(2006) 110–120www.elsevier.com/locate/enggeo

Engineering Geology 88

Geotechnical properties of tire-cohesive clayey soil mixturesas a fill material

Hasan Cetin a,⁎, Mustafa Fener b, Osman Gunaydin b

a Department of Geology, Çukurova University, Adana, 01330, Turkeyb Department of Geology, Nigde University, Nigde, 51100, Turkey

Received 20 October 2005; received in revised form 1 August 2006; accepted 6 September 2006Available online 20 October 2006

Abstract

Geotechnical properties of pure fine and coarse grained tire-chips and their mixtures (10, 20, 30, 40 and 50%) with a cohesiveclayey soil were investigated through a series of soil mechanical tests in order to investigate possibilities of their usage as alightweight fill material. Grain size and Atterberg limits analysis, permeability, direct shear and compaction tests were performedon the clayey soil, tire chips (both fine and coarse) alone and their mixtures.

The results indicate that the use of used tire-chips mixed with clayey soils as a fill material is possible. The mixtures up to 20%coarse grained tire-chips and 30% fine grained tire-chips can be used above ground water tables where low weight, lowpermeability and high strength are needed in fills such as highway embankments, bridge abutments and backfills behind retainingstructures especially when they are to be built on weak foundation soils with low bearing capacity and high settlement problems.They should not be used where drainage is needed to prevent the development of pore pressures during loading of fills undersaturated conditions. In these cases, they may, however, be used by mixing with high permeability material such as sand and gravel.© 2006 Elsevier B.V. All rights reserved.

Keywords: Rubber tire-chips; Clayey soil; Lightweight fill; Embankment; Abutments; Backfills

1. Introduction

The volume of used rubber auto tires in the world isincreasing every year and their disposal have, therefore,become a major environmental problem worldwide.Every year, millions of scrap tires are either discarded inhuge piles across the landscape or dumped in landfills inlarge volumes. These tire piles not only causeenvironmental pollution but also pose fire and healthhazards. Generally, weighing between 10 and 50 kg,tires are very bulky, and difficult to manage. They are

⁎ Corresponding author. Tel.: +90 322 3386084 / 2079; fax: +90322-3386126.

E-mail address: cetinh@mail.cu.edu.tr (H. Cetin).

0013-7952/$ - see front matter © 2006 Elsevier B.V. All rights reserved.doi:10.1016/j.enggeo.2006.09.002

less dense than other waste items, so they occupy largevolumes in landfills. Rainwater tends to collect instockpiled tires, which then become a breeding groundfor mosquitoes that carry dangerous diseases such asencephalitis. Producing toxic smoke and oils, stockpiledtires are also a fire hazard. Several states in the UnitedStates have, therefore, banned the disposal of used tiresin the land (Masad et al., 1996).

Some of the current uses of scrap tires include rubbermodified asphalt (RMA) for road construction andrunning track, Tire-Derived Fuel (TDF) which is a low-sulfur, high heating-value fuel, remanufactured tires,highway crash barriers, alternative playground bases andplayground equipment, fashion accessories such as ties,shoes, notebook covers, and purses. However, these uses

Table 1Some properties of the clayey soil

Properties Clayey Soil

Liquid limit (%) 41.6Plastic limit (%) 25.7Shrikage limit (%) 21.3Plasticity index (%) 15.9Specific gravity 2.72Grain sizes (%)

Gravel 0.0Sand 7.8Silt 31.5Clay 60.7

Soil type (USCS) CLDescription Silty clay

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are still not enough to consume the large quantities of scraptires generated every year. The majority of scrap tiresespecially in developing countries are, therefore, eitherstockpiled, landfilled or dumped in the country illegally.

Lately, several researchers have been undertaken inorder to study possibilities of using tire-chips in civilengineering applications such as highway embankmentsand backfills behind retaining structures over weak orcompressible soils. According to Humphrey (1999),using tire-chips in civil engineering applications areadvantageous because of their low density, highdurability, high thermal insulation and in many casesleast cost compared to other fill materials. Previousstudies have mainly concentrated on determiningengineering properties of pure tire-chips and/or variousmixtures of tire-chips with sand as a lightweight fillmaterial (Ahmed, 1993; Edil and Bosscher, 1994;University, 1995; Foose et al., 1996; Masad et al.,1996; Wu et al., 1997; Lee et al., 1999; Yang et al.,2002; Youwai and Bergado, 2004). They concluded thattire-chips and sand mixtures can be used as a lightweight

Fig. 1. Particle size distribution curves for the cla

fill material behind retaining structures and highwayembankments over weak or high compressibility soilsand further studies are needed to investigate the use ofdifferent tire-chips sizes and percentages with varioustypes of soils.

Conventional highway embankment and retainingwall fill materials in practice may, however, include con-siderable amount of fines. The aim of this study is, there-fore, to determine geotechnical properties of pure fine andcoarse grained tire-chips and their various mixtures with aclayey (cohesive) soil as a lightweight fill material inhighway embankments, bridge abutments and backfillsbehind retaining structures. Usage of tire-chips espe-cially in highway embankments will have a positiveimpact on the environment since large quantities can beconsumed in these voluminous structures.

2. Materials and methods

2.1. Sample preparation and index property testing

Samples were prepared by mixing a cohesive clayey(CL type) soil with 10, 20, 30, 40 and 50% coarse andfine grained tire-chips free of steel belts by weight(Table 1 and Fig. 1). Percentages of mixtures by volumeare shown in Table 2. Fine tire-chips were under0.425 mm (No. 40 sieve) and coarse tire-chips werebetween 2 mm (No. 10 sieve) and 4.75 mm (No. 4 sieve)in size (Fig. 1). This is needed to study effect of fine andcoarse tire-chips separately since, similar to fine andcoarse grained soils, they may behave differently. Theclayey soil was locally obtained from the Guvencformation of Miocene age (Schmidt, 1961) outcroppingin the Adana basin in southern Turkey. The tire-chipswere obtained from a local tire manufacturing plant.Effects of tire-chips on the geotechnical properties of

yey soil, fine and coarse grained tire-chips.

Table 2Compositions of mixtures by weight and volume

By weight (%) By volume (%)

Pure clay (0% fine tire-chips) Pure clay10% fine tire-chips 18% fine tire-chips20% fine tire-chips 33% fine tire-chips30% fine tire-chips 46% fine tire-chips40% fine tire-chips 57% fine tire chips50% fine tire-chips 66% fine tire-chips100% fine tire-chips 100% fine tire-chips10% coarse tire-chips 25% coarse tire-chips20% coarse tire-chips 42% coarse tire-chips30% coarse tire-chips 55% coarse tire-chips40% coarse tire-chips 66% coarse tire-chips50% coarse tire-chips 74% coarse tire-chips100% coarse tire-chips 100% coarse tire-chips

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this cohesive clayey soil were investigated through aseries of soil mechanical tests.

Grain size analysis and Atterberg limits tests wereperformed in order to classify both the clayey soil and themixtures according to the Unified Soil ClassificationSystem (USCS). Atterberg limits tests were performedonly on the clayey soil and the fine tire-chip mixturessince they are performed only on soil fraction passingNo:40 (0.425 mm) sieve and the coarse grained tire-chipsused in this study would be retained on this sieve. Thetests were performed following the American Society ofTesting Materials (ASTM) D 422-63, D 4318-00 andD 427-98 (2003), respectively.

2.2. Permeability testing

The behavior of fills under saturated conditions isgreatly influenced by the drainage characteristics of the fill

Fig. 2. Changes of liquid limit, plastic limit, plasticity in

materials used (Cedergren, 1989). Therefore, using fallinghead method, permeability tests were conducted on theclayey soil and mixtures in a consolidation test apparatussetup. The samples were cylindrical in 2.85 cm height and6.35 cm diameter, and were saturated prior to measuringpermeability by applying headwater pressure in agraduated glass burette connected to the bottom portionof the consolidometer. The permeability values weredetermined at normal pressures of 46, 93, 185, 287 and370 kPa simulating various possible overburden pressures.

2.3. Shear and deformation testing

The behavior of fills also depends on the strength anddeformation characteristics of the fill materials used.Consolidated undrained direct shear tests (or consoli-dated quick, Qc, tests) were performed to determine theshear strength and vertical or volumetric strain char-acteristics of the clayey soil and the mixtures undervarious normal pressures. Smaller additional normalpressures were used in order to secure the shapes of thefailure envelopes at lower normal pressures for both thefine and coarse grained tire-chip mixtures alone.

The tests were performed under saturated conditionsas described in Lambe (1951) and Liu and Evett (1984)or similar to the consolidated drained tests (or slow, S,tests) of the ASTM D 3080-98 (2003) except that afaster shear rate (1 mm/minute) was used so that thedrainage is non or minimal. Complete prevention ofdrainage in direct shear tests is very difficult. Therefore,the great majority of so-called undrained tests in directshear test machines are not completely undrained; thelarger the applied normal load, the greater the tendencyfor drainage (Lambe, 1951).

dex and clay content as the % tire-chips increases.

Fig. 3. Relationship between coefficient of permeability and normal pressure for (a) fine-grained, (b) coarse-grained tire-chip mixtures and the clayeysoil alone.

Fig. 4. Relationship between coefficient of permeability and normal pressure for pure fine-grained and pure coarse-grained tire-chips.

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Fig. 5. Shear stress versus horizontal displacement and vertical deformation curves for (a) the clayey soil and (b–f ) fine-grained tire-chip mixtures.

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Fig. 6. Shear stress versus horizontal displacement and vertical deformation curves for (a) the clayey soil and (b–f ) coarse-grained tire-chip mixtures.

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The tests were performed on a direct-shear device(ELE D-300) with a 6 cm x 6 cm square and 3.5 cmheight shear box seated in a pan which was filled withwater and kept full during the tests.

2.4. Compaction testing

Stability and settlement of an earth-fill structure suchas an highway embankment and bridge abutment dependson how well the fill material is compacted. If the fillmaterial, for example, is dumped or otherwise placed atrandom in a fill, the result will be an embankment withlow stability and high settlement (Holtz and Kovacs,1981). Therefore, following ASTM D 698-00a (2003),standard proctor (compaction) tests were run to determinefirst the compaction characteristics of the clayey soilalone, then, for comparison, for both the fine and coarsetire-chip mixtures. The optimummoisture contents (Wopt)at which the dry unit weights or densities (γdry), therefore,compactions, are greatest were determined.

3. Results and discussions

3.1. Index property analysis

The soil indices and grain size curve of the clayeysoil are given in Table 1 and Fig. 1, respectively. Accor-ding to the USCS, the clayey soil classifies as a CL typesoil, with medium plasticity. The majority of the clayminerals are smectites and the remainder are palygors-kites and kaolinites (Sayarslan et al., 1997). The clayeysoil alone has 60.70% clay content which decreasegradually as the tire-chips are added. It, for example,

Fig. 7. Shear stress versus fine-grained

becomes 30.35% at the 50% fine tire-chip mixture byweight. Accordingly, the Atterberg limits are expectedto decrease. Interestingly, the liquid limit (41.55%) staysabout the same up to 30% then it starts to decrease whilethe plastic limit (25.67%) stays about the same up to10% from which point on it shows some amount ofdecrease up to 20% then stays about the same (Fig. 2).These results are similar to those of typical fine grainedcohesive soils with medium plasticity.

3.2. Permeability tests

The behavior of an embankment under saturatedconditions is greatly influenced by the drainagecharacteristics of the fill material used (Cedergren,1989). Awell-drained material will prevent the develop-ment of excess pore pressures during loading of fills andalso accelerates consolidation of underlying low per-meability foundation soils by providing a drainage path,thereby enhancing the stability of structures (Cedergren,1989; Ahmed, 1993).

The permeability tests were conducted on the pureclayey soil, fine and coarse tire-chips and the mixturesunder different loading conditions in a consolidation testapparatus setup. The samples were saturated prior tomeasuring permeability. The permeability values weredetermined at normal pressures of 46, 93, 185, 287 and370 kPa simulating various possible overburden pres-sures and the results are shown in Fig. 3. The per-meabilities of the clayey soil alone and all the mixturesare low (x10−7 – 10−8 cm/s) which are consistent withtypical low permeability clayey soils. Effects of both thefine and coarse-grained tire-chips and the normal

and coarse-grained % tire-chips.

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pressures on the permeability are similar. The perme-abilities increase as the % tire-chips increases and thenormal pressure decreases. The higher the % tire-chipsand the lower the normal pressure the higher the dif-ference in the increase is.

These results indicate that the mixtures can be usedwhere low permeability and density (or loading) areneeded in fills on weak foundation material such asalluvium. They should not be used where drainage isneeded to prevent the development of pore pressuresduring loading of fills under saturated conditions. Theymay, however, be used by mixing with high permeabil-ity material such as sand and gravel. They may also beused in unsaturated conditions where drainage is notneeded, for example, in highway embankments andbackfills behind retaining structures when they are to bebuilt above ground water tables.

Fig. 8. Failure envelopes of (a) fine-grained, (b) coarse-grained tire-

The permeabilities of both the fine and coarse-grained tire-chips alone are high (x10−3–10−4 cm/s)which are typical of sands (Fig. 4). Masad et al. (1996)found similar results and suggested that such highvalues of permeability render the use of tire-chips aloneor in combination with sand as a useful fill material inembankments.

3.3. Direct shear tests

Consolidated undrained direct shear tests wereperformed to determine the shear strengths and verticalor volumetric strain characteristics of the clayey soil,tire-chips (both fine and coarse) alone and the mixturesunder different normal pressures. The shear stress versushorizontal displacement curves are shown in Figs. 5and 6. As seen here, almost all the samples showed a

chip mixtures as well as pure clayey soil and tire-chips alone.

Fig. 9. Change of (a) cohesion, (b) angle of internal friction as % tire-chips (fine and coarse) increase.

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stress-hardening behavior, in other words, there were noclear drops, therefore, no pronounced peaks (failurepoints) on the slopes of the curves. In these cases, it issuggested that 10–20% shear deformation should betaken as the failure point (Liu and Evett, 1984; ASTMD 3080-98, 2003). Studying soil structure changesduring drained and undrained shear of a cohesive sandysilt–clay soil showing a stress-hardening behavior, Cetinand Söylemez (2004) showed that the failure of suchsoils occur at 15% shear deformation. The shearstrengths were found by taking the 15% shear deforma-tion (in our case 9 mm) as the failure point. The shearstresses at failure versus % tire-chips (fine and coarse)under different normal pressures are shown in Fig. 7. Asseen here, there is a clear increase in the shear strengthsup to at least 30% for fine and 20% for coarse tire chipmixtures. For example, 110 kPa shear strength of thepure (0% mixture) clayey soil under the normal pressureof 327 kPa increases to 181 kPa for the coarse and140 kPa for the fine tire-chip mixtures at 20% and 30%,respectively. Also, the shear strengths increase as thenormal pressures increase.

The failure envelopes, the cohesion and angle ofinternal friction versus % fine and coarse tire-chipmixtures are shown in Figs. 8 and 9. Cohesion increasesas the % of tire-chips increase up to 40% for both fineand coarse mixtures while the angle of internal frictiondecrease. In other words, the more chips are added, themore cohesion and the less angle of internal friction areachieved until 40% tire-chips content. For example,19 kPa cohesion of the pure clayey soil (0% mixture)increases to 54 kPa for the fine and 56 kPa for the coarsetire-chip mixtures at 40%. The 21 ° angle of internalfriction of the clayey soil (0% mixture), on the otherhand, decreases to 10 ° for the fine and 15 ° for thecoarse tire-chip mixtures at 40%. From 40% on,however, while the cohesion decreases, the angle ofinternal friction increases. The failure envelope firstrotates clockwise until 40% tire-chip mixtures, then itrotates anticlockwise for both type of mixtures.

Figs. 5 and 6 also show the volumetric (vertical)strain versus horizontal shear strain characteristics. Thevertical strain values under the selected normal pres-sures for the clayey soil alone are all negative or com-pression is taking place which is consistent with typicalnormally consolidated clayey soils (Figs. 5a and 6a).

The fine and coarse tire-chips mixtures under thenormal pressure of 54 kPa does not show considerablevertical strains or volume change during shear; slightlynegative vertical strain (compression) for the clayey soilalone becomes nearly zero or slightly positive (dilation)(Figs. 5b–f and 6b–f ). However, originally high

negative vertical strains for the clayey soil alone underhigher normal pressures such as 327 kPa either decreaseconsiderably for the fine tire-chip mixtures or becomeslightly above zero or positive for the coarse tire-chipsmixtures as the percent tire-chips increases up to 50%.In general, the addition of both fine and coarse tire-chipsseem to decrease vertical strains especially under highernormal pressures. As the % tire-chips increase, the finegrained tire-chip mixtures seem to behave like finegrained clayey soils while the coarse grained tire-chipmixtures seem to behave similar to coarse-grained soilssuch as sands.

The direct shear test results indicate that the mixturesup to 20% coarse grained tire-chips and 30% finegrained tire-chips have high shear strength character-istics (higher than the clayey soil alone) in terms of shearstrengths, cohesion and angle of internal friction;therefore, can be used as fill material.

3.4. Compaction tests

Standard proctor (compaction) tests were run to de-termine the compaction characteristics of the clayey soil

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alone as well as the fine and coarse tire-chip mixtures.Optimum moisture contents (Wopt ) at which the dry unitweights or densities (γdry) are highest were determinedfirst for the clayey soil alone, then, for comparison, forboth the fine and coarse tire-chip mixtures. The resultsare shown in Fig. 10. For the clayey soil alone, the

Fig. 10. Standard proctor test curve for the clayey soil alone and forfine (a) and coarse (b) grained tire-chips mixtures. The curve for theclayey soil alone was plotted on both a and b for comparison.

maximum dry unit weight (γdry) of 15.79 kN/m3 isobtained at the optimum moisture content (Wopt) of19%. The dry unit weights for both the fine and coarsetire-chip mixtures decrease as the percent tire-chipsincrease. They, for example, become 13.43 kN/m3 and12.50 kN/m3 for the suggested upper limit mixtures of20% coarse grained tire-chips and 30% fine grained tire-chips, respectively. The results indicate that the drydensities of the tire-chip mixtures are less than the drydensity of typical soils including the clayey soil used inthis study. Such values show a good potential for usingthe tire-chips as lightweight fill material.

4. Conclusions

The results indicate that the shear strengths increaseup to 30% for fine and 20% for coarse tire chip mixtures.The higher the normal pressure the higher the shearstrength. Cohesion increases as the % of tire-chipsincrease up to 40% for both fine and coarse mixtureswhile the angle of internal friction decrease. After 40%,however, while the cohesion decreases, the angle ofinternal friction increases.

As the percent tire-chips increases, the fine andcoarse tire-chips mixtures under lower normal pressuresdo not show considerable vertical strains or volumechange during shear. However, under higher normalpressures, originally high negative vertical strains forthe clayey soil alone decrease considerably for the finetire-chip mixtures or become slightly above zero orpositive for the coarse tire-chips mixtures up to 50%.Especially under higher normal pressures, the additionof both fine and coarse tire-chips seem to decreasevertical strains.

The permeabilities of the clayey soil and the mixturesare consistent with typical low permeability clayey soils.The permeabilities increase as the normal pressuredecreases and the % tire-chips increases. The permeabil-ities of both the fine and coarse-grained tire-chips aloneare typical of sands which renders the use of tire-chipsalone or in combination with sand as a useful fill materialin embankments.

The compaction test results indicate that the drydensity of the tire-chip mixtures are less than the drydensity of typical soils including the clayey soil used inthis study. Such values show a good potential for usingthe tire-chips as lightweight fill material.

Finally, the results indicate that the mixtures up to20% coarse grained tire-chips and 30% fine grainedtire-chips can be used above ground water tables wherelow weight, low permeability and high strength areneeded in fills such as highway embankments, bridge

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abutments and backfills behind retaining structuresespecially when they are to be built on weak foundationsoils with low bearing capacity and high settlementproblems. They should not be used where drainage isrequired to prevent the development of pore pressuresduring loading of fills under saturated conditions. Inthese cases, they may, however, be used by mixing withhigh permeability material such as sand and gravel. Asalso suggested by Masad et al. (1996), proper soil coveris needed on top and sides of embankments for safetyagainst fire. Usage of tire-chips in this way will have apositive impact on the environment since large quantitiescan be consumed in these voluminous structures.

Acknowledgement

Part of this study was financially supported by theÇukurova University Research Foundation (Project No:FBE.97YL.96). The authors thank two anonymousEngineering Geology reviewers for their critical reviewof the manuscript. Their invaluable comments improvedthe manuscript considerably. We would also like tothank Aysun Serin and Hikmet Senbayrak for their helpin soil mechanics tests and Mustafa Laman for pro-viding unlimited access to the soil mechanics laboratoryof the Civil Engineering Deparment at ÇukurovaUniversity.

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