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Proceedings of Indian Geotechnical ConferenceDecember 15-17, 2011, Kochi (Paper No.J-258)

STUDY OF RUT BEHAVIOUR OF COIR REINFORCED BLACK COTTON SOIL

USING WHEEL TRACKING APPARATUS

A. K. Raji, Assistant Professor, NSS College of Engineering - Palakkad, email: rajiudayakumar@gmail.com

R. Karthika, G. R. Amruthalekshmi, Anju K. Peter, M. Mohamed Sajeer, Under Graduate Students, NSS College of

Engineering - Palakkad, email: karthikar7@gmail.com

ABSTRACT: In flexible pavement construction, if a problematic or weak subgrade soil is encountered, then either

chemical stabilisation or replacement with a good soil is the general solution. Stabilisation with chemical agents like

cement or lime is neither economical nor eco-friendly. The application of fly ash and/or coir geotextile is investigated in

this study by conducting various laboratory tests, including compaction and California Bearing Ratio (CBR) tests. A field

simulation was carried out on selected subgrade systems using a Wheel Tracking Apparatus fabricated in the laboratory.

The rut depth and wheel repetitions obtained can be utilised for predicting the design life of unpaved roads in terms of

number of load repetitions.

INTRODUCTION

Pavement is a structure formed by natural or borrowed soil,

on which other granular layers such as sub-base, base,

asphaltic concrete and cement concrete are laid. The quality

and stability of subgrade are some of the major factors

responsible for adequate performance and service of the

road during its lifespan.

One of the main problems faced by the highway engineers

is the instability of subgrade[1]. Several research works are

being carried out all over the world to improve its

mechanical or engineering properties[2-11]. Among these

researches, major development is the reinforced soil.Reinforced soil is formed by association of frictional soil

and tension resistant element in the form of sheets, strips,

nets or mats of metal, synthetic or fibre reinforced plastic,

coir, jute, etc.

Though many published works are available on the study of

strength characteristics of stabilised soil, rut analysis is still

under research. This paper discusses the strength of

subgrade in terms of rutting behaviour of plain soil (i.e.

unreinforced) and to compare it with that of soil stabilised

with fly ash and coir geotextile using Wheel Tracking

Apparatus and thereby to frame a mechanistic design

methodology for pavements.

OBJECTIVES

Roads running on black cotton soils are known for bad

condition and unpredictable behaviour. Modification ofblack cotton soils by chemical admixtures is a common

method for stabilizing the swell-shrink tendency of

expansive soils[4,6,7]. Advantages of chemical stabilisation

are that they reduce the swell-shrink tendency of the

expansive soils and also render the soils less plastic.

Stabilisation of problematic black cotton soil with chemical

agents like cement or lime is neither economical nor

ecofriendly and increases carbon footprints. This work aims

at studying the rut behaviour of subgrade soil or unpaved

roads reinforced with coir geotextiles and also stabilised

with fly ash in place of ordinary Portland cement and

thereby to evolve a mechanistic design approach for the

pavements[12].

MATERIALS USEDThe materials used in the study are subgrade soil, fly ash,

ordinary Portland cement and coir geotextile.

Subgrade Soil: The subgrade soil selected was black cotton

soil from Menonpara region in Vadakarapathy Panchayat,

Palakkad, where the pavement distress was found to bevery high. The engineering properties of the soil were

studied in detail and the soil was classified[13,16]. The

properties of the soil are summarized in Table 1. The soil

was found to have a very low CBR value of 5 per cent and

hence proved to be poor in action as subgrade.

Table 1 Physical properties of the Subgrade soil selected

Property Subgrade soil

Specific gravity 2.59

Gradation size >4.75mm (%)

4.75mm-0.075mm (%)

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A. K. Raji, R. Karthika, G. R. Amruthalekshmi, Anju K. Peter & M. Mohamed Sajeer

Fly Ash: The fly ash procured from Neyveli Lignite

Corporation, Neyveli was selected for stabilisation of the

subgrade and its properties are listed in Table 2.

Table 2 Properties of Fly ash

Properties Value

Specific Gravity 2.9Gradation size (%) >4.75mm

4.75mm-0.075mm

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Study of rut behaviour of coir reinforced black cotton soil using wheel tracking apparatus

heavily, swell, become soft, loose strength, be susceptible

to compression and with a tendency to heave during wet

condition. They are expansive and can undergo volumetric

changes leading to pavement distortion. Also it is

susceptible to shrinkage characterized by extreme hardness

and cracks when dry. When tested for rut behaviour using

Wheel Tracking Apparatus, the soil underwent a rut depth

of about 12mm at 1300 load repetitions indicating the poor

strength of the soil.

The properties like CBR and rut depth of the black cotton

soil were found to vary with the introduction of marginal

materials such as fly ash, cement and geotextile. The results

obtained from the experiments conducted are presented in

Table 5 and are illustrated in Figures 1 and 2.

Table 5 Variation in properties with introduction ofmarginal materials

CBR value Average rut at 1000

no. of repetitions

Sl

No.

Value %increase

Value %decrease

1. Soil 5 - 8.9 -

2. Soil +

Geotextile 12 140 7.4 17

3. Soil + 5%

Flyash +

2.5%

Cement

20 300 6.2 30

4. Soil + 5%

Flyash +

2.5%

Cement +

Geotextile

28 460 5.1 43

Fly ash as a Stabilizing Agent

In order to find out the optimum fly ash content giving themaximum strength, the fly ash content was varied and the

different properties were studied. At about 5 per cent fly

ash content, the CBR was found to increase by 73 per cent.

Also, with the addition of 2.5 per cent cement along with 5

per cent fly ash, the CBR was further increased and the

following observations were made.

x The CBR value gets increased to 20 per cent, i.e. an

increase of about 300 per cent.

x A dry density of 19.2kN/m3 is obtained at 12 per centwater content.

x The rut depth has decreased from 8.9mm to 6.2mm at

1000 load repetitions giving a per centage decrease of

30 per cent.

Geotextile as Reinforcement

The soil was stabilised with coir geotextile (H2M8). For

performing the CBR test, the geotextile was placed at a mid

depth of the mould while compacting. In the field

simulation test for the measurement of rut depth, a layer of

Fig. 1 Load Vs penetration for different soil systems

Fig. 2 Comparison of Rut depth for different soil systems

geotextile was provided at a depth of 15cm and above that

the soil was compacted in layers to form the subgrade. Thefollowing inferences were drawn from the experiments

conducted on soil reinforced with geotextile:

x CBR of soil reinforced with geotextile is increased to

12 per cent, i.e. about 140 per cent increase.

x CBR of soil stabilised with 5 per cent fly ash and 2.5

per cent cement and reinforced with geotextile is

found to be excellent and comes to 28 per cent, i.e. an

increase of 460 per cent.

x Maximum rut depth in soil reinforced with geotextile

at 1000 number of repetitions is 10.6mm.

x Maximum rut depth in soil stabilised with 5 per centfly ash and 2.5 per cent cement and reinforced with

geotextile at 1000 number of repetitions is 5.72mm.

Estimation of Design Load Repetitions

In the light of the above discussion, a design approach to

estimate the wheel load repetitions has been suggested in

the study. Thus, from the plot, rut depth (in mm) Vs

number of load repetitions, equations correlating rut depth

(Y) and number of load repetitions (X) were formulated.

Using the above equations, for a specified rut depth, the

number of load repetitions can be estimated from which the

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A. K. Raji, R. Karthika, G. R. Amruthalekshmi, Anju K. Peter & M. Mohamed Sajeer

design life of the pavement can be predicted. The details are

given in Table 6.

Table 6 Equations for Mechanistic Design approach

Soil combination Equation Coefficient of

Determination

(R

2

)Soil alone Y = -2x10-6X2 +

0.005X + 5.223

0.990

Soil + Geotextile Y = -1x10-6X2 +

0.004X + 4.127

0.988

Soil + 5% Flyash

+ 2.5% Cement

Y = 2x10-8X2 +

0.001X + 5.003

0.954

Soil + 5% Flyash

+ 2.5% Cement +

Geotextile

Y = -2x10-6X2

+0.002X + 3.900

0.989

Note: Y is the rut depth in mm and X is the number of wheelload repetitions.

CONCLUSIONSThe strength characteristics of the selected subgrade soil in

terms of CBR and rut depth were studied in detail through

various experiments. Measures were adopted to improve

the strength by the introduction of marginal materials. The

following conclusions were arrived at from the

experiments:

i. Wheel Tracking Apparatus can be effectively used for

studying the rut failure of pavements simulating the

field conditions.

ii. The results of rut analysis found to correlate with the

CBR values obtained.

iii. Stabilisation of black cotton soil with flyash and

cement increases its CBR by 300 per cent and

decreases the rut depth by 30 per cent.

iv. Reinforcing the soil with geotextile can improve the

strength characteristics of the soil. It can increase the

CBR by 140 per cent and decrease the rut depth by 17

per cent.

v. The highest performing subgrade was obtained with

the application of flyash, cement and coir geotextile.

vi. Equations for mechanistic design approach have been

formulated by which the design life of pavement can

be estimated.

ACKNOWLEDGEMENTS

The financial assistance rendered by the Kerala State

Council for Science Technology and Environment(KSCSTE) for the study is gratefully acknowledged.

REFERENCES

1. Bhavanna Rao, Poor condition of Roads on blackcotton soils and Steps to improve, NBMCW,September 2007.

2. Dutta N. and Sarda V. K., CBR Behaviour of WastePlastic Strip-Reinforced Stone Dust/Fly Ash OverlyingSaturated Clay, Turkish J. Eng. Env. Sci., 31 (2007),171 182.

3. Guide for Designing Subgrade EnhancementGeotextiles.

4. Katti R. K., Dinesh R. Katti, Katti A. R.,Behaviour ofSaturated Expansive Soil and Control Methods,Revised and Enlarged edition, A. A. Balkema.

5. Kulkarni A. W., Shah M. H., Decate M. N. and

Adhikari A., Strengthening of Road in Black CottonSoil Region and Improvement of Overlay against

Reflective and Fatigue Cracking using Geosynthetics,Geosynthetics Asia97, 26-29 November, Banglore,

India.

6. Osinubi K. J., Oyelakin M. A. and Eberemu A. O.,

Improvement of Black Cotton Soil with OrdinaryPortland Cement - Locust Bean Waste Ash Blend,EJGE Vol. 16 [2011], Bund. F.

7. Rama Rao M and Sridevi G, Effect of Lime StabilisedFlyash Layer On CBR Values Of Black Cotton Soils,IGC-2005, 17-19 December 2005, Ahmedabad,

INDIA.

8. Ramesh H. N., Manoj Krishna K. V. and Mamatha H.

V., Compaction and strength behavior of lime-coirfiber treated Black Cotton soil, Geomechanics andEngineering, Vol. 2, No. 1 (2010) 19-28.

9. Sahu B. K., Improvement in California Bearing Ratioof various soils in Botswana by Flyash, 2001International Ash Utilisation Symbosium, Center for

Applied Energy Research, University of Kentucky.

10. Subaida E.A., Chandrakaran S. and Sankar N.,

Laboratory Performance of Unpaved Roads

Reinforced with Woven Coir Geotextiles, Geotextilesand Geomembranes, Volume 27, Issue 3, June 2009,

Pages 204-210.

11. Vinod P. and Minu Michael, California Bearing Ratioof Coir Geotextile Reinforced Subgrade, 10th NationalConference on Technological Trends (NCTT09) 6-7

Nov 2009.

12. Partha Chakraborty and Animesh Das, Principles ofTransportation Engineering, Prentice Hall of IndiaPrivate Ltd, New Delhi 2003.

13. Arora.K.R., Soil Mechanics and FoundationEngineering, Standard Publishers Distributers, Delhi.

14. http://www.keralacoir.co.in/moregeo_frm.htm

15. Kadiyali.L.R., Principles of Highway Engineering,Khanna Publishers, New Delhi.

16. Khanna S.K. and Justo, CEG, Highway Engineering,NemChand and bros.

17. IRC 37-2001, Guidelines for the Design of FlexiblePavements, Indian Roads Congress, New Delhi.

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