

Any object emits energy in the form of electromagnetic radiation. If two elements at different

temperatures are kept facing one another, a net radiant heat loss from the hotter element n ill occur

until a state of equilibrium between the two elements is achieved.

Radiative cooling strategies

Nocturnal cooling

Nocturnal cooling or night sky cooling can be a very low-energy passive system, and can be

effectively used in office buildings, institutions, and residential buildings.

.

Roof pond with movable insulation

580

A roof pond system with a movable insulation is a perfect example of radiative cooling

GROUND COOLING

Throughout the year, the earth’s temperature is practically constant after a depth of 2.5 m, and remains

close to the average annual (yearly average) temperature thus offering a vital ‘sink’ for the dissipation

of a building’s excess heat. Heat dissipation into the ground can be achieved by conduction or by

convection.

VENTILATION

Ventilation is often considered to be the most energy-efficient and healthy solution. Thermal comfort

depends largely on ventilation, along with other factors such as air temperature and relative humidity.

A well-designed thermal structure can dampen the outside temperature fluctuations to a certain level,

but further efficiency can only be achieved by ventilation.

Fig. 13 Roof Pond System with Movable insulation

Fig. 14 An Earth Berm Structure

Fig. 12 Nocturnal cooling

581

Table 2 Natural and Mechanical ventilation

CONCLUDING REMARKS

Accelerated urbanization in the Indian context imposes immense pressure on the dwindling energy

resources. However, the resource crunch confronting the energy sector can be effectively alleviated if

we plan, design and develop human settlements and buildings by using appropriate strategies and

incorporating sound concepts of energy efficiency and sustainability. Adopting holistic and integrated

approach, shared accountability and responsibility towards improved energy performance, making

energy more valued by educating and motivating professionals involved in building industry would be

critical to promote energy efficient buildings.

References

Craig A.Langston and Grace K.C.Ding: Sustainable practices in the built environment.

Bansal N K, Hauser G, Minke G. Passive building design: A handbook of Natural climatic control

Manual on solar passive architecture: energy systems engineering IIT Delhi and Solar Energy Centre,

Ministry of Non-conventional Energy Sources, Government of India

Natural ventilation Mechanical ventilation

The movement of outdoor air into a space

without mechanical assistance; it can be

controlled by intentionally providing openings

such as windows, doors, and non-powered

ventilators. These openings provide a level of

ventilation in addition to infiltration.

The movement of air by mechanical means to and

from a space. It is controllable and can be localized

(by using individual wall or roof fans) or centralized

(with ducted distribution). Infiltration occurs also in

mechanically ventilated spaces. The best practice is

to minimize infiltration for controllable natural and

mechanical ventilation.

Fig. 16 Cross Ventilation and Stack Ventilation Systems suck the fresh air in and throw the stale air out of a room

582

Koenis Beger, Inger Soll, Mayhew and Szokolay: Manual of Tropical Housing and Building.

Tanushree Mohanty: Holistic approach to sustainable buildings - A Thesis report, deptt. of B.E.M., S.P.A.,

New Delhi.

Aprajita Bhattacharya: Energy consumption norms for offices and residences – A Thesis report, deptt. of

B.E.M., S.P.A., New Delhi, January 1999.

LEED reference guide, USGBC, version 2.1.

TERI: Sustainable Building Design Manual Volume 1 and 2.

TERI: Energy efficient Buildings in India.

Websites

www.leedbuilding.org – LEED

www.builtgreen.net – Built Green

www.egret.net – Breaking through the Barriers to Sustainable Building

www.greenbusinesscentre.com – ITC green building portal

AUTHOR INDEX

A Ashutosh Trivedi

(Key Note Speaker)

A.K. Singh, 263

A Kameshwar Rao, 296

A.Murali Krishna, 330

Amandeep Singh, 439

A.Kavitha, 451

Ankit Sharma, 459

Amanpreet Kaur, 465

A K Choudhary, 509

Amanpreet Singh Virk, 556

B Binu Sara Mathew, 422

B S Walia, 447

C C S Gokhle, 523

D Dhiraj Raj, 301

G Gurbir Jawanda, 391

Gayathri Mohan, 422

Gurdeepak Singh, 447

Gurdeep Singh, 481

Gurcharan Singh, 550

Gurpreet Singh Bath, 556

H Harpal Singh, 290

Harvinder Singh, 321,517

H K Gaba, 343

H S Rai, 343

Harpreet Kaur, 400

H K Khullar, 517

Harshdeep Singh, 562

I Inderpreet Kaur, 562

J J N Jha, 263,321,375,439,481,517

Jagbir Singh, 277

Jasbir Singh, 375

J. Parveen, 459

J K Naik, 532

Jatinder Kaur, 573

K K. G. Guptha, 356

K.S.Gupta, 161

Kiranmaye Dasai, 170

KS Bedi, 385

Kanwarjeet Jeet Singh Bedi, 400

Karanbir Singh, 488

K S Gill, 439,481,488,509,517

M M. Bharathi, 301

M. Anwakar, 335

Manas Ranjan Das, 412

M.Ganeshram, 451

M. Mohanty, 501

M. Panda, 501

Manpreet Singh, 538

Manjeet Bansal, 556

P Pinal Saini, 277

Priyanka Jain, 296

Prashant Garg, 321

P. Sayoikar, 335

Parveen Chander, 375

Pardeep Singh, 495

P Y Sarang, 523

P P Savoikar, 523

Prashant Garg, 550

R Rajesh Kumar, 277

Rajiv Chauhan, 283,349

Rahul Patidar, 296

Rajesh Kumar, 375

Rakhjinder Singh, 385

AUTHOR INDEX

R K Dutta, 430

Rajiv Kumar, 447

Ranjit Prasad, 509

Ramandeep Kaur, 538

Ripu Daman Singh, 573 S S. Unnikrishna Pillai, 255

S. K. Shukla, 263

Sanjeev Aggarwal, 268

S M Jalali, Sneha Rao, 296

S. Bali Reddy, 330

S. Shaikh, 335

S P Singh, 343,532

Surender Singh, 349

S.A. Kakodkar, 356

Sasmita Sahoo, 367

Siddharth Das, 421

Sarat Kumar Das, 412

S.Boobathi Raja, 451

Sachin Dass, 459

S Tripathy, 532

Sarpreet Singh, 538

Sanjeev Naval et al, 544

U U. Chattaraj, 501

Umer Farooq, 562

V Vaishali Sahu, 1

V. Gayathri, 2

Vikramjit Singh, 43

V. M. Karpe, 68

V.A. Sawant, 101

Vijay Devar, 123