Transportation Geotechnics 2 (2015) 20–29

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Transportation Geotechnics

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Evaluation of lateritic soil stabilized with Arecanut coirfor low volume pavements

http://dx.doi.org/10.1016/j.trgeo.2014.09.0012214-3912/� 2014 Elsevier Ltd. All rights reserved.

⇑ Corresponding author at: Department of Civil Engineering, NationalInstitute of Technology Karnataka, Surathkal, Srinivasnagar P.O., Manga-lore 575025, India.

E-mail addresses: lekhabm@gmail.com (B.M. Lekha), gouthamsarang@gmail.com (S. Goutham), aurshankar@gmail.com (A.U.R. Shankar).

B.M. Lekha ⇑, S. Goutham, A.U.R. ShankarDepartment of Civil Engineering, National Institute of Technology Karnataka, Surathkal, India

a r t i c l e i n f o

Article history:Received 7 April 2014Revised 1 September 2014Accepted 5 September 2014Available online 17 September 2014

Keywords:Soil–cement–Arecanut coirUCSCBRFatigue lifeDurabilityKENPAVE

a b s t r a c t

Soil stabilization is a common method used by engineers and designers to enhance theproperties of soil with different stabilizers. From ancient times, usage of natural fiber in soilas reinforcement is an effective technology adopted. This paper presents the effect ofincluding randomly spaced Arecanut coir to the soil mix. The engineering properties andbearing capacity of a soil get enhanced by stabilizing it with Arecanut coir and a bindingmaterial (cement). The information available on experiments and research on the behaviorof soil cement mixtures were collected and a few studies conducted on fiber reinforcementwere referred. The current study mainly focuses on the durability test and physical evalu-ation of soil cement mixtures reinforced with Arecanut coir. Coir content was varied from0.2% to 1% with an increment of 0.2%. For further improvement, a uniform dosage of 3%cement was added to soil. Laboratory tests including the Unconfined Compressive Strength(UCS), California Bearing Ratio (CBR), durability and fatigue behavior, were conducted asper standards. The test results indicated that the improvement in characteristics of the soilcement coir mixtures were functions of coir dosage, soil type and curing days. Durabilitytest satisfied at 1% Arecanut coir with 3% cement. The stress–strain values were deter-mined and damage analysis was conducted for the higher dosage of Arecanut coir usingKENPAVE software. From the results it is observed that, the Arecanut coir reinforcedcement soil mix can be used for low volume roads (traffic 61 million standard axles)and few design cases have been discussed.

� 2014 Elsevier Ltd. All rights reserved.

Introduction

Subgrade is a structure formed by natural or borrowedsoil, on which other granular layers of pavement such assub-base, base and surface courses are laid. The qualityand stability of subgrade is a major factor responsible forthe adequate performance and service of any road duringits life span. Lateritic soils have been found in the coastal

region, along the Konkan belt of India. High rainfall,temperature and humidity with alternative wet and dryperiod, which are ideal conditions for laterization, makesnearly 40% of the soils in the area laterites. Its color rangesfrom red to yellowish red and depth from 30 to 150 cm.The laterites have been mostly originated from igneousrocks and are well drained residues with the presence ofexcessive Iron and Aluminum.

India is considered as the largest Arecanut producingcountry in the world. The total area under cultivation is264,000 hectares and the annual production is 313,000metric tonnes, with the states Karnataka and Keralaaccounting for nearly 72% of total production. Among allthe natural fiber-reinforcing materials, Arecanut fibre

B.M. Lekha et al. / Transportation Geotechnics 2 (2015) 20–29 21

appears to be a promising material because it is inexpen-sive, abundantly available and the crop is very high poten-tial perennial. The husk of the Arecanut is a hard fibrousportion covering the endosperm. It constitutes 30–45% ofthe total volume of the fruit. Areca husk fibers are predom-inantly composed of hemicelluloses.

The concept of soil reinforcement was first developed byVidal (1996). It was established that the introduction ofreinforcement elements in a soil mass increases the shearresistance of the soil matrix. Lekha and Sreedevi (2005)studied on coir fiber for stabilization of weak subgrade soils,which included treating the weak soil with coir fibre at dif-ferent quantities and studying the changes in OptimumMoisture Content (OMC), Maximum Dry Density (MDD)and California Bearing Ratio (CBR) values. The OMC wasfound to be increased with the increase in the percentageof coir fibre content and correspondingly, MDD decreased.Tang et al. (2007) investigated the effects of discrete shortpolypropylene fiber (PP-fiber) on the strength and mechan-ical behavior of uncemented and cemented clayey soil. Thetest results indicated that the inclusion of fiber reinforce-ment within uncemented and cemented soil causedincrease in the Unconfined Compressive Strength (UCS),shear strength and axial strain at failure, decrease in thestiffness and the loss of post-peak strength, and change inthe behavior of cemented soils from brittle to more ductile.

Kumar and Singh (2008) tried different combinations ofpolypropylene fiber and fly ash on soil. It was observedthat the addition of fiber to soil satisfy all the geotechnicalproperties to meet the requirements of sub base layer.Bijayananda et al. (2011) conducted a series of laboratorysoaked and unsoaked CBR tests on randomly oriented fiberreinforced and unreinforced specimens of clayey soil, com-pacted at OMC and MDD. Coir fiber has been used as a rein-forcing material to investigate its beneficial use in ruralroad subgrade soil. From CBR test results, the engineeringperformance of coir fiber inclusion was examined. Theresults indicated that the inclusion of coir fiber enhancedthe CBR strength of the soil specimens significantly. Clayeysoils mixed with fibers showed remarkable increase in theCBR strength in comparison with the same soils withoutfiber inclusions. That is, randomly oriented discrete fiberreinforcements in clayey subgrade offered higher resis-tance to penetration than unreinforced one, under similarloading conditions. Shankar et al. (2012) studied on litho-margic clay stabilized with different percentages of sandand coir and improvement in almost all properties wasobserved. The CBR both in soaked and unsoaked condition,increased as the percentage of sand increased from 0 to 40and coir from 0 to 0.5. When the sand content increasedfrom 0 to 40%, the UCS values of blended soil for both lightand modified compaction densities increased up to a cer-tain limit, whereas, the increase of coir content from 0 to0.5% resulted in a continuous increase in UCS. Even thoughArecanut coir is a biodegradable material, according toRamaswamy and Aziz (1989) its strength and conditionbeyond a period of one year after placement should notbe of any concern as by that time the coir would havealready played a very important role in providing a self-sustaining subgrade for most types of soils. The loss ofstrength of the coir with time can be well compensated

by the gain in strength of the subgrade within the sametime frame.

Kar and Pradhan (2012) studied on soil stabilized withfly ash and fiber reinforced fly ash for low volume roads.Soaked CBR values for reinforced fly ash soil showed goodimprovement. A study by Sarbaz et al. (2014) on soil speci-mens reinforced with palm fibers and bitumen coated fibersshowed that palm fibers significantly increases the CBRstrength of the sand specimens. Amadi (2014) conducteda series of durability tests on black cotton soil with cementkiln dust and quarry fines, and the results observed forhigher dosage of these stabilizers satisfied the durabilitycriteria. Maheshwari et al. (2012) conducted a series oflaboratory tests on unreinforced and fiber reinforced blackcotton soil with different amount of fibers and there was asignificant increase in CBR value with the inclusion of fibers.As per Indian Road Congress (IRC) standard IRC 37-2001, theflexible pavement sections resting on fiber reinforced soilfor traffic volumes of 1–150 msa were designed and mod-eled using finite element software Plaxis 2D. Considerablereduction in deformation was obtained on the top of sub-grade due to reinforcing of subgrade soil using fibers.Lekha et al. (2013) studied on laterite soil using Zycosoilchemical, and analysis conducted in KENPAVE softwareshowed that Water Bound Macadam (WBM) can bereplaced with treated soil for low volume roads.

Many researchers have tried to investigate the field per-formance of soils stabilized with randomly added fibers(Grogan et al., 1994, Newman et al., 2008, Hufenusa et al.,2006 Santoni et al., 2001, Zhang et al., 2003). Santoni andWebster (2001) reported fiber stabilization as an effectivemethod for military airfield and road applications basedon the field test conducted on sandy soil stabilized withfibers. For mixing fibers with the sand uniformly, a self-pro-pelled rotary mixer was used. The sand fiber layer wasturned over with the front end loader and four passes wereprovided with the mixer to obtain a proper sand-fiber mixthroughout the layer. Tingle et al. (2002) also followed thismethodology for mixing fibers and sand in the field, andperformed full-scale field tests.

No study has been reported on the usage of Arecanutcoir fibre for stabilization of soil. Since Arecanut cropsare available abundantly in Dakshina Kannada District ofKarnataka, a laboratory study has been carried out to studythe properties of lateritic soil with this fibre and cement.The main objective of this study was to determine the con-tribution of Arecanut coir to the shear strength of lateriticsoil. A series of tests were carried out to investigate theeffect of coir content on the behavior of soil.

Materials and methods

Lateritic soil

Lateritic soil was procured from NITK Surathkal cam-pus, Dakshina Kannada District, India. The geotechnicalproperties like specific gravity, soil classification, consis-tency limits, compaction characteristics, UCS and CBR val-ues were conducted as per the relevant Indian standardprocedures. The test results are tabulated in Table 1. Fromthe grain size distribution curve in Fig. 1, it can be depicted

Table 1Properties of lateritic soil.

S. No. Property Value

1 Consistency limits (%)Liquid limit 56Plastic limit 29Plasticity index 27Shrinkage limit 28

2 Compaction propertiesModified compaction

MDD (g/cc) 1.69OMC (%) 17

Standard compactionMDD (g/cc) 1.63OMC (%) 19.2

3 UCS (kPa)Standard proctor compaction 138Modified compactor compaction 206

4 CBR value (%)Modified proctor compaction

OMC condition 5.26Soaked condition 3.18

Standard proctor compactionOMC condition 3.14Soaked condition 2.04

Plate 1. Arecanut coir.

Table 2Physical properties of Arecanut coir.

Diameter(mm)

Length(mm)

Density(g/cc)

Young modulus(kN/mm2)

Tensilestrength (kN/m2)

0.35 28 1.09 27 2.2

Table 3Chemical composition of Arecanut coir.

Cellulose(%)

Hemicellulose(%)

Lignin(%)

Ash(%)

Pectin(%)

Wax(%)

Nil 35–64.8 13–24.8 4.4 Nil Nil

22 B.M. Lekha et al. / Transportation Geotechnics 2 (2015) 20–29

that the soil consists of 9% gravel, 44% sand, 32% silt and15% clay. As per Indian standard classification the lateriticsoil belongs to SC group (clayey sand) and having a specificgravity of 2.45.

Arecanut coir

Arecanut coir was collected from Puttur, Dakshina Kan-nada District, Karnataka State, India. The dry Arecanutshells, which are brown in color, were collected for thepresent work and the coir from the shell was extractedmanually in the laboratory. Plate 1 shows the physicalappearance of Arecanut coir. The physical and chemicalcompositions of Arecanut coir are tabulated in Tables 2and 3. The aspect ratio and specific gravity of Arecanut coirconsidered for the study are 80 and 0.67 respectively.

0.001 0.01 0.1PARTICLE SIZE (

FIN

E SA

ND

SIZE

SILT

SIZE

CL

AY

SIZE

Fig. 1. Grain size dist

The quantity of coir to be used is an important param-eter. Different quantities of coir can cause different effectin the same soil sample. Insufficient quantity of coir maylead to less stabilization of the soil whereas excess quan-tity may result in ineffective stabilization and decreasethe strength of the soil. Hence, to determine the optimumquantity of coir the CBR and UCS tests were conducted oneach of the soil sample with varying percentages of coir byweight of soil. The different percentages of coir consideredin the present study are listed in Table 4.

05101520253035404550556065707580859095100

1 10

PE

R C

EN

T F

INE

R (

N)

mm)

CO

AR

SE SA

ND

SIZE

GR

AV

EL

SIZE

ME

DIU

M SA

ND

SIZE

ribution curve.

Table 4Dosage of Arecanut coir.

Dosage % by weight of soil Weight per 1 kg of soil (g)

1 0.2 22 0.4 43 0.6 64 0.8 85 1.0 10

B.M. Lekha et al. / Transportation Geotechnics 2 (2015) 20–29 23

Cement

In this investigation, 3% of OPC 43 grade cement, col-lected from the local market, was used based on earlierstudies.

Stabilization using Arecanut coir with 3% cement

The soil mixed with coir does not require any curing asthere is no chemical reaction takes place between soil andcoir. In the present study the soil has been stabilized fur-ther by adding 3% cement to enhance the bonding andstrength. The addition of cement enhances the bondingand friction between soil and coir. The strength of the soilin terms of CBR, UCS and fatigue life has been evaluated for3, 7 and 28 days curing periods.

Sample preparation

The preparation of soil specimens for UCS and CBR testsin laboratory was carried out according to the standard pro-cedure. CBR tests were carried out under both moist andsoaked conditions. OMC, obtained from the modified proc-tor test, was about 17% for plain soil specimens. To preparesoil-coir mixtures, required quantity of Arecanut coir wasadded and thoroughly mixed with dry soil and then waterwas added in two stages to prepare more homogenous spec-imens. In the first stage, half of the water was added to themixture, followed by 15 min continuous hand mixing andthen the remaining water was added, followed by 5 minhand mixing. In the case of soil cement coir mix, dry soil,cement and coir were added and mixed together and thenrequired quantity of water was added. For each mixturespecimens with different dosages, corresponding OMC andMDD was maintained. Samples were cured for varying cur-

Plate 2. Durability samples on We

ing periods by maintaining the moisture content. After com-pletion of curing period, specimens for soaked CBR test wereplaced in water for 4 days and then taken out and allowed todrain before being loaded. In case of field construction, thesoil can be graded first and then it can be mixed with Areca-nut coir and cement in dry state using graders/dozers/rota-vators, etc. (Santoni and Webster, 2001).

Durability test

Durability is defined as the ability of a material to retainstability and integrity over years of exposure to the destruc-tive forces of weathering and hence it is one of the mostimportant factors for any stabilized soil (Dempsey andThompson, 1968). A good stabilizer should help, not onlyin gaining the strength, but also to retain its bonding withsoil during the seasonal changes. Hence, checking durabilityis vital before recommending any stabilizer for practicalapplications. There are mainly two tests for durability –Wet–Dry (WD) and Freeze–Thaw (FT). For the present study,the procedures as per ASTM D559,1996 and ASTMD560,1996 were adopted. Soil specimens with 76 mmheight and 35 mm diameter were prepared and then theywere subjected to 7 days moist curing. The test contains12 cycles of each WD and FT cycles. In wet cycle, specimenswere submerged in water at room temperature for 5 h, thenits dimensions and weight were taken, and in dry cycle, thespecimens were dried at a temperature of 71 �C for 42 h.Then specimens were thoroughly brushed parallel andagain dimensions and weight were taken. This procedureis repeated for 12 cycles. In Freeze cycle, samples wereplaced in water-saturated felt pads and stood on carriersin a freezer at a temperature not higher than –10 �C for22 h. Thawing was done by keeping them in a moistureroom for 22 h and dimensions and weight were taken afterbrushing. The maximum weight loss of specimen for WDand FT should not be more than 14% after 12 cycles. Plate2 depicts the samples during wetting and thawing cycles.

Fatigue test

The fatigue tests were conducted on repeated load test-ing machine shown in Plate 3. All experiments were con-ducted on specimens cured for predetermined period.

t–Dry and Freeze–Thaw test.

Plate 3. Fatigue testing machine.

24 B.M. Lekha et al. / Transportation Geotechnics 2 (2015) 20–29

The loading level in the present study was taken as a frac-tion of the respective UCS value of each specimen at thesame condition of dosages. The untreated and treated soilspecimens with varying curing periods were tested forrepeated loading with 1/3rd, 1/2 and 2/3rd of their UCSvalues.

Test procedure

� The cylindrical specimen (38 mm diameter and75 mm height) was mounted on the loading frameand the deflection sensing transducers (Linear Vari-able Deflection Transducer – LVDT) were set to readthe deformation of the specimen. The load cell wasbrought in contact with the specimen surface.

� In the control unit, through the dedicated software,the selected loading stress level, frequency of load-ing and the type of wave form were fed into theloading device.

� The loading system and the data acquisition systemwere switched on simultaneously and the process offatigue load application on the test specimen wasinitiated.

� The repeated loading, at the designated excitationlevel (i.e. at the selected stress level and frequency)was continued till the failure of the test specimen.

Table 5Pavement design catalog as per IRC: SP: 72-2007 and modified case.

Subgrade strength (CBR) Cumulative ESAL applications

100,000 to 200,000 (T4) 200,000 to 300,

Poor (CBR = 3 to 4%) (S2) 75100100100

75100100

150

Modified (CBR = 20%) 7510075100

75100100

150

Modified subgrade; WBM; granular sub-base;All thickness are in mm.

� The data acquisition system continuously recordedthe vertical deformation of the test specimen withcycles of loading until the failure and the outputwas saved in a result file.

� The failure pattern of the test specimen was visuallyobserved.

Pavement design

The analysis was done using the computer package soft-ware called KENPAVE for pavement design and analysis,developed by Yang (2004) at the University of Kentucky.The KENLAYER computer program applies only to flexiblepavements with no joints or rigid layers. The backbone ofKENLAYER is the solution for an elastic multilayer systemunder a circular loaded area. The software does linear elas-tic multi-layer analysis to obtain the results includingstresses, strains and deflections. It can be applied to lay-ered systems under single, dual, dual-tandem and dual-tri-dem wheel configurations with different layer behaviorslike linear elastic, nonlinear elastic and visco-elastic. Dam-age analysis can be made by dividing each year into a max-imum of 12 periods, each with a different set of materialproperties. Each period can have different loading condi-tions, with single or multiple wheeled. The damage causedby fatigue cracking and permanent deformation in eachperiod over all load groups can be summed up to evaluatethe design life.

There are several input parameters for analysis of pave-ment in KENPAVE and some of them are listed below.

� Number of layers and thickness of each layer� Materials like linear, non-linear, visco-elastic and

combined� Vertical coordinates for analysis� Elastic modulus and Poisson’s ratio of each layer� Response points� Contact pressure, contact radius and spacing of wheels

The pavement structure was adopted fromIRC:SP:72,2007, for a CBR of 3–4% (case S2) and four trafficload cases, as tabulated in Table 5. The structure consists ofa thin bituminous surface course, a WBM layer, a granular

000 (T5) 300,000 to 600,000 (T6) 600,000 to 1,000,000 (T7)

75150

100150

75150

150

15075125

100150

75150

150

125

bituminous treated WBM.

Table 7Variation of UCS with curing period for soil with cement and coir.

B.M. Lekha et al. / Transportation Geotechnics 2 (2015) 20–29 25

base course and a sub-base layer above the subgrade. Forthe analysis, single axle single wheel load was considered;the contact radius and contact pressure on circular loadedarea are 17 cm and 560 kPa. Poisson’s ratio of 0.5 wasadopted for surface layer and 0.4 for WBM, Granular SubBase (GSB) and modified soil layers. Resilient modulus ofsubgrade and granular layers, fatigue and rutting valueswere calculated using Eqs. (1)–(5) recommended by theIRC: 37,2012.

MR ¼ 10� CBR for CBR � 5 ð1Þ

MR ¼ 17:6� ðCBRÞ0:64 for CBR > 5 ð2Þ

MR – Modulus of subgrade (MPa); CBR – California BearingRatio of subgrade (%).

Egb ¼MR � 0:2� h0:45 ð3Þ

Egb – Modulus of granular base (MPa); h – Thickness ofgranular base (mm).

NF ¼ 2:021� 10�4½1=�t�½1=Ebs�0:854 ð4Þ

NF – Number of cumulative standard axles to produce 20%cracked surface area; et – Tensile strain at the bottom ofbituminous surfacing (micro strain); Ebs – Elastic modulusof bituminous surfacing (MPa).

NR ¼ 4:1656� 10�8½1=�z�4:5337 ð5Þ

NR – Number of cumulative standard axles to produce rut-ting of 20 mm; ez – Vertical subgrade strain (micro strain).

For modified design, mixture with soil–3% cement–1%Arecanut coir combination with 19% soaked CBR wasadopted, since it passed durability criteria. Modified pave-ment thickness was arrived using trial and error method.The economic thickness of pavement sections have been

Table 6Compaction test results.

Sample Modified compaction Standard compaction

MDD (g/cc) OMC (%) MDD (g/cc) OMC (%)

Lateritic soil (LS) 1.69 17.0 1.63 19.2LS + 0.2% coir 1.68 19.6 1.63 19.9LS + 0.4% coir 1.66 20.0 1.59 20.5LS + 0.6% coir 1.64 20.6 1.55 21.2LS + 0.8% coir 1.58 21.0 1.51 22.2LS + 1.0% coir 1.47 23.0 1.43 23.8

0

50

100

150

200

250

300

LS LS + 0.2% coir LS + 0.4% coi

UC

S (k

Pa)

Soi

Modified Compaction S

Fig. 2. UCS values for Arecanut treat

decided based on the critical strains, i.e., horizontal tensilestrain at the bottom of bituminous layer and vertical com-pressive strain at the top of subgrade developed in thepavement layers.

Results and discussion

Effect of coir content on compaction

Compaction tests were conducted on lateritic soil rein-forced with different percentages of Arecanut coir for bothmodified and standard proctor cases. The results are tabu-lated in Table 6. It shows that, as the coir percentageincreases, the MDD decreases, due to lateritic soil beingheavy in weight compared with the coir and was replacedby the light weight coir. Therefore, the density of the soilsample decreases. But on the other hand the OMCincreases as the percentage of coir increases, since the coirabsorbs more water.

Effect of coir content on UCS

The tests were conducted for both standard and modi-fied compaction cases. The test results are depicted inFig. 2. As the percentage of coir increased, the UCS valuealso increased up to a certain limit and beyond that itslightly decreased. The results in Table 7 indicate that,the optimum strength was obtained at 0.6% coir and 3%cement content, and further increase in coir leads todecrease in strength.

r LS + 0.6% coir LS + 0.8% coir LS + 1.0% coir

l Mix

tandard Compaction

ed with 7 days curing period.

Dosage UCS (kPa)

3 days 7 days 28 days

M S M S M S

LS + 3% cement + 0% coir 373 288 489 328 540 386LS + 3% cement + 0.2% coir 441 350 520 376 602 485LS + 3% cement + 0.4% coir 532 456 615 495 687 522LS + 3% cement + 0.6% coir 559 502 717 514 896 600LS + 3% cement + 0.8% coir 501 291 608 417 704 519LS + 3% cement + 1.0% coir 475 295 543 383 622 470

LS: lateritic soil; M: modified compaction; S: standard compaction.

MC : Modified compaction; SC : Standard Compaction

0

2

4

6

8

10

12

14

0 0.2 0.4 0.6 0.8 1C

BR

(%

)

Areca nut coir Content (%)

MC at OMC

MC at Soaked

SC at OMC

SC at Soaked

Fig. 3. CBR values for Arecanut coir treated soil with 7 days curing period.

26 B.M. Lekha et al. / Transportation Geotechnics 2 (2015) 20–29

Effect of coir content on CBR

There was an increase in the CBR value as percentage ofcoir increased as in Fig. 3. It is because, the addition of coirimparts some amount of shear resistance to the soil. Theincrease in the strength was less, due to lack of chemicalreaction taking place between Arecanut coir and lateriticsoil. Good improvement in CBR value was observed withconstant dosage of 3% cement from Table 8. As the curingperiod increased, the CBR values also increased and themaximum CBR value was obtained at 0.6% replacementof soil by coir, and then it decreased. Increase in CBR valuemay be because the coir offered better resistance to thepenetration of the plunger. The resistance may be made

Table 8Variation of CBR with curing period.

Dosage CBR (%)

3 days

OMC Soaked

LS + 3% cement + 0.2% coir 30 16LS + 3% cement + 0.4% coir 36 18LS + 3% cement + 0.6% coir 39 24LS + 3% cement + 0.8% coir 31 21LS + 3% cement + 1.0% coir 24 17

Table 9Durability test results for stabilized soil.

No. of cycles Percentage weight loss

Dosage 1 Dosage 2 Dos

W D W D W

LS Collapsed1 �2.04 8.98 �1.78 9.93 �1.2 Collapsed 0.67 12.94 0.3 Collapsed 0.6 Col789101112

up of bond between soil mix. The increase in CBR valuecan also be attributed to the better packing of differentfractions.

Effect of coir content on durability test

The soil–cement–coir mixtures passed the Wet–Dry cri-teria only for mixture with 1.0% coir. Freeze–Thaw samplescould withstand the 12 cycles within 14% weight loss forall mixtures. In general, the coir modification improvedthe durability performance of the mixtures and greaterthe percentage of cement and coir content, the durabilitywas better. The test results are tabulated in Table 9.

7 days 28 days

OMC Soaked OMC Soaked

50 18 51 1954 24 55 2663 40 64 4250 24 52 2545 19 46 20

age 3 Dosage 4 Dosage 5

D W D W D

21 10.23 �1.86 7.69 �2.36 8.9158 11.56 �2.12 8.95 �3.26 9.1694 14.32 1.28 10.24 �2.52 10.72lapsed 5.64 12.38 0.50 13.33

7.61 14.56 1.13 14.689.85 16.58 3.57 19.97

Collapsed 9.67 20.1210.25 21.4511.18 21.9812.66 22.23

Table 10Fatigue test results of cement and Arecanut treated soil.

Stress ratio (%) Standard compaction Modified compaction

UCS (kg) Applied load (kg) No. of failure cycle UCS (kg) Applied load (kg) No. of failure cycle

3% cement + 0% Arecanut coir0.33 45 15 14,098 58 19 36,0240.50 23 13,985 29 35,8760.67 30 13,241 39 35,241

3% cement + 0.2% Arecanut coir0.33 56 19 15,758 60 20 36,4530.50 28 15,023 30 35,9850.67 37 14,322 40 35,324

3% cement + 0.4% Arecanut coir0.33 62 21 25,874 72 24 56,6720.50 31 24,925 36 56,1240.67 41 24,764 48 55,824

3% cement + 0.6% Arecanut coir0.33 71 24 25,965 84 28 66,9470.50 36 25,572 42 66,4520.67 47 24,897 56 66,325

3% cement + 0.8% Arecanut coir0.33 63 21 36,045 73 24 67,0870.50 32 35,982 37 66,9410.67 42 35,421 49 66,547

3% cement + 1% Arecanut coir0.33 56 19 46,125 65 22 77,1040.50 28 46,010 33 76,8540.67 37 45,872 44 76,358

Table 11Displacement values using KENPAVE for conventional and modified soil.

Traffic conditions Vertical coordinate(cm)

Vertical displacement(cm)

C M C M

S2T4 0 0 0.181 0.1547.5 7.5 0.174 0.150

17.5 17.5 0.153 0.13627.5 25 0.134 0.12537.5 35 0.116 0.112

S2T5 0 0 0.177 0.1487.5 7.5 0.170 0.144

17.5 17.5 0.149 0.13027.5 27.5 0.129 0.11942.5 42.5 0.105 0.100

S2T6 0 0 0.160 0.1307.5 7.5 0.153 0.128

22.5 20 0.127 0.11332.5 30 0.112 0.10247.5 45 0.093 0.088

S2T7 0 0 0.144 0.1197.5 7.5 0.139 0.116

22.5 27.5 0.116 0.10237.5 37.5 0.098 0.09052.5 50 0.083 0.078

C – conventional; M – modified.

0

20

40

60

80

S2T4 S2T5 S2T6 S2T7

Ver

tica

l str

ess,

kP

a

Traffic Conditions

Conventional Modified

Fig. 4. Vertical stress values over subgrade for different traffic conditions.

Table 12Damage analysis values for conventional and modified soil.

Traffic conditions Nf (in millions) Nr (in millions)

C M C M

S2T4 16.2 76.2 0.053 0.072S2T5 15.0 67.0 0.122 0.172S2T6 24.4 116.0 0.348 0.526S2T7 30.8 121.0 0.913 1.420

C – conventional; M – modified.

B.M. Lekha et al. / Transportation Geotechnics 2 (2015) 20–29 27

Effect of coir content on fatigue life

Repeated loading test was conducted to determine thefatigue behavior of untreated and treated soil samples.The UCS samples, subjected to 28 days moist curing, weretested at frequency of 1 Hz and rest period of 0.1 s, and theresults are tabulated in Table 10. Fatigue strength is relatedto the number of load cycles that the material can with-stand at a given stress level. Addition of cement and coirto soil increased its fatigue strength significantly. It is

observed that the fatigue life of the soil samples testedwas influenced by the dosage of coir used. At lower stresslevels the specimens exhibited a higher fatigue life andwith further increase in stress level, the fatigue life of sta-bilized specimen reduced considerably.

KENPAVE analysis

In KENPAVE software, thickness of different layers,material properties and loading conditions are provided

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

S2T4 S2T5 S2T6 S2T7

Dam

age

Rat

io (

%)

Traffic Conditions

Conventional Modified

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

S2T4 S2T5 S2T6 S2T7

No.

of

year

s

Traffic Conditions

Conventional Modified

Fig. 5. Variations of design life damage ratio for different traffic conditions.

0.00E+00

5.00E-04

1.00E-03

1.50E-03

2.00E-03

2.50E-03

CS TS CS TS CS TS CS TS

S2T4 S2T5 S2T6 S2T7

Stra

in

Traffic Conditions

Conventional Modified

CS - Compressive StrainTS - Tensile Strain

Fig. 6. Compressive and tensile strain values for different traffic conditions.

Fig. 7. A view of LGRAPH in KENPAVE.

28 B.M. Lekha et al. / Transportation Geotechnics 2 (2015) 20–29

as general input parameters and coefficients of rutting,fatigue, etc. can also be provided for detailed analysis.Damage ratio, the ratio of actual load repetitions to the

allowed repetitions, is a crucial parameter in pavementdesign. In no case, the actual load repetitions shall be morethan the allowed repetitions (i.e., damage ratio greater

B.M. Lekha et al. / Transportation Geotechnics 2 (2015) 20–29 29

than one), which indicates the pavement failure (Deepthiet al., 2013). Stress and displacement values were gener-ated at all the layer interfaces as presented in Table 11.All the stress characteristics were reduced when the con-ventional layers in the standard cases were replaced withthe stabilized soil layers. The results show that the modi-fied stress values are decreased as compared to the con-ventional one, even after reducing the layer thickness. Inthe case of S2T4, even though the thickness is reducedfrom 37.5 to 35 cm for modified pavement structure, thestresses over the subgrade is less than the conventionalpavement and this ensures that the adopted thickness issufficient enough to bear the corresponding traffic loadingpresented in Fig. 4.

Any pavement structure shall sustain only if its sub-grade is located 500 mm above the high flood level inany season. Damage analysis results are presented inTable 12 and Figs. 5 and 6. Table 12 shows that fatigue lifeis much higher than rutting life, which indicates that crit-ical failure of the pavement is due to fatigue. Both com-pressive and tensile strain values are reduced in themodified soil for all traffic conditions. From Fig. 5 it isobserved that the damage ratio is more for conventionalmethod, and its reduction is remarkable in the case of sta-bilized soil. Similarly, design life is also observed to be sig-nificantly enhanced for stabilized soils. Fig. 7 presents theview of LGRAPH in KENPAVE.

Conclusions

Based on the tests conducted in the laboratory the fol-lowing conclusions have been drawn

� Addition of Arecanut coir to the lateritic soilresulted in medium improvement in the soil proper-ties and the optimum content was found to be 0.6%by weight of soil.

� The addition of Arecanut coir along with 3% ofcement by weight of soil resulted in significantincrease in the UCS and CBR values.

� WD and FT cycles caused variations in volume, butit was more significant during drying–wettingcycles.

� Fatigue life was observed to be increased for stabi-lized soil and the enhancement was improving withcoir dosage.

� As per the KENPAVE analysis, the stress and dis-placement values were getting reduced by 6–10%and 4–18% respectively for pavement sections withstabilized soil.

� Enhanced life span of modified pavement structurewas proved from damage analysis, with fatigue lifeand rutting life improvement by 4–5 times and1.4–1.6 times respectively.

� This Arecanut coir soil stabilization will be moreeconomical since it is naturally available as an agri-cultural waste and also only a small amount ofcement is sufficient to achieve the optimum

stabilization. Hence, overall cost of the road con-struction can be reduced while comparing withthe conventional methods.

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