stabilization of black cotton soil

A

PROJECT REPORT

ON

STABILIZATION OF BLACK COTTON SOIL

(SUBGRADE SOIL) USING LIME AND FLY ASH

SUBMITTED BY

SOMDATT DAHIYA

09EELCE055

IN PARTIAL FULFILLMENT OF

THE REQUIREMENT FOR THE DEGREE OF

BACHELOR OF TECHNOLOGY

IN

CIVIL ENGINEERING

OF

GOVT. ENGINEERING COLLEGE, BHARATPUR, RAJASTHAN

UNDER THE GUIDANCE

OF

Dr. BISWJIT ACHARYA

DEPARTMENT OF CIVIL ENGINEERING

GOVT. ENGINEERING COLLEGE, BHARATPUR, RAJASTHAN

2012-2013

Stabilization of black cotton soil using lime and fly ash 2

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CERTIFICATE

This is to certify that, the project entitled

STABILIZATION OF BLACK COTTON SOIL

(SUBGRADE SOIL) USING LIME AND FLY ASH

Submitted by

Mr. SOMDATT DAHIYA

Is a record of his own work carried out by him in partial fulfillment

for the award of

BACHELOR OF TECHNOLOGY

IN

CIVIL ENGINEERING

Govt. engineering college, Bharatpur,

rajasthan

Under my guidance during the academic year

2012-2013

Date :

Place:BHARATPUR

Dr. Biswajit Acharya Er. Amit Daiya

(ProjectGuide) (H.O.D)

DEPARTMENT OF CIVIL ENGINEERING

GOVT. ENGINEERING COLLEGE, BHARATPUR

2012-2013


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Acknowledgement

When we take a glance over our journey throughout the year, few respectful and

friendly faces and encouragement come across our mind. What we remember the most is

the immense help, guidance and teachings of our project guide Dr. Biswajit Acharya

without whom working in this project would have been walking on an unknown path. He

who has taken sincere efforts to lead us, he who taught us how to plan, work and analyze

and he who made us discover our hidden qualities will be always remembered by us for

the teachings and principles he taught us during the project course. We would like to

thank him for being such an excellent teacher, a perfect guide, a strict disciplinarian, an

indefatigable leader and a true friend.

We are grateful to Er. Priyanka Gupta for their timely and valuable guidance. We

are grateful for the guidance and kind support of our H.O.D, Er. Amit Daiya. We would

like to extend our gratitude towards the supporting staff for being very helpful. We are

very grateful to those who in the form of books had conveyed guidance in this project

work.

At last, we would like to thank our friends and family for their support and

encouragement throughout the year.

Mr. SOMDATT DAHIYA

B.Tech. civil


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Abstract

From the recent past years people are facing the problems on construction of road on

black cotton soil. In construction of roads on BC soils, the behavior of soils with respect

to water poses a big problem.

The soil undergoes high swelling shrinkage and has poor subgrade strength.

Stabilization of sub grade soil helps to achieve required strength of subgrade, eliminate

the associated problems and this reduces the thickness of pavement.

Our project aims to stabilize black cotton soil using fly ash and lime mixture; thus the

project work includes finding optimum proportion of soil, fly ash, lime mixture which is

acceptable, applicable and economical.


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INDEX

CHAPTER

NO.

CHAPTER NAME

CONTENTS PAGE

NO.

1.

INTRODUCTION

1.1 Introduction of the project 9

2.

LITERATURE

REVIEW

2.1 black cotton soil

2.2 problems associated with black cotton

soil

2.3 stabilization of soil

2.4 lime stabilization

2.5 fly ash stabilization

2.6 lime + different materials for

stabilization

2.7 lime + fly ash stabilization

2.8 Materials and their types

11

3. OBJECTIVES OF

THE PROJECT 3.1 objectives of the project 28

4.

METHODOLOGY

4.1 properties of local soil

4.2 preparation of samples for tests

4.3 curing of samples

4.4 testing of samples

30


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5.

RESULTS AND

DISCUSSIONS

5.1 Preliminary observations and readings

5.1.1 Properties of black cotton soil

5.1.2 Unconfined compressive strength

tests results of different proportions

5.1.3 Effect on strength when fly ash is

varied keeping lime constant

5.1.4 Effect on strength when lime is

varied keeping fly ash constant

5.1.5 Effect of curing time on the strength

of the sub grade

5.1.6 Discussions about the preliminary

reading

5.2 Final Observation and readings

5.2.1 Variation in compressive strength

with variation in fly ash (explained using

bar chart)


with variation in lime (explained using bar

chart)


with variation in fly ash (explained using

line graphs)


with variation in lime (explained using line

graphs)

5.2.5Discussions about the final readings

obtained:

5.2.6Properties of black cotton soil

with12% lime and 30% fly ash

5.5.7 Comparison between black cotton

soil with no stabilizer and black cotton soil

added with 12% lime and 30% fly ash

40


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6. APPLICATION

FORMULA

6.1 Explanation of the derivation of

formula

6.2 Step wise procedure for calculating the

percentage of lime and fly ash required for

stabilization of any black cotton

70

7. CONCLUSIONS 7.1 conclusion

7.2 future scope of project 72

8. REFERENCES 8.1 Books

8.2 Technical research papers 75


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Chapter 1

INTRODUCTION


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INTRODUCTION

Road needs good quality paving material having adequate strength and durability

characteristics. Subgrade soil is an integral part of the road pavement from beneath. The

subgrade soil and its properties are important in the design of pavement structure. The

main function of the subgrade is to give support to the pavement. And for this, the

subgrade should possess sufficient stability under adverse climate and loading condition.

In developing countries like India the biggest handicap to provide a complete network of

road system is its limited financial availability to build road by the conventional methods.

The soils of north india are residual, derived from the underlying basalts. In the

semi-dry plateau, the regular (black-cotton soil) is clayey, rich in iron, but poor in

nitrogen and organic matter; it is moisture-retentive.

Therefore, there is a need to resort to one of the suitable methods of low cost road

construction. Under this circumstance use of locally available material after suitable

treatment is only solution to meet the growth demand of road constructions. The

construction cost can be considerably decreased by selecting local materials including

local soils for the construction of the lower layers of the pavement. If the stability of the

local soil is not adequate for supporting wheel loads, the properties can be improved by

soil stabilization techniques. The principle of soil stabilized road construction involves

the effective utilization of local soil and other suitable stabilizing agent. Therefore the

first and foremost task is to characterize the locally available soil and after proper

assessment, suitable treatment is to be provided, if required.

Soil stabilization is any process which improves the physical properties of a soil,

such as increasing the shear strength, bearing capacity and the resistance to erosion, dust

formation, or frost heaving. The stabilization methods used are divided into mechanical,

chemical, and electrochemical methods. Mechanical methods are those in which the

compaction or bulk density is increased by dynamic or vibro-

compaction. Electrochemical methods of stabilization involve the reduction of water

content by electro-osmosis. Chemical stabilization is one of the effective stabilization

techniques.


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Chapter 2

LITERATURE REVIEW


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2.1 Black cotton soil

Black cotton soils are inorganic clays of medium to high compressibility and form

a major soil group in Maharashtra. They are characterized by high shrinkage and swelling

properties. Because of its high swelling and shrinkage characteristics, the Black cotton

soil has been a challenge to the highway engineers. The Black cotton soil is very hard

when dry, but loses its strength completely when in wet condition. It is observed that on

drying, the black cotton soil develops cracks of varying depth. As a result of wetting and

drying process, vertical movement takes place in the soil mass. All these movements lead

to failure of pavement, in the form of settlement, heavy depression, cracking and

unevenness.

The roads laid on Black cotton soil (BC soil) bases develop undulations at the

road surface due to loss of strength of the sub grade through softening during monsoon.

Around 40 to 60% of the Black cotton soil (BC soil) has a size less than 0.001 mm. At the

liquid limit, the volume change is of the order of 200 to 300% and results in swelling

pressure as high as 8 kg/cm2/ to 10 kg/cm

2. As such Black cotton soil (BC soil) has very

low bearing capacity and high swelling and shrinkage characteristics. Due to its peculiar

characteristics, it forms a very poor foundation material for road construction. Soaked

laboratory CBR values of Black Cotton soils are generally found in the range of 2 to 4%.

Due to very low CBR values of Black cotton soil (BC soil), excessive pavement thickness

is required for designing for flexible pavement.

Prof. katti has studied 13 black cotton soils, most of them from Maharashtra state.

The studies conducted on these soils were consistency, density, swelling pressure,

consolidation, shear, permeability, thixotropic property and effect of inorganic chemicals

etc.

2.2 Problems associated with black cotton soil as subgrade

There are two major problems associated with black cotton soil viz problems arising due

to water saturation and design problems in black cotton soil. They are described below.

A) Problems Arising out of Water Saturation


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It is a well-known fact that water is the worst enemy of road pavement,

particularly in expansive soil areas. Water penetrates into the road pavement from three

sides viz. top surface, side berms and from sub grade due to capillary action.

It has been found during handling of various road investigation project

assignments for assessing causes of road failures that water has got easy access into the

pavement. It saturates the sub grade soil and thus lowers its bearing capacity, ultimately

resulting in heavy depressions and settlement. In the base course layers comprising of

Water Bound Macadam (WBM), water lubricates the binding material and makes the

mechanical interlock unstable. In the top bituminous surfacing, raveling, stripping and

cracking develop due to water stagnation and its seepage into these layers.

B) Design Problems in Black cotton soils

In India, CBR method developed in USA is generally

used for the design of crust thickness. This method

stipulates that while determining the CBR values in the

laboratory and in the field, a surcharge weight of 15 kg

and 5 kg per 62 mm and 25 mm thickness respectively

should be used to counteract the swelling pressure of

Black cotton soils (BC soils). BC soils produce swelling

pressure in the range of 20-80 tons/m2 and swelling in

the range of 10-20%.Therefore, CBR values obtained are

not rational and scientific modification is required for determining CBR values of

expansive soil. Having heavy-duty traffic of 4500 commercial vehicles per day as

generally found on our National Highways and taking CBR value of 2%, total crust

thickness of flexible pavement works out to 830 mm which is practically an impossible

preposition. It is felt that CBR design curves require modification for expansive soils. If

heavy traffic intensity of 4500 commercial vehicles per day is assumed, crust thickness of

rigid pavement works out approximately 300-320 mm, which is about one third of

thickness needed for flexible pavement.


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2.3 Stabilization of subgrade soil

Soil stabilization is any process which improves the physical properties of a soil,

such as increasing the shear strength, bearing capacity and the resistance to erosion, dust

formation, or frost heaving. The stabilization methods used are divided into mechanical,

chemical, and electrochemical methods. Mechanical methods are those in which the

compaction or bulk density is increased by dynamic or vibro-

compaction. Electrochemical methods of stabilization involve the reduction of water

content by electro-osmosis. Chemical stabilization is one of the effective stabilization

techniques.

2.4 Lime stabilization

Several investigations were done to evaluate the soil stabilization process using lime

[either CaO or Ca(OH)2]. Lime stabilization involves the formation of strong bonds

between the clay minerals and other soil particles and is therefore ineffective in granular

soils. Three processes appear to be operative: (1) rapid replacement of exchangeable

cations by calcium with increased interparticle bonding and a more flocculated fabric; (2)

slower attack on the edges of the clay minerals by alkaline solutions in which the

solubility of silicon is increased, with the possible formation of new silicates similar to

those in cement; and (3) crystallization of calcite to form additional interparticle bridges.

Prof katti studied the effect of lime on unconfined compressive strength of 13 black

cotton soils and found that the optimum lime content for various soils fell in the range of

4 to 10 % and appeared to shift to higher percentages with an increase in curing time. A 2

to 4 % addition of lime produced little gain in strength over time.

According to Dr. K. R. Arora, the amount of lime required for stabilization varies

between 2 to 10 % of the soil. He has stated the following amount as a rough guide

(i) 2 to 5 % for clay gravel material having less than 50% of silt clay fraction

(ii) 5 to 10% for soil with more than 50% of silt – clay fraction

(iii)For soil having particle size intermediate between (i) and (ii) above, the quantity

of lime required is between 3 to 7%

(iv) About 10 % for heavy clays used as bases and sub bases.


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2.4.1 Qubain et al. (2000) incorporated the benefits of sub-grade lime stabilization, for the

first time, into the design of a major interstate highway pavement in Pennsylvania. The

project comprised widening and complete reconstruction of 21 Km of the Pennsylvania

turnpike in somerset-county. Field explorations indicated that the sub-grade is fairly

homogeneous and consists primarily of medium to stiff clayey soils. To safeguard against

potential softening due to rain, lime modification has been traditionally utilized as a

construction expedience for highway project with clayey sub-grade. Lime improves the

strength of clay by three mechanisms: hydration, flocculation, and cementation. The first

and second mechanisms occur almost immediately upon introducing the lime, while the

third is a prolonged effect. Qubain et al. investigated the first and second mechanisms.

Laboratory tests were performed to accurately capture the immediate benefits of lime

stabilization for design. Both treated and natural clayey samples were subjected to

resilient modulus and California bearing ratio testing. To prevent cementation, the lime-

treated specimens were not allowed to cure. Nevertheless, they showed significant

increase in strength, which, when incorporated into design, reduced the pavement

thickness and resulted in substantial savings.

2.4.2 Weber (2001) investigated the effect of both curing (storage) and degree of

compaction on the loss loam stabilized using different additives. He obtained the best

results under condition of moisture atmosphere storage. At the water storage condition,

the tempering of the stabilized specimens delayed due to the changing of pH-value in the

pores water. The reactivity of lime stabilized specimens was continuing under this water

storage condition. He noticed that the variation of compaction degree of the stabilized

specimens affected on the behavior of the stabilized specimens and the compaction at the

highest densities lead to brittle failure behavior.

2.4.3 Ismail (2004) studied materials and soils derived from the Feuerletten (Keuper) and

Amaltheenton (Jura) formations along the new Nuernberg-Ingolstadt railway line

(Germany).

His work included petrological, mineralogical studies and scanning electron microscope

analysis. Ismail treated and stabilized these materials related to road construction using

lime (10%), cement (10%), and lime/cement (2.5%/7.5%). He determined consistency


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limits, compaction properties, and shear- and uniaxial-strength. Ismail concluded that by

increasing the optimum moisture content (%) of the treated soils mixtures, the maximum

dry density decreased. The cohesion and the friction angle of the improved materials

increased for all the treated mixtures. In case of the lime-treated materials, the cohesion

decreased by curing time. For Feuerletten materials, uniaxial strength increased strongly

using lime and cement together. For Amaltheenton, uniaxial strength increased strongly

with cement alone. He also noticed that the loss of weight during freezing and thawing

test was low and depended on the material type.

2.4.4 Ampera & Aydogmust (2005) treated Chemnitz clayey soil [according to American

Association of State Highway and Transportation Officials (AASHTO)] using lime

(2, 4, and 6%) and cement (3, 6, and 9%). They conducted compaction, unconfined

compressive strength, and direct shear tests on untreated and treated specimens. They

concluded that the strength of cement treated soil was generally greater than the strength

of lime treated soil. They also reported that lime stabilization is more suitable for the

clayey soils. The relationships determined from direct shear tests were similar to those

determined from unconfined compressive strength tests. Thus, the results of shear

strength tests showed a similar trend to that of the unconfined compressive strength tests.

2.4.5 Venkata Swamy, B studied on Stabilisation of Black Cotton Soil by Lime Piles.

Lime stabilization of clays in field is achieved by shallow mixing of lime and soil or by

deep stabilization technique. Shallow stabilization involves scarifying the soil to the

required depth and lime in powder or slurry form is spread and mixed with the soil using

a rotovator. The use of lime as deep stabilizer has been mainly restricted to improve the

engineering behaviour of soft clays Deep stabilization using lime can be divided in three

main groups: lime columns, lime piles and lime slurry injection.

2.5 Fly ash stabilization

Various studies were carried out in several countries like USA, Japan, India, etc to verify

the soil stabilization process using fly ash either class F or class C and other off

specification= types of fly ash. Some Fly ash by itself has cementatious value but in the

presence of moisture it reacts chemically and forms cementatious compounds and

attributes to the improvement of strength and compressibility characteristics of soils. It

http://etd.ncsi.iisc.ernet.in/browse?type=author&value=Venkata+Swamy%2C+B


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has a long history of use as an engineering material and has been successfully employed

in geotechnical applications.

2.5.1Edil et al. (2002) conducted a field evaluation of several alternatives for construction

over soft sub-grade soils. The field evaluation was performed along a 1.4 Km segment of

Wisconsin state highway 60 and consisted of several test sections. By products such as fly

ash, bottom ash, foundry slag, and foundry sand were used. A class C fly ash was used for

one test section. Unconfined compression testing showed that 10% fly ash was sufficient

to provide the strength necessary for the construction on the sub-grade. Data were

obtained before and after fly ash placement by testing undisturbed samples in the

laboratory and by using a soil stiffness gauge (SSG) and a dynamic cone penetrometer

(DCP) in the field. Unconfined compressive strength, soil stiffness, and dynamic cone

penetration of the native soil before fly ash placement ranged between 100 - 150 KPa, 4 -

8 MN/m², and 30 -90 mm/blow, respectively. After fly ash addition, the unconfined

compressive strength reached as high as 540 KPa, the stiffness ranged from 10 to 18

MN/m2, and the Dynamic Penetration Index (DPI) was less variable and ranged between

10 and 20 mm/blow. CBR of 32% was reported for the stabilized sub-grade, which is

rated as “good” for sub-base highway construction. CBR of the untreated sub-grade was

3%, which is rated as “very poor”.

2.5.2 Acosta et al. (2002) estimate the self-cementing fly ashes as a sub-grade stabilizer

for Wisconsin soils. A laboratory-testing program was conducted to evaluate the

mechanical properties of fly ash alone, and also to evaluate how different fly ashes can

improve the engineering properties of a range of soft sub-grade soil from different parts

of Wisconsin.

Seven soils and four fly ashes were considered for the study. Soil samples were prepared

with different fly ash contents (i.e., 0, 10, 18, and 30%), and compacted at different soil

water contents (optimum water content, 7% wet of optimum water content “approximate

natural water content of the soil”, and a very wet conditions “9 to 18% wet of optimum

water content”). Three types of tests were performed: California bearing ratio test,

resilient modulus test, and unconfined compressive strength test. The soils selected

represented poor sub-grade conditions with CBR ranging between 0 and 5 in their natural


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condition. A substantial increase in the CBR was achieved when soils were mixed with

fly ash. Specimens prepared with 18% fly ash content and compacted at the optimum

water content show the best improvement, with CBR ranging from 20 to 56. Specimens

prepared with 18% fly ash and compacted at 7% wet of optimum water content showed

significant improvement compared to the untreated soils, with CBR ranging from 15 to 31

(approximately an average CBR gain of 8 times). On the other hand, less improvement

was noticed when the specimens were prepared with 18% fly ash and compacted in very

wet condition (CBR ranging from 8 to 15).

Soil-fly ash mixtures prepared with 18% fly ash content and compacted at 7% wet of

optimum water content had similar or higher modulus than untreated specimens

compacted at optimum water content. Resilient modulus of specimens compacted in

significantly wet conditions, in general, had lower module compared to the specimen

compacted at optimum water content. The resilient modulus increased with increasing the

curing time. The resilient modulus of specimens prepared at 18% fly ash content and

compacted at 7% wet of optimum water content was 10 to 40% higher after 28 days of

curing, relative to that at 14 days of curing. Unconfined compressive strength of the soil-

fly ash mixtures increased with increasing fly ash content. Soil-fly ash specimens

prepared with 10 and 18% fly ash content and compacted 7% wet of optimum water

content had unconfined compressive strength that were 3 and 4 times higher than the

original untreated soil specimen compacted at 7% wet of optimum water content. CBR

and resilient modulus data was used for a flexible pavement design. Data developed from

stabilized soils showed that a reduction of approximately 40% in the base thickness could

be achieved when 18% fly ash is used to stabilize a soft subgrade.

2.5.3 Şenol et al. (2002) studied the use of self-cementing class C fly ash for the

stabilization of soft sub-grade of a city street in cross plains, Wisconsin, USA. Both

strength and modulus based approaches were applied to estimate the optimum mix design

and to determine the thickness of the stabilized layer. Stabilized soil samples were

prepared by mixing fly ash at three different contents (12, 16, and 20%) with varying

water contents. The samples were subjected to unconfined compression test after 7 days

of curing to develop water content strength relationship. The study showed that the

engineering properties, such as unconfined compressive strength, CBR, and resilient


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modulus increase substantially after fly ash stabilization. The stabilization process is

construction sensitive and requires strict control of moisture content. The impact of

compaction delay that commonly occurs in field construction, was evaluated, one set of

the samples was compacted just after mixing with water, while the other set after two

hours. The results showed that the strength loss due to compaction delay is significant

and, therefore, must be considered in design and construction.

CBR and resilient modulus tests were conducted and used to determine the thickness of

the stabilized layer in pavement design.

2.5.4 Thomas & White (2003) used self-cementing fly ashes (from eight different fly ash

sources) to treat and stabilize five different soil types (ranging from ML to CH) in Iowa

for road construction applications. They investigated various geotechnical properties

(under different curing-conditions) such as compaction, qu-value, wet/dry and

freeze/thaw durability, curing time effect, and others. They reported that Iowa self-

cementing fly ashes can be an effective means of stabilizing Iowa soil. Unconfined

compressive strength, strength gain, and CBR-value of stabilized soils increased

especially with curing time. Soil-fly ash mixtures cured under freezing condition and

soaked in water slaked and were unable to be tested for strength. They also noticed that

stabilized paleosol exhibited an increase in the freeze/thaw durability when tested

according to ASTM C593, but stabilized Turin loess failed in the test.

2.5.5 Effect of Fly ash on expansive soil was studied by Erdal Cokca. Fly ash consists of

often hollow spheres of silicon, aluminium and iron oxides and unoxidized carbon. There

are two major classes of fly ash, class C and class F. The former is produced from

burning anthracite or bituminous coal and the latter is produced from burning lignite and

sub bituminous coal. Both the classes of fly ash are puzzolans, which are defined as

siliceous and aluminous materials. Thus Fly ash can provide an array of divalent and

trivalent cations (Ca2+, Al3+, Fe3+etc) under ionized conditions that can promote

flocculation of dispersed clay particles. Thus expansive soils can be potentially stabilized

effectively by cation exchange using fly ash. He carried out investigations using Soma

Fly ash and Tuncbilek fly ash and added it to expansive soil at 0-25%. Specimens with fly

ash were cured for 7days and 28 days after which they were subjected to Oedometer free


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swell tests. And his experimental findings confirmed that the plasticity index, activity and

swelling potential of the samples decreased with increasing percent stabilizer and curing

time and the optimum content of fly ash in decreasing the swell potential was found to be

20%. The changes in the physical properties and swelling potential is a result of

additional silt size particles to some extent and due to chemical reactions that cause

immediate flocculation of clay particles and the time dependent puzzolanic and self

hardening properties of fly ash and he concluded that both high –calcium and low calcium

class C fly ashes can be recommended as effective stabilizing agents for improvement for

improvement of expansive soils.

2.5.6 Pandian et.al. (2002) studied the effect of two types of fly ashes Raichur fly ash

(Class F) and Neyveli fly ash (Class C) on the CBR characteristics of the black cotton

soil. The fly ash content was increased from 0 to 100%. Generally the CBR/strength is

contributed by its cohesion and friction. The CBR of BC soil, which consists of

predominantly of finer particles, is contributed by cohesion. The CBR of fly ash, which

consists predominantly of coarser particles, is contributed by its frictional component.

The low CBR of BC soil is attributed to the inherent low strength, which is due to the

dominance of clay fraction. The addition of fly ash to BC soil increases the CBR of the

mix up to the first optimum level due to the frictional resistance from fly ash in addition

to the cohesion from BC soil. Further addition of fly ash beyond the optimum level causes

a decrease up to 60% and then up to the second optimum level there is an increase. Thus

the variation of CBR of fly ash-BC soil mixes can be attributed to the relative

contribution of frictional or cohesive resistance from fly ash or BC soil respectively. In

Neyveli fly ash also there is an increase of strength with the increase in the fly ash

content, here there will be additional puzzolonic reaction forming cementitious

compounds resulting in good binding between BC soil and fly ash particles.

2.5.7 A similar study was carried out by Phanikumar and Sharma and the effect of fly ash

on engineering properties of expansive soil through an experimental programme. The

effect on parameters like free swell index (FSI), swell potential, swelling pressure,

plasticity, compaction, strength and hydraulic conductivity of expansive soil was studied.

The ash blended expansive soil with fly ash contents of 0, 5, 10, 15 and 20% on a dry


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weight basis and they inferred that increase in fly ash content reduces plasticity

characteristics and the FSI was reduced by about 50% by the addition of 20% fly ash. The

hydraulic conductivity of expansive soils mixed with fly ash decreases with an increase in

fly ash content, due to the increase in maximum dry unit weight with an increase in fly

ash content. When the fly ash content increases there is a decrease in the optimum

moisture content and the maximum dry unit weight increases. The effect of fly ash is akin

to the increased compactive effort. Hence the expansive soil is rendered more stable. The

undrained shear strength of the expansive soil blended with fly ash increases with the

increase in the ash content.

2.6 Lime + different materials for stabilization

2.6.1 Rice husk ash is apotentially useful waste, which can be used with lime to improve

physical, engineering and strength properties of black cotton soil. The cementitious

compounds formed during pozzolanic reactions acts as a bonding material for the soil

particles. The plasticity characteristics of black cotton soil are improved upon addition of

RHA and lime. The PI of soil decreses to 7.93 percent from 35.79 percent on addition of

10% RHA and 6% lime. With addition of RHA and lime to BC soil, the MDD decreases

and OMC increases. Also, the optimum CBR was found for BC soil-10% RHA-6%lime

mixes.

2.6.2 Eggshell Powder (ESP) has not been used as a stabilizing material; however, it

could be a supplement for industrial lime. The effect of eggshell powder on the stabilizing

potential of lime on an expansive clay soil has been studied by O.O. Amu. Tests were

carried out to determine the optimal quantity of lime and the optimal percentage of lime-

ESP combination; the optimal quantity of lime was gradually replaced with suitable

amount of eggshell powder. The lime stabilized and lime-ESP stabilized mixtures were

subjected to engineering tests.

The optimal percentage of lime-ESP combination was attained at a 4% ESP + 3% lime,

which served as a control.


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2.7 lime + fly ash stabilization

Several works were done to treat and stabilize various types of the problematic soils using

lime and fly ash together

2.7.1 Nalbantoglu & Gucbilmez (2002) studied the utilization of an industrial waste in

calcareous expansive clay stabilization, where the calcareous expansive soil in Cyprus

had caused serious damage to structures. High-quality Soma fly ash admixture has been

shown to have a tremendous potential as an economical method for the stabilization of the

soil. Fly ash and lime-fly ash admixtures reduce the water absorption capacity and the

compressibility of the treated soils. Unlike some of the previously published research, an

increase in hydraulic conductivity of the treated soils was obtained with an increase in

percent fly ash and curing time. X-ray diffractograms indicate that pozzolanic reactions

cause an alteration in the mineralogy of the treated soils, and new mineral formations

with more stable silt-sand-like structures are produced. The study showed that, by using

cation exchange capacity (CEC) values, with increasing percentage of fly ash and curing

time, soils become more granular in nature and show higher hydraulic conductivity

values.

2.7.2 Zhang & Cao (2002) conducted an experimental program to study the individual

and admixed effects of lime and fly ash on the geotechnical characteristics of expansive

soil. Lime and fly ash were added to the expansive soil at 4 - 6% and 40 - 50% by dry

weight of soil, respectively. Testing specimens were determined and examined in

chemical composition, grain size distribution, consistency limits, compaction, CBR, free

swell and swell capacity. The effect of lime and fly ash addition on a reduction of the

swelling potential of an expansive soil texture was reported. It was revealed that a change

of expansive soil texture takes place when lime and fly ash are mixed with expansive soil.

Plastic limit increases by mixing lime and liquid limit decreases by mixing fly ash, and

this decreased plasticity index. As the amount of lime and fly ash is increased, there is an

apparent reduction of maximum dry density, free swell, and of swelling capacity under 50

KPa pressure and a corresponding increase in the percentage of coarse particles, optimum

moisture content, and in the CBR value. They concluded that the expansive soil can be

successfully stabilized by lime and fly ash.


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2.7.3 Beeghly (2003) evaluated the use of lime together with fly ash in stabilization of

soil subgrade (silty and clayey soils) and granular aggregate base course beneath the

flexible asphalt layer or rigid concrete layer. He reported that lime alone works well to

stabilize clay soils but a combination of lime and fly ash is beneficial for lower plasticity

(higher silt content) soils. He noticed that both unconfined compressive strength and CBR

values of treated stabilized soils (moderate plasticity “PI < 20” and high silt content “i.e.

> 50%”) with lime and fly ash together are higher than the values with lime alone.

Beeghly (2003) also concluded that the capillary soak of the stabilized specimens led to a

loss of unconfined compressive strength (15 - 25%). Finally, lime/fly ash admixtures

resulted in cost savings by increment material cost by up to 50% as compared to Portland

cement stabilization.

2.7.4 Parson & Milburn (2003) conducted a series of tests to evaluate the stabilization

process of seven different soils (CH, CH, CH, CL, CL, ML, and SM) using lime, cement,

class C fly ash, and an enzymatic stabilizer. They determined Atterberg limits and

unconfined compressive strengths of the stabilized soils before and after carrying out of

durability tests (freeze/thaw, wet/dry, and leach testing). They reported that lime and

cement stabilized soils showed better improvement compared to fly ash treated soils. In

addition, the enzymatic stabilizer did not strongly improve the soils compared to the other

stabilizing agents (cement, lime, and fly ash).

2.7.5 Faqir Chand has found that hydrated lime in the range of 5 to 8 % and fly ash

between 10 to 15% brings remarkable improvement in the engineering characteristics of

BC soils. However, excess of lime more than 8% reduces the strength and weakens the

soil iniatial properties due to liberation of excess heat during hydration. Therefore, 6%

lime is taken as optimum level of cement content with fly ash 15%.

2.7.6 Niroj Mishra has studied the engineering properties of only soil, soil + fly ash@

(20,30 and 40%), soil + lime@(2,3,4%) and soil + fly ash@(20,30%)+lime@(2,3,4%) .

He observed that maximum CBR value has been obtained for 70:30:3 mix of soil, fly ash

and lime


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Through our literature review, it was found that lime and fly ash alone, lime in

combination with other materials and lime + fly ash can be used for subgrade

stabilization. However, the study in the area of lime + fly ash stabilization is unreliable,

unauthentic. Hence, there borne a need to make a extensive study on lime+fly ash

stabilization.

2.8 Materials and Types

2.8.1 Lime

Lime can be used either to modify some of the physical properties and thereby improve

the quality of soil or to transform the soil into a stabilized mass, which increases its

strength and durability. The amount of lime additive will depend upon either the soil to be

modified or stabilized. Generally, lime is suitable for clay soils with PI ≥ 20% and > 35%

passing the

No.200 sieve (0.074 mm). Lime stabilization is applied in road construction to improve

subbase and sub-grades, for railroads and airports construction, for embankments, for soil

exchange in unstable slopes, for backfill, for bridge abutments and retaining walls, for

canal linings, for improvement of soil beneath foundation slabs, and for lime piles. Lime

stabilization includes the use of burned lime products, quicklime and hydrated lime i.e

oxides and hydroxides, respectively, or lime by-products .The improvement of the

geotechnical properties of the soil and the chemical stabilization process using lime take

place through two basic chemical reactions as follow:

I) Short-term reactions including cation exchange and flocculation, where lime is a strong

alkaline base which reacts chemically with clays causing a base exchange. Calcium ions

(divalent) displace sodium, potassium, and hydrogen (monovalent) cations and change the

electrical charge density around the clay particles. This results in an increase in the

interparticle attraction causing flocculation and aggregation with a subsequent decrease in

the plasticity of the soils.

II) Long-term reaction including pozzolanic reaction, where calcium from the lime reacts

with the soluble alumina and silica from the clay in the presence of water to produce

stable calcium silicate hydrates (CSH), calcium aluminate hydrates (CAH), and calcium


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aluminosilicate hydrates (CASH) which generate long-term strength gain and improve the

geotechnical properties of the soil. The use of lime for soil stabilization is either in the

form of quicklime (CaO) or hydrated lime Ca(OH)2. Agricultural lime or other forms of

calcium carbonate, or carbonated lime, will not provide the necessary reactions to

improve sub-grade soils mixed with lime.

In the present study, hydrated lime was used. Hydrated lime is calcium hydroxide,

Ca (OH)2. It is produced by reacting quicklime (CaO) with sufficient water to form a

white powder. This process is referred to as slaking.

High calcium quicklime + water Hydrated lime + Heat

CaO + H2O Ca(OH)2 + Heat

Hydrated lime is used in most of the lime stabilization applications. Quicklime represents

approximately 10% of the lime used in lime stabilization process. Other forms of lime

sometimes used in lime stabilization applications are dehydrated dolomitic lime,

monohydrated dolomitic lime, and dolomitic quicklime. Calcium oxide may be more

effective in some cases, however the quick lime will corrosively attack equipment. The

Addition of the hydrated lime Ca(OH)2, in situ or in laboratory, is either as slurry formed

by the slaking of quicklime, or as dry form. In the present study, the addition of the

hydrated lime is in a dry form. In general, all lime treated fine-grained soils exhibit

decreased plasticity, improved workability and reduced volume change characteristics.

However, not all soils exhibit improved strength characteristics. It should be emphasized

that the properties of soil-lime mixtures are dependent on many factors such as soil type,

lime type, lime percentage, and curing conditions like time, temperature, and moisture.

2.8.2 Fly ash

Fly ash is a by-product of burning coal at electric power plants. It is a fine residue

composed of unburned particles that solidifies while suspended in exhaust gases. Fly ash

is carried off in stack gases from a boiler unit, and is collected by mechanical methods or

electrostatic precipitators. Fly ash is composed of fine spherical silt size particles in the

range of 0.074 to 0.005 mm. Fly ash collected using electrostatic precipitators usually has

finer particles than fly ash collected using mechanical precipitators. Fly ash is one of the

most useful and versatile industrial by-products. When geotechnical Engineers are faced


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with clayey or expansive soils, the engineering properties of those soils may need to be

improved to make them suitable for construction. Waste materials such as fly ash or

pozzolanic materials are a source of silica and alumina with high surface area has been

used for soil improvement. Fly ash is generated in huge quantities as a by-product of

burning coal at electric power plants . The potential for using fly ash in soil stabilization

has increased significantly in many countries since it is environmentally safe.

Fly ash is classified into two classes: F and C. Class F fly ash which is not self-cementing

fly ash is produced from burning anthracite and bituminous coals and contains small

amount of lime (CaO) to produce cementitious products. An activator such as Portland

cement or lime must be added. This fly ash has siliceous and aluminous material, which

itself possesses little or no cementitious value but it reacts chemically with lime at

ordinary temperature to form cementitious compounds.

Class C fly ash which is self-cementing fly ash is produced from lignite and sub-

bituminous coals and usually contains significant amount of lime .This type (class C) is

self-cementing because it contains a high percent of calcium oxide (CaO) ranging from

20 to 30%.

Formation of cementitious material by the reaction of lime with the pozzolans (Al2O3,

SiO2, and Fe2O3) in the presence of water is known as hydration of fly ash. The hydrated

calcium silicate or calcium aluminate as cementitious material, can join inert materials

together. The pozzolanic reactions for soil stabilization are as follow :

CaO + H2O Ca(OH)2 + Heat

Ca (OH)2 Ca ++

+ 2 (OH)

Ca ++ + 2 (OH) + SiO2 CSH “Calcium silicate hydrate“

(silica) (gel)

Ca ++

+ 2 (OH) + Al2O3 CAH “Calcium aluminate hydrate”

(alumina) (fibrous)

In case of the class C fly ash, the lime present in the fly ash reacts with the siliceous and

aluminous materials in the fly ash. A similar reaction can occur in class F fly ash, but

lime must be added because of the low lime content of the fly ash class F.


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2.8.3 Black cotton soil

Black cotton soils are inorganic clays of medium to high compressibility and form

a major soil group in Maharashtra. They are characterized by high shrinkage and swelling

properties. Because of its high swelling and shrinkage characteristics, the Black cotton

soil has been a challenge to the highway engineers. The Black cotton soil is very hard

when dry, but loses its strength completely when in wet condition. It is observed that on

drying, the black cotton soil develops cracks of varying depth.The roads laid on Black

cotton soil (BC soil) bases develop undulations at the road surface due to loss of strength

of the sub grade through softening during monsoon. Around 40 to 60% of the Black

cotton soil (BC soil) has a size less than 0.001 mm. At the liquid limit, the volume change

is of the order of 200 to 300% and results in swelling pressure as high as 8 kg/cm2/ to 10

kg/cm2. Average Plasticity Index of black cotton soil was found as 60 %

As such Black cotton soil (BC soil) has very low bearing capacity and high

swelling and shrinkage characteristics. Due to its peculiar characteristics, it forms a very

poor foundation material for road construction. Soaked laboratory CBR values of Black

Cotton soils are generally found in the range of 2 to 4%. Due to very low CBR values of

Black cotton soil (BC soil), excessive pavement thickness is required for designing for

flexible pavement.


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Chapter 3

OBJECTIVE OF THE PROJECT


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OBJECTIVES OF THE PROJECT

As stated above, road construction in black cotton soil area is difficult and hence

there is need of increasing the strength of black cotton soil as a subgrade for road. Thus,

the soil properties can be improved by soil stabilization techniques. Thus, the problem

statement of the project is to stabilize the subgrade soil(black cotton soil) using a suitable

stabilizer.

Chemical stabilizers like cement, lime are added to soil to improve soil strength,

stress-strain behavior, and durability etc.

Thus, objectives of the project are as follows

1. To study the properties of black cotton soil available locally.

2. To check the suitability of fly ash-lime combined mixture as a stabilizer for the

black cotton soil in Maharashtra

3. To obtain the correct proportion of soil, fly ash and lime to be mixed for

stabilization.


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Chapter 4

METHODOLOGY


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METHODOLOGY

4.1 Properties of black cotton soil

Locally available fine grained black cotton soil from nearby site was acquired and fly ash

from Nashik thermal power station was procured. The necessary experiments to be

carried out on BC soil are sieve analysis, Standard proctor test, Atterberg‟s limits test,

Differential swell test and unconfined compressive test.

The procedures for tests were according to IS codes, which are described below.

4.1.1 Sieve analysis:

The portion of the soil sample retained on 4.75-mm IS Sieve, selected for test, was

weighed and the mass recorded As the mass of the sample uncorrected for hygroscopic

moisture. The quantity of the soil sample taken shall depend on the maximum particle

size contained in the soil. The sample was separated into various fractions by sieving

through the Indian Standard Sieves, 100mm, 75mm,19mm & 4.75mm. While sieving

through each sieve, the sieve was agitated so that the sample rolls in irregular motion over

the Sieve. Any particles may be tested to see if they will fall through but they shall not be

pushed through. The material from the sieve may be rubbed, if necessary, with the rubber

pestle in the mortar taking care to see that individual soil particles are not broken and re-

sieved to take sure that only individual particles are retained. The quantity taken each

time for sieving on each sieve was such that the maximum weight of material retained on

each sieve at the completion of sieving should be noted.

4.1.2 Hydrometer analysis:

We took the fine soil from the bottom pan of the sieve set, place it into a beaker, and add

125 mL of the dispersing agent (sodium hexametaphosphate (40 g/L)) solution. Stirred

the mixture until the soil is thoroughly wet. Let the soil soak for at least ten minutes.

While the soil is soaking, add 125mL of dispersing agent into the control cylinder and it

was filled with distilled water to the mark. Take threading at the top of the meniscus

formed by the hydrometer stem and the control solution. A reading less than zero is

recorded as a negative


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(-) correction and a reading between zero and sixty is recorded as a positive (+)

correction. This reading is called the zero correction. The meniscus correction is the

difference between the top of the meniscus and the level of the solution in the control jar

(Usually about +1).

Shake the control cylinder in such a way that the contents are mixed thoroughly. Insert

the hydrometer and thermometer into the control cylinder and note the zero correction

and temperature respectively.

Transferred the soil slurry into a mixer by adding more distilled water, if necessary, until

mixing cup is at least half full. Then mix the solution for a period of two minutes.

Immediately transfer the soil slurry into the empty sedimentation cylinder. Add distilled

water up to the mark. Cover the open end of the cylinder with a stopper and secure it with

the palm of your hand. Then turn the cylinder upside down and back upright for a period

of one minute. (The cylinder should be inverted approximately 30 times during the

minute.) Set the cylinder down and record the time. Remove the stopper from the

cylinder. After an elapsed time of one minute and forty seconds, very slowly and

carefully insert the hydrometer for the first reading.(Note: It should take about ten

seconds to insert or remove the hydrometer to minimize any disturbance, and the release

of the hydrometer should be made as close to the reading depth as possible to avoid

excessive bobbing). The reading is taken by observing the top of the meniscus formed by

the suspension and the hydrometer stem. The hydrometer is removed slowly and placed

back into the control cylinder. Very gently spin it in control cylinder to remove any

particles that may have adhered. Take hydrometer readings after elapsed time of 2 and 5,

8, 15, 30, 60 Minutes and 24 hours.

4.1.3 Standard proctor test:

A 3-kg sample of air dried soil passing the 20 mm IS test sieve shall be taken. The sample

shall be mixed thoroughly with a suitable amount of water depending on the soil type.

The mould, with base plate attached, shall be weighed to the nearest 1 g (ml). The mould

shall be placed on a solid base, such as a concrete floor or plinth and the moist soil shall

be compacted into the mould, with the extension attached, in three layers of

approximately equal mass, each layer being given 25 blows from the 2*6-kg rammer

dropped from a height of 310 mm above the soil. The blows shall be distributed


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uniformly over the surface of each layer. The operator shall ensure that the tube of the

rammer is kept clear of soil so that the rammer always falls freely. The amount of soil

used shall be sufficient to fill the mould, leaving not more than about 6 mm to be struck

off when the extension is removed. The extension shall be removed and the compacted

soil shall be leveled off carefully to the top of the mould by means of the straightedge.

The mould and soil shall then be weighed. The compacted soil specimen shall be

removed from the mould and placed on the mixing tray. The water content of a

representative 3mm of the specimen shall be determined as in IS: 2720 (Part 11 ). The

remainder of the soil specimen shall be broken up, rubbed through the 20-mm IS test

sieve, and then mixed with the remainder of the original sample. Suitable increments of

water shall be added successively and mixed into the sample, and the above procedure

shall be repeated for each increment of water added. The total number of determinations

made shall he at least five, and the range of moisture contents should be such that the

optimum moisture content, at which the maximum dry density occurs, is within that

range.

4.1.4 Liquid limit test:

About 120 g of the soil sample passing 425-micron IS Sieve shall be mixed thoroughly

with distilled water in the evaporating dish or on the flat glass plate to form a uniform

paste. The paste shall have a consistency that will require 30 to 35 drops of the cup to

cause the required closure of the standard groove. In the case of clayey soils, the soil

paste shall be left to stand for a sufficient time (24 hours) so as to ensure uniform

distribution of moisture throughout the soil mass. The soil should then be re-mixed

thoroughly before the test. A portion of the paste shall be placed in the cup above the spot

where the cup rests on the base, squeezed down and spread into position, with as few

strokes of the spatula as possible and at the same time trimmed to a depth of one

centimeter at the point of maximum thickness, returning the excess soil to the dish. The

soil in the cup shall be decided by firm strokes of the grooving tool along the diameter

through the centre line of the cam follower so that a clean, sharp groove of the proper

dimensions is formed.

The cup shall be fitted and dropped by turning the crank at the rate of two revolutions per

second until the two halves of the soil cake come in contact with bottom of the groove


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along a distance of about 12 mm. This length shall be measured with the end of the

grooving tool or a ruler. The number of drops required to cause the groove close for the

length of 12 mm shall be recorded. A little extra of the soil mixture shall be added to the

cup and mixed with the soil in the cup. The pat shall be made in the cup and the test

repeated. In no case shall dried soil be added to the thoroughly mixed soil that is being

tested. The procedure shall be repeated until two consecutive runs give the same under of

drops for closure of the groove. A representative slice of soil approximately the width of

the spatula, extending from about edge to edge of the soil cake at right angle to the groove

and including that portion of the groove in which the soil flowed together, shall be taken

in a suitable container and its moisture content expressed as a percentage of the oven dry

weight otherwise determined as described in IS : 2720 ( Part 2 )-1973*. The remaining

soil in the cup shall be transferred to the evaporating dish and the cup and the grooving

tool cleaned thoroughly. The operations shall be repeated for at least three more

additional trails (minimum of four in all), which the soil collected in the evaporating dish

or flat glass plate, to with sufficient water has been added to bring the soil to a more fluid

condition. In each case the number of blows shall be recorded and the moisture content

determined as before. The specimens shall be of such consistency that the number of

drops required to ~close the groove shall be not less than 15 or more than 35 and the

points on the flow curve are evenly distributed in this range. The test should proceed from

the drier (more drops) to the wetter ( less drops ) condition of the soil. The test may also

be conducted from the wetter to the drier condition provided drying is achieved by

kneading the wet soil and not by adding dry soil. „A flow curve‟ shall be plotted on a

semi-logarithmic graph representing water content on the arithmetical scale and the

number of drops on the logarithmic scale. The flow curve is a straight line drawn as

nearly as possible through the four or more plotted points. The moisture content

corresponding to 25 drops as read from the curve shall be rounded off to the nearest

whole number and reported as the liquid limit of the soil.

4.1.5 Plastic limit test:

The soil sample shall be mixed thoroughly with distilled water in an evaporating dish or

on the flat glass plate till the soil mass becomes plastic enough to be easily molded with

fingers. In the case of clayey soils the plastic soil mass shall be left to stand for a


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sufficient time (24 hours) to ensure uniform distribution of moisture throughout the soil.

A ball shall be formed with about 8 g of this plastic soil mass and rolled between the

fingers and the glass plate with just sufficient pressure to roll the mass into a thread of

uniform diameter throughout its length. The rate of rolling shall be between 80 and 90

strokes/min counting a stroke as one complete motion of the hand forward and back to the

starting position again. The rolling shall be done till the threads are of 3 mm diameter.

The soil shall then be kneaded together to a uniform mass and rolled again. This process

of alternate rolling and kneading shall be continued until the thread crumbles under the

pressure required for rolling and the soil can no longer be rolled into a thread. The

crumbling may occur when the thread has a diameter greater than 3 mm. This shall be

considered a satisfactory end point, provided the soil has been rolled into a thread 3 mm

in diameter immediately before. At no time shall an attempt be made to produce failure at

exactly 3 mm diameter by allowing the thread to reach 3 mm, then reducing the rate of

rolling or pressure or both, and continuing the rolling without further deformation until

the thread falls apart. The pieces of crumbled soil thread shall be collected in an air-tight

container and the moisture content determined as described in IS: 2720 (Part 2)-1973;

4.1.6 Shrinkage limit test:

Keep the specimen in suitable small dill and air-dry it. Then dry the specimen in the dish

to constant weight in an oven at 105 to 110°C. Remove the specimen from the oven and

smoothen the edges by sand papering. Brush off the soil dust from the specimen by a soft

paint brush. Place the specimen again in the cleaned dish and dry it in an oven to constant

weight. Cool the oven-dry specimen in a desiccators and weigh it with the dish.

Determine the oven-dry weight of the specimen.

4.1.7 Differential swell index:

Two 10 gm soil specimens of oven dry soil passing through 425-micron IS Sieve was

taken. Each soil specimen was poured in each of the two glass graduated cylinders of 100

ml capacity. One cylinder was then be filled with kerosene oil and the other with distilled

writer up to the 100 ml mark. After removal of entrapped air (by gentle shaking or stirring

with a: tglass rod), the soils in both the cylinders was allowed to settle. Sufficient time

was allowed for the soil sample to attain equilibrium state of volume without any further


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change in the volume of the soils. The final volume of soils in each of the cylinders was

read out.

The level of the soil in the kerosene graduated cylinder was read as the original volume

of the soil samples, kerosene being a non-polar liquid does not cause swelling of the soil.

The level of the soil in the distilled water cylinder was read as the free swell level. The

differential swell index of the soil is calculated as follows:

Differential swell in, percent

Where,

V d= the volume of soil specimen read from the graduated cylinder containing distilled

water,

Vk = the volume of soil specimen read from the graduated cylinder containing kerosene

4.2 Preparation of samples

Samples were prepared using a mould of circular cross-section of 36 mm diameter and

height 75 mm. The samples were casted at with their respective optimum moisture

content calculated by standard proctor test for every proportion. After the specimen was

formed, the ends were trimmed perpendicular to the long axis and removed from the

mould. Representative sample cuttings were obtained for the determination of unconfined

compressive strength test. The 9 proportions were casted as given in table below. 2

samples for each proportion were made.


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Lime in % Fly ash in % Soil in %

4 10 100

4 20 100

4 30 100

4 40 100

4 50 100

4 60 100

6 10 100

6 20 100

6 30 100

6 40 100

6 50 100

6 60 100

8 10 100

8 20 100

8 30 100

8 40 100

8 50 100

8 60 100

10 10 100

10 20 100


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10 30 100

10 40 100

10 50 100

10 60 100

12 10 100

12 20 100

12 30 100

12 40 100

12 50 100

12 60 100

14 10 100

14 20 100

14 30 100

14 40 100

14 50 100

14 60 100


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4.3 Curing of samples

Samples were cured for 7, 14 and 21 days. Samples were kept in plastic bags and covered

by wet gunny bags to retain the original moisture content.

4.4 Unconfined compressive strength test:

Unconfined compressive strength test on samples was done. The procedure for test is as

below:

The initial length, diameter and weight of the specimen shall be measured and the

specimen placed on the bottom plate of the loading device. The upper plate shall be

adjusted to make contact with the specimen. The deformation dial gauge shall be adjusted

to a suitable reading, preferably in multiples of 100. Force shall be applied so as to

produce axial strain at a rate of 0.5 to 2 percent per minute causing failure with 5 to 10.

The force reading shall be taken at suitable intervals of the deformation dial reading.

Compressive stress, shall be determined from the relationship: P/A

NOTE - Up to 6% axial strain force, readings may be taken at an interval of 0.5 mm of

the deformation dial reading. After 6% axial strain, the interval may be increased to 1.0

mm and, beyond 12% axial strain it may be increased even further. The specimen shall be

compressed until failure surfaces have definitely developed, or stress-strain curve is well

past its peak, or until axial strain of 20 percent is reached. The failure pattern shall be

sketched carefully and shown on the data sheet or on the sheet presenting the stress-strain

plot.


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Chapter 5

RESULTS AND DISCUSSIONS


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5.1 Preliminary observations and readings

5.1.1 Properties of black cotton soil

The engineering properties of soil are investigated as follows:

Liquid limit: 60.33%

Plastic limit: 21.5%

Plasticity index: 38.83%

Shrinkage limit: 13.66%

Differential swell: 70%

Optimum moisture content:26.4%

Maximum dry density: 1.33 gm/cc

Unconfined compressive strength: 30KN

5.1.2 Unconfined compressive strength tests results of different proportions

sr.no. proportion 7 day strength 14 day strength 21 day strength

1 4:10:100 63.26674 80.75306 79.10641

2 4:20:100 72.43254 45.99188 56.36429

3 4:30:100 67.97688 51.76302 104.6748

4 6:10:100 64.94172 127.2587 134.8742

5 6:20:100 91.38305 104.0796 104.0796

6 6:30:100 74.17492 81.52757 142.4454

7 8:10:100 99.61802 24.2101 123.7935

8 8:20:100 154.3113 123.8668 115.0261

9 8:30:100 88.99083 75.49722 191.4123


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5.1.3 Effect on strength when fly ash is varied keeping lime constant


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5.1.4 Effect on strength when lime is varied keeping fly ash constant


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5.1.5 Effect of curing time on the strength of the sub grade


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5.1.6 Discussions about the preliminary reading

The graphs of different combinations with different curing times have been drawn

and analyzed keeping two parameters constant.

The 5.1.3 graphs show variation in strength with variation with fly ash keeping

lime constant. From the graph, we come to know that the graphs are increasing

with the increase in fly ash. Thus, 30 % fly ash gives us the maximum strength.

However, we cannot understand whether the 30% is optimum proportion or not.

Hence we need to take tests with increasing the percentage of fly ash.

The 5.1.3 graphs show variation in strength with variation with lime keeping fly

ash constant. From the graph, we come to know that the graphs are increasing

with the increase in lime. Thus, 8 % lime gives us the maximum strength.

However, we cannot understand whether the 8% is optimum proportion or not.

Hence we need to take tests with increasing the percentage of lime.

The 5.1.3 graphs show variation in strength with variation with curing time. From

the graph, we observe that the better and reliable readings can be observed at the

curing time of 21 days. Hence, the final readings are taken for the curing time of

21 days.


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5.2 Final Observation and readings

Table 1 : unconfined compressive strength of black cotton soil taken after 21 day curing

Sr .no. lime fly ash 21 day compressive strength

1 4 10 79.10

2 4 20 56.36

3 4 30 104.67

4 4 40 43.4

5 4 50 22.28

6 4 60 21.06

7 6 10 134.87

8 6 20 104.07

9 6 30 142.44

10 6 40 38.3

11 6 50 15.24

12 6 60 21.08

13 8 10 123.79

14 8 20 115.02

15 8 30 191.41

16 8 40 62.90

17 8 50 38.75

18 8 60 64.19

19 10 10 100

20 10 20 105

21 10 30 112.51

22 10 40 111.06

23 10 50 100

24 10 60 50.34

25 12 10 140.4

26 12 20 160.3

27 12 30 195.66

28 12 40 190.2

29 12 50 117.4

30 12 60 100.56

31 14 10 120.7

32 14 20 140.64

33 14 30 180.24

34 14 40 179.19

35 14 50 115.57

36 14 60 70.8


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5.2.1 Variation in compressive strength with variation in fly ash

(explained using bar chart)


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5.2.2 Variation in compressive strength with variation in lime (explained

using bar chart)


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5.2.3 Variation in compressive strength with variation in fly ash

(explained using line graphs)


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5.2.4 Variation in compressive strength with variation in lime (explained

using line graphs)


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Discussions about the final readings obtained:

The final observation and readings have been analysed using bar charts and line

graphs.

From the graphs, we come to know that the strength of BC soil increases with

increase in lime content and then decreases with increase in lime. Thus, the

strength V/S lime percentage increases first and then drops down showing us the

optimum proportion of lime as 8%.

From the graphs, we come to know that the strength of BC soil increases with

increase in fly ash content and then decreases with increase in fly ash. Thus, the

strength V/S lime percentage increases first and then drops down showing us the

optimum proportion of lime as 8%.

Thus, we come to know that the optimum proportion for black cotton soil of

sangli is 12% lime and 30% fly ash.


GEC BHARATPUR

Properties of black cotton soil with12% lime and 30% fly ash

Liquid limit: 42%

Plastic limit: 27.14%

Plasticity index: 14.86%

Shrinkage limit: 19.01%

Clay: 9 %

Differential swell: 25%

Optimum moisture content: 30%

Maximum dry density: 1.3 gm/cc

Unconfined compressive strength: 195 KN


GEC BHARATPUR

Comparison between black cotton soil with no stabilizer and black cotton soil added

with 12% lime and 30% fly ash

Index properties Black cotton soil

with no stabilizer

Black cotton soil with

12 % remarks

Liquid limit 60.33 % 42.00 Liquid limit has

decreased

Plastic limit 21.50 27.14 Plastic limit has

increased

Plasticity index 38.83 14.86 Plasticity index has

reduced

Shrinkage limit 13.66 19.01 Shrinkage limit has

increased

Differential swell 70% 25%

Swelling has

decresed

considerably

Optimum moisture

content 26.4% 30% OMC has increased

Maximum dry density 1.33 gm/cc 1.3 gm/cc MDD has

decreased little.

Unconfined

compressive strength 30 KN 195 KN

Strength has

increased

considerably

Desired properties of soil have been achieved. Hence, stabilization method

and proportion of lime, fly ash and soil is correct.


GEC BHARATPUR

Chapter 6

Application formula


GEC BHARATPUR

6.1 Explanation of the derivation of formula

Lime is used for increasing the strength of sub grade soil whereas fly ash is used to bring

economy in the process.

From our research, we come to know that the strength achieved per percentage of lime is

25 KN and the strength achieved per percentage of fly ash is 3 KN.

Thus, the one percent of lime is equivalent to 8.33 percent of fly ash.

Thus, the use of lime can be reduced by replacing the lime with equivalent percentage of

fly ash thereby maintaining the same strength.

However, Through our research, we come to know that the optimum percentage of fly ash

is 30 percent and maximum fly ash that can be used is 35 %.

Thus, we limit the value of QF in equation below to 35 %.

6.2 Step wise procedure for calculating the percentage of lime and fly

ash required for stabilization of any black cotton

Step 1 – find out the Ph of the black cotton soil

Step 2 – Use ASTM D 6276 to calculate the minimum lime required for stabilization of

BC soil

Step 3 – Use the following formula to calculate the percentage of lime to be added and

percentage of fly ash to be added

QL = Q0 - (C – M )

(C/Q0 )

QF = (Q – Q0 ) * 8.33

Where, QL = percentage of lime that will be used

Q0 = percentage of lime required as per ASTM D 6276

QF = percentage of fly ash required to replace lime

C = cost of using Q0 percentage of lime

M = available money or budget of stabilization


GEC BHARATPUR

Chapter 7

CONCLUSION & SCOPE


GEC BHARATPUR

7.1 Conclusion

Lime and fly ash are effective and efficient stabilizer. The strength of black cotton

soil can be increased by using fly ash and lime combination.

Through our research, we have come to know the optimum proportion of lime and

fly ash for the locally available BC soil in Sangli. The optimum proportion is 12%

lime and 30% fly ash.

Through the differential swell reading, we come to know that for the optimum

proportion the swelling is considerably reduced. Thus, fly ash and lime can

effective in both increasing strength as well as reducing swelling of BC soil.


GEC BHARATPUR

7.2 Future scope of the project

In the project, we have calculated the optimum proportion of lime and fly ash for

black cotton soil available in sangli district. However, there is need to generalize

the use of lime + fly ash combination on black cotton soils. The use of fly ash and

lime can be generalized for all black cotton soils if the clay percentage for

different lime + fly ash combinations can be found out. By knowing the effect of

different combinations on clay percentage of soil, we can find out the optimum

proportion for any black cotton soil with particular clay percentage.


GEC BHARATPUR

Chapter 8

REFERENCES


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8.1 books

Behaviour of saturated expansive soil and control methods vol 1. - Prof. Katti

Soil Mechanics and Foundation engineering – Dr. K.S.Arora

8.2 Technical research papers

Baban ram and Sunil kumar chaudhary, “ Cost effective and eco friendly

construction of rural roads- need of hour”, Indian highways, Nov 2010

S. Bhuvaneshwari , S. G. Robinson , S. R. Gandhi . “Stabilization of expansive

soils using fly ash”, fly ash utilization program, TIFAC, DST, new Delhi

Erdal Cocka (2001) “ Use of class c fly ashes for the stabilization of an expansive

soil”, Journal of geotechnical and geoenvironmental engineering, vol. 127, July,

pp. 568-573

Pandian, n.s.,krishna, k.c. leelavathamma b., (2002), effect of fly ash on the cbr

behavior of Soils , Indian geotechnical conference , Allahabad , vol.1,pp.183-186.

Phanikumar b.r., & radhey s.sharma(2004) “effect of fly ash on engg properties of

expansive Soil” journal of geotechnical and geoenvironmental engineering vol.

130, no 7,july, pp. 764-767.

O.o. amu, a.b. fajobi and b.o. oke. “effect of eggshell powder on the stabilizing

potential of lime on an expansive clay soil”. Research journal of agriculture and

biological sciences 1(1): 80-84, 2005 © 2005, insinet publication

Niroj MIshra, Sudhira Rath, Siddharth Sankar biswat, Girija Sankar Pujhari,” Use

of fly ash and other stabilizing agents for construction of cost effective roads in

sambhalpur district in Orissa, Indian Highways, July 2010.

A. Shrirama rao and G. Shridevi , “ Improving the performance of expansive soil

subgrades with lime – stabilized fly ash cushion, Indian highways , oct 2010

A.N. Ramakrishna and A.V. Pradeepkumar, “Effect of moisture content on

strength behavior of BC soil- Rice husk ash- lime mixes, Indian Highways, jan

2008.

N. K. Ameta, d.g. m. Purohit, a. S. Wayal .”Characteristics, problems and

remedies of expansive soils of rajasthan”, india.


GEC BHARATPUR

Udayashankar d. Hakari s. C. Puranik “evaluation of swell potential and

identification of expansive and problematic soils in civil engineering works by

newly developed matrices Based on index and grain size properties”

Hesham ahmed hussin ismaiel “treatment and improvement of the geotechnical

properties of different soft fine-grained soils using chemical stabilization”

stabilization of black cotton soil

Documents

fly ash

civil engineering of

engineering college

guidance of

project work

gec bharatpur page

lime mixture

optimum proportion of