metalled road on canal service bank

METALLED ROAD ON CANAL SERVICE BANK

1. General Description 1.1 The service road on the left bank of Haidergarh and Jaunpur branches

are proposed to provided with a metalled road as one of the redesign initiative under the rehabilitation and modernization of the irrigation systems of the project area. The proposed road is classified as village road and the design procedure and construction methodologies discussed in the “Rural Road Manual” of the Indian Road Congress as published in their special publication no. IRC:SP:20:2002 shall be followed.

1.2 The planning and alignment aspects generally considered for a village

road are not of significance in case of canal bank road as this construction is guided according to the necessities of the canal operation and management communication network and the alignment is decided according to the existing alignment of the canal. The primary consideration is the movement of inspecting and regulation personnel manning the system. This is not only necessary from the point of view of requirements of modernized operation and management system, but also the transfer of management to the Water Users’ Association’s. No doubt habitations have been provided priority for an all weather road connectivity solely based on its population size, in the present case however, this will be an additional infrastructural facility for the connected population along the branch canal and shall provide easy access to large markets for evacuation of produce, particularly the fast decaying vegetables, flowers and fish etc.

1.3 Geometric design standards for the village roads is recommended in

the village road manual. In the present case, the classification of the road or consideration of terrain etc are not relevant. However, the guidelines regarding the design speed, cross sectional elements as recommended in the Rural Road Manual and as far as they are applicable to the present case and which are detailed below, need to be considered.

2. Design Criteria 2.1 Design Speed

Design speed is a basic criterion for determining all geometric features of horizontal and vertical alignments. The design speeds for the rural roads should be taken as given in Table 1 below.

Table 1 : Design Speed

Road Classification

Design Speed (Km/h)Plain Terrain Rolling

TerrainMountainous Terrain

Steep Terrain

Ruling Min. Ruling Min. Ruling Min. Ruling Min.Rural Roads (ODR & VR)

50 40 40 35 25 20 25 20

Normally ruling design speed should be the guiding criterion for the purpose of geometric design. Minimum design speed may, however, be adopted where site condition and cost does not permit a design based on “Ruling Design Speed”.

2.2 Cross Sectional Elements 2.2.1 Road Land Width

Road land width (also termed the right-of-way) is the width of land acquired for road purposes. The desirable land width for rural roads in different terrain is given in Table 2 below.

Table 2 : Recommended Road Land Width

Road Classification

Design Speed (Km/h)Plain and Rolling Terrain Mountainous and Steep TerrainOpen Area Built-up Area Open Area Built-up AreaNormal Range Normal Range Normal Exceptional Normal Exceptional

Rural Roads (ODR & VR), (m)

15 15-25 15 15.20 12 12 12 9

Note : In the present case the total bank width available is the limiting land width 2.2.2 Building and Control Lines

In order to prevent overcrowding and preserve suffiecient space for future road development, it is advisable to lay down restrictions on building activity along the rural roads. Recommended standards for

building lines and control lines are given in Table 3 below. This specific provision is not applicable in the design of metalled road on canal banks.

Table 3 : Recommended Standards for Building & Control Lines

Road Classification

Plain and Rolling Terrain Mountainous and Steep Terrain

Open Area Built-up Area Open Area Built-up AreaOverall width between bidg. lines

Overall width between control lines

Distance between bidg. Line & road boundary (set-back)

Distance between bidg. Line & road boundary (set-back)

Rural Roads (ODR & VR), (m)

25/30 35 3-5 3-5 3-5

2.2.3 Roadway Width

Roadway width inclusive of parapet, side drains for rural roads for different terrain shall be as given in Table 4.

Table 4 : Recommended Roadway Width

Terrain Classification Roadway Width (m)Plain and Rolling 7.5Mountainous and Steep 6.0

Notes : (i) For rural roads, where the traffic intensity is less than 100 motor vehicles per day,

and where the traffic is not likely to increase due to situation like dead end, low habitation and difficult terrain conditions the roadway width may be reduced to 6.0m in case of plain and rolling terrain.

(ii) The roadway width given in the Table 4 for mountainous and steep terrain is inclusive of parapet.

(iii) The roadway width for Rural Roads is on the basis of a single lane carriageway of 3.75m.

(iv) On horizontal curves the roadway width should be increased corresponding to the extra width of carriageway for curvature.

(v) On roads subjected to heavy snowfall and landslides, where regular snow or debris clearance is done over long period to keep the road open to traffic, roadway width may be increased by 1.5m.

2.2.4 Carriageway Width

The standard width of carriageway for both plain and rolling as well as mountainous and steep terrain shall be as given inTable 5. Typical cross sections of rural roads are given in Figure 2.2 and 2.3.

Table 5 : Recommended Carriageway Width

Road Classification Carriageway Width (m)Rural Roads 3.75

Note : For rural roads, the carriageway width may be restricted to 3.0m, where the traffic intensity is less than 100 motorized vehicles per day, and where the traffic is not likely to increase due to situation, like, dead end, low habilitation and difficult terrain conditions. 2.2.5 Shoulder Width

The width of shoulder for rural roads in different terrain can be directly obtained using Table 4 and 5. Shoulder width will be one half the difference between the roadway width and carriageway width.

2.2.6 Side Slope

Side slope for rural road where embankment height is less than 3.0m is given in Table 6 below:

Table 6 : Side Slope for Rural Roads

Condition Slope (H:V)Embankment in silty/sandy/gravelly soil 2:1Embankment in clay or clayey silt or inundated condition 2 ½ :1 to 3:1Cutting in silty/sand/gravelly soil 1:1 to ½:1Cutting in disintegrated rock or conglomerate ½:1 to ¼:1Cutting in soft rock like shale ¼:1 to 1/8:1Cutting in medium rock like sandstone, phyllite 1/12:1 to 1/16:1Cutting in hard rock like quartzite, granite Near vertical

2.3 Camber

The camber on straight section of road should be as recommended in Table 7.

Table 7 : Camber for Different Surface Types

Surface Type Camber (Percent)

Low Rainfall (Annual Rainfall < 1000mm)

High Rainfall (Annual Rainfall > 1000mm)

Earth road 4.0 5.0WBM and gravel road 3.5 4.0Thin bituminous pavement 3.0 3.5Rigid pavement 2.0 2.5

At super-elevated road sections, the shoulder should normally have the slope of same magnitude and direction as the pavement slope subject to the minimum cross fall allowable for shoulder. The camber for earth shoulder should be at least 0.5 percent more than that for the pavement subject to the minimum of 4 percent. However,1 percent more slope than the camber for pavement is desirable.

2.4 Superelevation

Superelevation to be provided on curve is calculated from the following formula:

Where e = Superelevation in metre per metre V = Design speed in km/hr R = Radius of the curve in metres

Superelevation obtained from the above expression should, however, be kept limited to the following values :

Plain and rolling terrain 7 percent Snow bound area 7 percent Hilly area but not snow bound 10 percent

3. Design Assumptions As described in Para 2.1 above, design speed of moving vehicle is a basic criteria for determining all geometric feature for alignment. The design speed (km/h) for rural road in plain terrain is recommended as 40 km/h minimum and 50 km/h ruling. As the expected vehicular traffic will mostly be inspection vehicles, tractors and some heavy agricultural vehicle (only on a few occasions), it is proposed to adopt the minimum design speed for purpose of geometric design. Roadway width in this case is limited to the width of the top of the bank and is taken as such. The other details are as follows-

1. Carriageway widths – 3.75 m (Table 5).2. Shoulder width – 0.5 m on Daula side and 1.5 m on berm side.3. Brickedging – 7.0 cm on either side of the carriageway.4. Side slope (outer bank) – 1.5:1 or 2:1 as per site conditions.

5. Camber 3% from outer road edge to canal side- as the proposed road is not likely to have a heavy concentration of fast moving traffic; super elevation in the curved reaches is not proposed. This will also take care for the uniform camber from canal outside to canal inside.

6. Motorized traffic per day – 157. Traffic growth rate – 6%8. Designed life – 10 years9. Design CBR– 5.0%

4. Pavement Design 4.1 Introduction

The road formation structural disposition for the purposes of construction of village roads is generally divided into four major component viz land earth work, pavement and cross drainage works. In the present case where village road construction is proposed on an existing canal bank, the components of land, earth work and cross drainage works are not of any material significance. The CVR value requirement for deciding the pavement thickness is however a very crucial parameter from the considerations of designs features. The following factors govern the selection of type of pavement:

(a) Initial (construction) cost(b) Availability of good materials locally(c) Cost of maintenance or rehabilitation during service(d) Technology of construction required and its availability

The various alternatives available for the type of pavement are: (a) flexible pavement, (b) cement concrete pavement, (c) composite pavement with semi-rigid base with suitable bituminous surfacing, (d) semi-rigid base with surfacing of inter connected concrete paving blocks, and (e) roller compacted concrete. Flexible pavement is the most common option for normal traffic conditions. Concrete pavement is being provided now for high density traffic corridors and expressways.

In view of the initial cost advantage in the present case of construction of rural road on canal bank, the flexible pavement option will be the appropriate choice. Other options like roller compacted concrete, block pavements and composite pavements may be cost affective in some rural road projects where ground conditions and material availability

restrict the use of flexible pavement. The pavement choice is further guided by following factors.

(i) Rainfall and temperature(ii) Type and strength of soil along the alignment(iii) Availability of good aggregates(iv) Availability of industrial wastes (like, fly ash, slag, etc.) in the

proximity

Appropriate choice based on the above guidelines and with a view to economize the over all cost of the project, without in any way compromising the quality aspects can be exercised by the engineer. While it may appear that rural roads will not have traffic intensity or axle loads as compared to roads of higher category, even the small number of commercial vehicles (or tractor, trolley), with heavy axle loads or iron-tyred animal drawn cart may cause heavy damage to an under designed pavement. The suitability and sufficiency of pavement design need therefore be given due importance. Any design using conventional, marginal or waste material must follow standard procedure based on material property, traffic and design life. There are many associated factors like rainfall, ground water table, etc. which are also to be taken into account for evolving durable pavement design. In all designs economy in the initial cost as well as in life cycle cost are crucial and very important. These aspects assume extra emphasis in case of rural roads.

4.2 Design Parameters 4.2.1 General :

According to Rural Road Manual of IRC, the principal criterion for determining the thickness of a flexible pavement with a thin bituminous surfacing is the vertical compressive strain on top of the sub grade imposed by a standard axle load of magnitude 8.17kN (8170kg). The design curves as per IRC:37 are valid for the design traffic from 0.1 million standard axles (msa) to 2 msa. This has been demonstrated by analytical evaluation of performance of district and village roads on the basis of the vertical sub grade strain criterion. As the village road constructions are generally done through local agencies, the design charts have to be much simpler from the view point of convenience in use. Design curves are also prepared for sub-grade CBR upto 20 percent. The minimum recommended pavement thickness is 150mm even when design chart gives lower values. In the case of semi rigid pavements, however, tensile stress is taken as the

design criteria to prevent fracture of the concrete layer within the design period. Vertical sub-grade strain is the critical criteria to limit rut depth due to traffic loading in case of concrete block pavements.

4.2.2 Traffic :

As per the general guidelines suggested in the Rural Road Manual, for the purpose of structural design, only the number of commercial vehicles of laden weight 3 tonnes or more should be considered. To obtain a realistic estimate of design traffic, due consideration should be given to the existing traffic and its rate of growth. If adequate data is not available, an average value of 6 percent may be adopted for traffic growth rate.

4.2.3 Design Life :

It is considered appropriate that roads in rural areas should be designed for a design life of 10 years. The thin bituminous surfacing that is commonly provided on the low volume roads has a life of about 5 years. The traffic to be carried during the design life of the road is the main consideration for design traffic.

4.2.4 Computation of Design Traffic :

In case of rural roads the commercial vehicles will be trucks (small and big), buses and tractor-trolley. The traffic for the design life is computed as :

Where

A = Number of commercial vehicles per day for design P = Number of commercial vehicles per day at last count r = Annual growth rate of commercial traffic

n = Number of years between the last count and the year of completion of construction

x = Design life in years

Since the width of rural roads will be single lane, design traffic should be based on total number of commercial vehicles per day in both directions. Bullock carts with iron rims are still in use in different parts of the country and the total eight including the pay load of a bullock cart may range from 1.0 tonne to 1.5 tonnes. Though the designed pavement as a whole will be safe from shear failure, the iron rims damage the top layer of the pavement because of high concentration

of stress. Thus the wearing course must be made up of good quality aggregates with aggregate impact value not exceeding 30 percent to reduce degradation of the aggregates by crushing.

4.2.5 Pavements Components :

As per the IRC “Rural Road Manual” the various pavement components are as described herein below:

Sub Grade – The sub-grade, in case of a rural roads is the top 30cm of the cutting or embankment at the formation level. In the present case, the formation being the canal bank, the criteria has accordingly to be applied with reference to the existing embankment. The embankment should be well compacted to utilize its inherent strength and prevent deformation due to further compaction by traffic. A minimum of 100 percent of Standard Proctor compaction should be attained in the top 30cm of the sub-grade. For clayey soil, the minimum compaction for sub-grade should be 95 percent of Standard Proctor compaction and the compaction should be done at moisture content 2 percent in excess of the optimum value. For embankment, the soil below 30cm of sub-grade shall be compacted to minimum 97 percent of Standard Proctor compaction [IS : 2720 (Part 7)-1980]. For pavement design, the sub-grade strength should be determined in terms of CBR at the most critical moisture conditions likely to occur. The CBR test should be conducted on remolded samples prepared at optimum moisture content and dry density corresponding to Standard Proctor compaction [(IS:2720 (Part 7)-1980] and soaked in water for four days prior to testing. If the annual rainfall is of the order of 500mm or less and the water table is too deep, soaking for four days may not be necessary.

One or two CRB tests should be done per kilometre depending on the variation of soil type. If there is no variation in soil type, mean CBR value should be adopted for the design of pavements. In case of existing roads requiring strengthening, the soil should be moulded at the existing moisture content and field density, and soaked for four days prior to testing for CBR.

Where the CBR of the subgrade is less than 2 percent a capping layer of 100mm thickness of material with a minimum CBR of 10 percent is to be provided in addition to the sub-base required for CBR of 2 percent. If the sub-grade CBR is more than 15 percent, there is no need to provided a sub-base. WBM base can be laid directly over the sub-grade after providing a drainage layer (inverted choke).

Sub-Base : Sub base is a layer of selected material placed on the sub-grade compacted to 98 percent of the IS heavy compaction. Generally it consists of locally available, relatively low strength inexpensive material. The principal function of the sub-base is to distribute the stresses over a wide area of the sub-grade imposed by traffic and to ensure that no sub-grade material intrude into the base course and vise versa. There are a large number of locally available aggregates and industrial waste material that can be utilized for sub-bases of pavements.

The sub-base material should have minimum soaked CBR of 15 percent. Material component of sub-base passing 425 micron IS sieve when tested in accordance with [IS:2720(Part 5)-1985] should have liquid limit and plasticity index not more than 25 and 6 respectively. These requirements should be enforced to achieve desired quality.

When the sub-grade is silty or clayey soil and the annual rainfall of the area is more than 1000mm, a drainage layer of 100mm over the entire formation width should be provided conforming to the prescribed gradation. This layer will form a part of the designed thickness of sub-base.

Base : The base course materials should be of good quality so as to

withstand high stress concentration which develop immediately under the wearing surface. Since bituminous surfacing consists only of a thin wearing course, the upper surface of the base must be sufficiently smooth and true to profile to provide a good riding surface. The different types of base course which are commonly used are:

(a) Water bound macadam (WBM)(b) Crusher-run macadam(c) Dry lean concrete(d) Soft aggregate base course(e) Lime fly ash concrete

Thickness deduced from the design charts are appropriate to pavements with unbound granular bases which comprise of conventional WBM or any other equivalent granular construction. For cement treated or stabilized materials, thorough laboratory investigations are necessary and the pavement design can be done using analytical method. In some situations where good quality aggregates are not available, cement treated low grade aggregates or soils may also be used. Appropriate agency may be approached for laboratory investigations and design.

It is recommended that normally no material with CBR value less than 100 percent should be used in base courses. Since base course will be affected by water, their strength should be determined in soaked condition. Where a substantial part of the base material consists of particles larger than 20mm size, the CBR test will not be applicable and their strength will have to be estimated from experience. WBM of adequate thickness over a properly designed sub-base will be assumed to satisfy the CBR requirements of 100 percent. The design of base courses of different types are given in subsequent sections.

Pavement Surface : Pavement can be with a sealed or unsealed

surface. The unsealed surface means a granular surface where percolation of water into the pavement layers is possible, whereas in sealed surface it is prevented by appropriate surfacing layer. Details of the design or choice of surfacing are given below:

A gravel road or WBM layer can serve adequately as a surfacing depending on traffic volume. However, it is to be clearly understood that granular materials (like, soil-gravel mixture) will be lost gradually by traffic action and thickness will be reduced. Therefore, for gravel roads extra thickness should be provided. Further, for similar reasons, only WBM Grade-III should be used as a surfacing course for an unsealed WBM road. Other granular surfacing, like, Moorum, Kankar etc. will have to be bladed as and when required to provide smooth riding surface.

4.2.6 Design of Flexible Pavement Pavement Thickness : The thickness of pavement is designed on

the basis of projected number of commercial vehicles for the design life using the current commercial vehicles per day and its growth rate. Further, it requires the sub-grade strength value in terms of CBR. It is expected that rural road will not have more than 450 CVPD in any case. The design chart given in Figure-1 may be referred to obtain the total pavement crust thickness (granular crust thickness) required over the sub-grade for the design life of the pavement. Based on the strength of granular materials that are used, the total design thickness is divided into base and sub-base thicknesses. However, any other higher type of bituminous layer can be part of the designed thickness, with the exception of thin bituminous surfacing (PMC, MSS, etc). In case of rural roads, with low volume of traffic, structural layer of bituminous mix need not be provided, generally except in very special cases where the traffic volume is so high that the design suggests it.

For the convenience of engineers the whole range of traffic and CBR that exist for rural roads in various States of the country have been considered and flexible pavement thickness catalogues are given in Figures-2, 3 and 4 for ready reference.

A B C D

A B C D

A B C D Sub-base Course Base

Course Surfacing

Fig 2 : Thickness of crust required for different traffic

A B C D

A B C D

A B C D

Sub-base Course Base Course Surfacing


A B C D A B C D

A B C D Sub-base Course Base Course Surfacing


The bituminous wearing course will generally consist of premix carpet with seal coat or two coat surface dressing laid over WBM base course or other type of bases. Bituminous wearing course must be made up of good quality aggregates with aggregate impact value not exceeding 30 percent in order to reduce degradation of the aggregates by crushing. Use of bituminous emulsion for such work may give good surfacing because of processing of material at ambient temperature. Maintaining the right mixing temperature of the hot mix is not easy when the dampness of aggregates stacked at the sites varies. Based on the total motorized traffic and rainfall, an appropriate surface can be chosen fromTable 8.

Table 8 : Guidelines on Surfacing for Rural Road

Annual Rainfall

(mm)1500+

Thin Bituminous Surfacing

(2-Coat Surface Dressing)

Bituminous Surfacing(Premix Carpet+Seal

Coat.)

Bituminous Surfacing(Premix Carpet+Seal

Coat)

1000-1500

Single CoatSurface Dressing


(2-Coat S.D.)

Bituminous Surfacing(PMC + Seal Coat)

500-1000

Unsealed Surface(Gravel Road)

Single CoatSurface Dressing


(2-Coat S.D.)

0-500Unsealed Surface

(Gravel Road)Unsealed Surface

(Gravel Road)Thin Bituminous

Surfacing(2-Coat S.D.)

0-50 50-150 150+

Motorised Traffic (Except 2 –Wheeler) Per Day

Note : S.D. = Surface Dressing PMC = Premix Carpet

metalled road on canal service bank

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