MODEL STUDIES ON GEOFIBER-REINFORCED SOIL

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1 IGC 2009, Guntur, INDIA MODEL STUDIES ON GEOFIBER-REINFORCED SOIL B.V.S. Viswanadham Professor, Department of Civil Engineering, Indian Institute of Technology Bombay, Powai; Mumbai , India. ABSTRACT: The objective of this paper is to present the effect of discrete and randomly distributed geofibers in: i) restraining cracking tendency of clay barrier subjected to differential settlements, ii) reducing swelling tendency of moistcompacted expansive soil, and iii) Efficacy of geofiber-reinforced soil as a fill material through laboratory model studies. For this purpose, a number of experiments were carried-out for determining the influence of geofibers having various dosages and length. Two types of geofibers namely polypropylene and polyester fibers were used. Three types of soils were used. Based on the analysis and interpretation of model studies on geofiber-reinforced soil, the mechanism of discrete fiber reinforcement in restraining cracking, swelling and potential of geofiber-reinforced soil as a fill material of soil could be explained. It can be clearly stated that the geofiber-reinforced soil is a very effective method and which helps to restrain cracking of clay barrier at the onset of differential settlements, to use the expansive soil deposits at the construction sites, and to promote geofiberreinforced soil as a fill material. However, one of the key issues to be focused for successful implementation of technique in the field is in evolving at a methodology for mixing geofibers with soil. 1. INTRODUCTION The concept of reinforcing soil masses by including some kind of fiber was practiced by early civilizations which used soil mixed with straw or other available fiber to improve durability and strength of the dried brick used as building materials. They found that fibrous soil works better than natural soil. Reinforced soils can be obtained by either incorporating continuous reinforcement inclusions (e.g., sheet, strip or bar) within a soil mass in a defined pattern (i.e., systematically reinforced soils) or mixing discrete fibers randomly with a soil fill (i.e., randomly reinforced soils). However, randomly distributed fiber reinforced soils have recently attracted increasing attention in geotechnical engineering. In comparison with systematically reinforced soils, randomly distributed fiber reinforced soils exhibit some advantages. Preparation of randomly distributed fiber reinforced soils mimics soil stabilization by admixture. Randomly distributed fibers offer strength isotropy and limit potential planes of weakness that can develop parallel to oriented reinforcement. Past research has demonstrated that the inclusion of randomly distributed discrete fibers significantly improve the engineering response of soils (Maher & Ho 1994; Rodatz & Oltmanns 1997; Nataraj & McManis 1997; Ziegler et al. 1998; Puppala & Musenda (2000); Miller & Rifai 2004; Viswanadham et al. 2006; Cai et al. 2006, Sivakumar Babu & Vasudevan. 2008a 2008b, Das et al. 2009; Viswanadham et al. 2009a, 2009b, and 2009c). Maher & Ho (1994) studied the mechanical properties of a kaolinite/fiber soil composite. Fiber types used were polypropylene and fiber glass. The study showed that fibers increased the shear strength of the soil and also increased ductility of kaolinite. In addition, increasing water content reduced the contribution of fibers to composite strength and ductility. The study also showed that increasing fiber content increases the hydraulic conductivity of the soil, for the same fiber types and lengths tested. Polypropylene fibers were used to reduce tension cracks and the amount of shrink/swell in compacted clay. It was observed that the inclusion of fibers increased the tensile strength and hydraulic conductivity of clay and provides ductile behavior to material, but increase was more prominent at higher fiber contents (Maher & Ho 1994 & Ziegler et al. 1998). Nataraj & McManis (1997) reported that the soil reinforced with fiber is able to hold together more deformation and subsequently higher stresses at rupture. Ayyar et al. (1989) have reported about the efficacy of randomly distributed coir fibers in reducing the swelling tendency of the soil. The efficacy of combination of fly ash and polypropylene fibers in reducing swelling and shrinkage characteristics was also reported (Puppala & Musenda 2000; Punthutaecha et al. 2006). Puppala & Musenda (2000) and Punthutaecha et al. (2006) showed that fiber reinforcements enhanced the unconfined compressive strength and reduced the swelling potential of expansive clays. Cai et al reported an increase in fiber content led to reduction in swelling potential of lime stabilized clayey soil. Viswanadham et al. 2009b & 2009c have reported about the efficacy of randomly distributed polypropylene tape fibers in reducing the swelling tendency of the expansive soil. Use of Discrete and Randomly Distributed Fiber (DRDF) reinforcement technique to decrease a soil's crack potential can be explored as one of the viable techniques to address the problem of cracking of compacted clay barrier at the onset of non-uniform settlements. This technique was investigated earlier by Rodatz and Oltmanns (1997) to develop as a new 947

2 liner construction material for landfill covers, especially when high mechanical and thermal loadings are anticipated. Miller & Rifai (2004) have explored to evaluate the affect of discrete and randomly distributed fibers on the tensile strength-strain characteristics of clayey soil and to restrain desiccation cracking in compacted clay barriers of waste containment systems. Very recently, Viswanadham et al. (2006) & Viswanadham et al. (2009a) have evaluated the influence of discrete and randomly distributed fibers on the integrity of clay based landfill covers subjected to non-uniform settlements. Their results indicate the fiber reinforcement has significant potential in restraining cracks and restricting the propagation of cracks across the depth of the clay barrier. Failure of geotechnical structures, such as levees, dams, vertical cuts, embankments etc. is very common and in most of the cases causative force behind these is seepage. Efficacy of fiber reinforcement in reducing the seepage velocity and improving the piping resistance of soils investigated by Sivakumar Babu & Vasudevan (2008a) and Das et al As discussed, use of discrete and randomly distributed fiber reinforcement technique has significant effect on the engineering response of soils. Past research has demonstrated that the inclusion of randomly distributed discrete geofibers (flexible polymeric fibers) significantly improve the engineering response of soils. However, further work in this direction is limited. This paper presents studies enveloping the effect of discrete and randomly distributed geofibers in restraining: i) cracking tendency of clay barrier subjected to differential settlements, ii) swelling tendency of moist-compacted expansive soil, and iii) efficacy of geofiber-reinforced soil as a fill material through laboratory model studies. 2. MODEL STUDIES ON GEOFIBER-REINFORCED SOIL In this paper, for the model studies on geofiber-reinforced soil (Sections 2.1 and 2.3), a large beam centrifuge available at IIT Bombay was used. A geotechnical centrifuge can be used to perform tests on models that represent full-scale prototypes under normal field conditions. A 1/N scale model tested at a centrifugal acceleration N times the earth s gravity (g) experiences stress conditions identical to those in the prototype. The above technique of modeling in geotechnical engineering can be extended to model compacted clay barriers reinforced with randomly distributed discrete fibers, with an aim to study the response of randomly reinforced soil liners subjected to continuous non-uniform deformations created artificially in the centrifuge. Centrifuge modeling was essential in this regard because the cracking of the soil liner is highly influenced by the presence of prototype stress conditions. Hence, the application of this technique to the present context of study is regarded to be more relevant. The 4.5 m radius large beam centrifuge at Indian Institute of Technology Bombay (IIT Bombay), India was used in the present study. The centrifuge capacity is 250 g-ton with a maximum payload of 2.5 t at 100 g and at higher acceleration of 200 g the allowable payload is t. The centrifuge has a swing basket at one end and an adjustable counterweight at the other end. 2.1 Effect of Fiber Reinforcement on the Integrity of Clay Barriers Although compacted clay barriers are most widely used all over the world (wherever clays are abundantly available), very few attempts have been made to evolve at a viable solution to retain their integrity at the onset of non-uniform settlements. In the recent past, the interest of using fibers has arisen to improve compacted clay performance as hydraulic barriers without changing physical properties of soil. Figure 1 presents a schematic representation of a deformed geofiberreinforced clay barrier of landfill cover at the onset of different settlements (of the order of s 1, s 2,). Generally, compacted clay barriers with thickness ranging from 0.6 m 1.5 m are provided along with a cover soil (including drainage layer of 0.3 m thickness) of 1.5 m thickness in landfill covers. Use of Discrete and Randomly Distributed Fiber (DRDF) reinforcement technique to decrease a soil's crack potential can be explored as one of the viable techniques to address the problem of cracking of CSL at the onset of non-uniform settlements. This technique was investigated earlier by Rodatz & Oltmanns (1997) to develop as a new liner construction material for landfill liners, especially when high mechanical and thermal loadings are anticipated. However, further work in this direction is limited. Very recently, Miller & Rifai (2004) and Viswanadham et al. 2009a have explored to evaluate the affect of discrete and randomly distributed fibers on the tensile strength-strain characteristics of clayey soil and to restrain desiccation cracking and cracking due to bending in CCLs of waste containment systems. In this section, assuming that identical fibers are used in both centrifuge model and in the field (Viswanadham et al. 2009a), the significance effect of fibers in restraining cracking of clay barrier at the onset of bending was demonstrated through centrifuge model tests. Landfill cover Geofiber-reinforced clay barrier Fig. 1: Schematic Cross-Section of Geofiber-Reinforced Clay Barrier Subjected to Differential Settlements 948

3 The model soil barrier material was found to have a liquid limit of 38%, plastic limit of 16%, coefficient of permeability of m/s, maximum dry unit weight of 15.9 kn/m 3 and optimum moisture content of 22% (standard Proctor compaction test). The selected soil is classified as CL type according to Unified soil Classification system. Polypropylene tape fibers 1.2 mm width, mm thickness, breaking load of N, and 22% elongation at break were used. A fiber dosage of 0.5% by dry weight of soil and aspect ratio of 45 was used. This was fixed based on the results reported by Viswanadham et al. (2009a). Aspect ratio is defined as ratio of length to breadth of the fiber. This implies that the aspect ratio of 45 indicates 90 mm long fibers. Detailed discussion of on model preparation and test procedure are discussed in detail by Viswanadham et al. (2009a). Figure 2 shows front elevation of the model before commencement of centrifuge test. Centrifuge tests were performed at 40 g by subjecting the model to a constant angular velocity of 93 revolutions per minute. 25 mm (1.0 m in prototype dimensions), in the case of geofiber-reinforced clay barrier, partial penetration of cracks at the zone of maximum curvature can be noted. Figure 4 presents variation of maximum outer fiber strain with radius at the zone of maximum curvature for models SSL4 and BFL2. As can be noted, the geofiber reinforced clay barrier was observed to have strain at crack initiation of 1.52% and sustain large non-uniform settlements. In the case of unreinforced clay barrier, the strain at crack initiation was observed to be only 0.65% and observed to crack at radius of 170 m itself. This brings out the significant potential of fiber reinforcement in not only restraining cracking of clay barrier but also limiting the penetration of cracks extending up to mid-depth only. The inclusion of fibers as a reinforcing material affected the deformation behaviour of compacted soil liner compliance to non-uniform settlements. The improved soil-fiber mix enhances the function of soil liners and covers as hydraulic barriers for waste containment systems of landfills by decreasing the cracking potential. Fig. 2: Front Elevation of Prepared Centrifuge Model before Centrifuge Test (model: BFL2) Controlled in-flight simulation of non-uniform settlements of landfill in a geotechnical centrifuge was carried out using a trap-door arrangement. Digital image analysis technique was found to be very useful in arriving at strain at crack initiation and in understanding the propagation of cracks in clay barrier with and without geofiber reinforcement subjected to nonuniform settlements. In this section, results of two models, namely SSL4 and BFL2 were discussed. Both the models were moist-compacted at it maximum dry unit weight and optimum moisture content and were tested without any cover soil. Though cover soil imposes a confinement of the order of 20 kpa, in order to observe the strain at crack initiation and crack propagation in the clay barrier with and without fiber reinforcement, presence cover soil was not considered. In the case of model BFL2, the model soil barrier was mixed randomly with fibers with a dosage of 0.5% and having length of 90 mm was used. Long fibers were considered to prevent pull-out failure (Viswanadham et al. 2006, 2009a). Figure 3 presents status of un-reinforced and geofiber reinforced clay barrier cross-sections at the end of centrifuge test. Even after subjecting to a central settlement equal to Fig. 3: Status of Un-Reinforced and Geofiber Reinforced Clay Barriers at the End of Centrifuge Test Strain (%) Geofiber-reinforced clay barrier SSL4 BFL2 SSL4 (crack initiation) BFL2 (crack initiation) Un-reinforced clay barrier Radius at the zone of maximum curvature (m) Fig. 4: Variation of Maximum Outer Fiber Strain with Radius at the Zone of Maximum Curvature 949

4 2.2 Use of Fibers for Restraining Swelling Tendency of Expansive Soil The fiber begins to be used as an admixture for restraining swelling of expansive soils, which was based on encouraging results obtained from tests on fiber-reinforced clay soil. Discrete and randomly distributed coir fibers restrained swelling effectively (Viswanadham 1989). Punthutaecha et al. (2006) studied the efficacy of combination of fly ash and polypropylene fibers in reducing swelling and shrinkage characteristics. Cai et al. (2006) reported that an increase in fiber content reduced heave and brittleness of lime-stabilized expansive soils. Fiber-reinforcement of expansive soils reduced swell potential (Puppala & Musenda 2000). Very recently, Viswanadham et al. (2009b) reported that fibers were effective in reducing the swelling pressure and swell potential of clayey soils significantly. The soil used in the experimental investigation had a free swell index (FSI) of 93%. It was collected from a depth of 1.5 m in Pune, Maharashtra, India. The soil was found to have a specific gravity of 2.72, liquid limit of 71%, plasticity index of 41% and shrinkage limit of 12%. The X-ray diffraction spectra gave the following mineralogical composition: montmorillonite - 48 to 50%, quartz - 30 to 32%, calcite % and anatase - 1 2%. The total cation exchange capacity of the soil was 47.5 meg/100 g. Based on the plasticity properties, the soil was classified as CH according to Unified Soil Classification System. The fiber used for reinforcing the expansive soil specimens was a polypropylene fiber and were similar to those described in Section 2.1. The fiber content f was varied as 0%, 0.25% and 0.50% by dry weight of expansive soil. The length of the fibers was varied as 30 mm, 60 mm and 90 mm. 1-D Swell tests were conducted on un-reinforced and fiber-reinforced expansive soil samples in the laboratory. The clay-fiber blends were prepared at their respective OMC and MDD. For compaction of blends at the respective OMC and MDD, the required weight of fibers along with the required weight of the oven-dry soil was used. A twin semi-circular shaped fabricated mould with a front Perspex sheet was developed for testing. Digital imaging technique was used to observe heave of the soil in both un-reinforced and fiberreinforced conditions. Displacement profiles obtained from image analysis were used for interpreting swell or upward movement profiles of the specimens. Heave observed in the digital image analysis was compared with that obtained from dial gauge readings. Reduction in heave was directly proportional to fiber content and fiber length. Figure 5 shows the variation of heave of horizontal planes H/3 and 2H/3 from the bottom of the tube specimens with fiber length for different fiber contents (0.25% and 0.50%). At H/3, vertical movement was better controlled at lower fiber lengths itself when the fiber content was higher (0.50%). However, at a smaller dosage of fiber (0.25%), higher fiber length was needed for effective control of heave. A fiber dosage of 0.25% at a higher fiber length was found to have given better results (see Fig 5). The points corresponding to 2H/3 were lying above those corresponding to H/3 for all cases because heave would be higher in the top layers of the soil. Figure 6 presents relationship between fiber reinforcement effect ratio and fiber length for two fiber contents (f = 0.25% and f = 0.50%). Fiber reinforcement effect ratio I fr is defined as a ratio of heave in reinforced to unreinforced sample. As can be seen from Figure 6, for a fiber content equal to 0.25% by dry weight of the soil, fiber reinforcement effect ratio was found to be 2.5 for a fiber length l equal to 60 mm. For f = 0.5%, the fiber reinforcement effect ratio was found to be close to 3 for a fiber length equals to 30 mm. An approximate trend was indicated for a fiber content of 0.5% through a broken line in Figure 6. Relationship between fiber reinforcement effect ratio I fr with fiber length suggests that for a fiber content of 0.25%, 60 mm long fibers H = thickness of soil sample Fig. 5: Variation of Heave Measured Through Digital Image Analysis with Fiber Length at 48 Hours (after Viswanadham et al. 2009c) Fig. 6: Variation of I fr with Fiber Length (after Viswanadham et al. 2009c) 950

5 were required and for a fiber content of 0.50%, 30 mm long fibers were required to have a maximum benefit of fiber reinforcement in restraining heave of expansive soil deposits. One of the alternatives to construct new pavements on expansive soil subgrades is to replace with a well-graded soil having good strength characteristics. However, if the volume of the expansive soil to be removed is large, then it turns out to be highly uneconomical and not feasible from environmental considerations. In such situations, use of optimum combinations for length and dosage of fibers appears to be a viable methodology to reuse existing expansive soils. Reduction in heave was the maximum at low aspect ratios at both the fiber contents of 0.25% and 0.5%. Test results revealed that fiber length is a key factor that influences the reinforcing effect of fiber. Discrete and randomly distributed fibers were found efficacious in reducing heave. More details pertaining to this topic are presented by Viswanadham et al. 2009c. 2.3 Efficacy of Geofiber-Reinforced Soil as a Fill Material Failure of geotechnical structures, such as levees, dams, vertical cuts, embankments etc. is very common and in most of the cases causative force behind these is seepage. Due to raise of ground water table, pore water pressure increases or it can be said that the negative suction in the soil decreases and consequently shear strength of soil slope decreases. Therefore it is extremely important to evolve at a proper slope stabilization technique to protect these geotechnical structures. With an aim to develop an alternative fill material using a soil prone to seepage, use of discrete and randomly distributed fiber inclusions to restrain seepage induced slope failure is explored. Several researchers, like Gray and Ohashi 1983, Sivakumar Babu & Vasudevan 2008a, 2008b, Das et al. 2009) studied effect of discrete and randomly distributed geofibers (flexible polymeric fibers) on engineering properties of soils through experimental investigations. Previous researchers suggest that silty-sand types of soils are more prone to seepage-induced failure, hence properties of a silty-sand was achieved by mixing 80% locally available fine sand and 20% commercially available kaolin by dry weight and that soil was used as model soil for the present study. The soil used in the present study has sand size particles of 80%, silt size particles of 10% and clay particles of 10%. An average particle size d 50 equals to 0.25mm. According to Unified Soil Classification System (USCS) it is classified as SM type soil. The Maximum Dry unit weight (MDD) and Optimum Moisture Content (OMC) of a soil were found to be 18.75kN/m 3 and 8% according to standard Proctor compaction. The cohesion and angle of internal friction angle of soil compacted at MDD and OMC were found to be equal to 11.6 kpa and 27 and were determined according to direct shear test conducted on saturated soil samples (Das 2009). Polyester fibers were used in the present study. Polyester fibers are commercialized under the brand name Recron 3s. It has a triangular cross section for better anchoring with other ingredients of the mix. Specific gravity of polyester fibers was 1.33 and a tensile strength of 600 MPa. The fibers were found to have 10 denier and an equivalent diameter in the range of µm. The slope model was prepared within a metal strong box having internal dimensions 760 mm 200 mm 410 mm with one side made up of a thick acrylic sheet to observe the slope model during the centrifuge test. The slope model was prepared considering a half portion of an embankment. The prototype dimensions were: height of slope 7.2 m, crest width 7.5 m and inclination of slope 1H: 2V at 30 gravities. The dimensions were so chosen that it will represent an embankment which at just stable condition with a Factor of Safety (FOS) around 1 without any rise in the ground water table for the soil parameters given in Section 2.3. A global failure was observed for an un-reinforced slope at the onset of seepage, as shown in Figure 7a for model ADF2. Failure was observed to initiate with formation of tension cracks at the crest and followed by a typical circular failure surface. In comparison, geofiber reinforced slope with the same boundary conditions, was found to be stable even after subjecting to seepage of 20days, as shown in Figure 7b for model ADF1. Some localized failures were noted to take place near the toe of the slope for model ADF1. Model ADF1 is reinforced with polyester fibers having fiber content f = 0.1% and length of 25 mm. These combinations were decided based on the results reported by Das (2009). Yp (m) Xp (m) Fig. 7(a): Slope Profile after Centrifuge Model Tests for an Un-Reinforced Slope Model ADF2 (in prototype dimensions) Stability analysis of the seepage induced slopes was carried out using limit equilibrium based software package SLOPE/W using ordinary Bishop s method of slices. During stability analysis, the position of phreatic lines was plotted directly from the measured PPT data obtained from the centrifuge model tests (Das 2009). Factor of Safety (FOS) was calculated for each stage of seepage. Initially when the pore water pressure kept on increasing FOS remained constant up to a certain limit. After that it gradually dropped as the pore 951

6 water pressure increased considerably. For an un-reinforced slope ADF2, FOS dropped below 1 at normalized pore water pressure ratio of about In the case of ADF1, FOS started decreasing at pore water pressure ratio 0.36 but it never dropped below 1, as shown in Figure 8. Pore water pressure ratio (u/γh) is the ratio of pore water pressure measured by a PPT placed at half distance from the crest of the slope horizontally from the seepage tank simulator to unit weight times height of the slope. 9 homogeneously mixed Geofiber-Reinforced Soil (GRS) as an alternative fill material. It can be noted that each application was found to have variable optimum combinations of fiber content and fiber length. Preparation of randomly distributed fiber reinforced soils mimics soil stabilization by admixture. Discrete fibers are simply added and mixed with the soil, much like cement, lime, or other additives. However, one of the key issues to be focused for successful implementation of technique in the field is in evolving at a methodology for mixing geofibers with soil. ACKNOWLEDGEMENTS Yp (m) Xp (m) Fig. 7(b): Slope Profile after Centrifuge Model Tests for Fiber-Reinforced Slope Model ADF1 (prototype dimensions) FOS f = 0.1%: l = 25 mm (ADF1) Unreinforced (ADF2) u/γ h Fig. 8: Variation of Factor of Safety with u/γh This indicates that fibers can hold soil particles, restrict their movement and consequently increased the FOS, even at very high pore water pressures. Identical behaviour was observed through physical centrifuge model test. Results of this study indicate that the homogeneously mixed Geofiber Reinforced Soil (GRS) can be an alternative fill material for constructing levees, earthen dams, and other irrigation structures. 3. CONCLUSIONS It can be clearly stated that the geofiber-reinforced soil is a very effective method and which helps to restrain cracking of clay barrier at the onset of differential settlements, to use the expansive soil deposits at the construction sites, and to use The authors would like to thank Master s students Mr B.K. Jha, Mr. Arghya Das and current research scholars Mr S. Rajesh, and Ms Divya Nair for their support and executing tests. Thanks are due to the support extended by the staff at National Geotechnical Centrifuge Facility of Indian Institute of Technology Bombay for their assistance throughout the centrifuge study and thanks are also due to M/s Reliance Industries Limited, Mumbai and M/s TechFab (India), Mumbai for supplying polyester/polypropylene fibers. REFERENCES Ayyar, T.S.R., Krishnaswamy, N.R. and Viswanadham, B.V.S. (1989). Geosynthetics for Foundations on a Swelling Clay, Proceedings of International Workshop on Geotextiles, Bangalore, India, pp Cai, Y., Shi, B., Ng, C.W.W. and Tang, C. (2006). Effect of Polypropylene Fiber and Lime Admixture on Engineering Properties of Clayey Soil, Journal of Engineering Geology, 87(3 4): Das, Arghya (2009). Centrifuge Model Studies on the Behaviour of Geofiber Reinforced Slopes Subjected to Seepage, Masters of Technology Dissertation. Indian Institute of Technology Bombay, Powai, Mumbai, India. Das, Arghya, Jayashree, Ch. and Viswanadham, B.V.S. (2009). Effect of Randomly Distributed Geofibers on the Piping Behaviour of Embankments Constructed with Fly Ash as a Fill Material, Geotextiles and Geomembranes, 27(4): Gray, D.H. and Ohashi, H. (1983). Mechanics of Fiber Reinforcing in Sand, J. Geotech. Engg., ASCE, 109(3): Maher, M.H. and Ho, Y.C. (1994). Mechanical Properties of Kaolinite/Fiber Soil Composite, Journal of Geotechnical Engineering, ASCE, 120(8): Miller, C.J. and Rifai, S. (2004). Fiber Reinforcement for Waste Containment Soil Liners, J. of Environmental Engineering, ASCE, 130(8): Nataraj, M.S. and McManis, K.L. (1997). Strength and Deformation Properties of Soils Reinforced with Fibrillated Fibers, Geosynthetics International, 4(1):

7 Punthutaecha, K., Puppala, A.J., Vanapalli, S.K. and Inyang, H. (2006). Volume Change Behaviours of Expansive Soils Stabilized with Recycled Ashes and Fibers, Journal of Geotechnical and Geoenvironmental Engineering, ASCE, 18(2): Puppala, A. and Musenda, C. (2000). Effects of Fiber Reinforcement on Strength and Volume Change in Expansive Soils, Transportation Research Record, 1736, pp Rodatz, W. and Oltmanns, W. (1997). Permeability and Stress- Strain Behaviour of Fiber-Reinforced Soils for Landfill Liner Systems, Advanced Landfill Liner Systems, H. August, U. Holzlohner and T. Meggyes (Eds.), Thomas Telford (Pubs.), Sivakumar Babu, G.L. and Vasudevan, A.K. (2008a). Seepage Velocity and Piping Resistance of Coir Fiber Mixed Soils, Journal of Irrigation and Drainage Engineering, ASCE, 134(4): Sivakumar Babu, G.L. and Vasudevan, A.K. (2008b). Strength and Stiffness Response of Coir Fiber- Reinforced Tropical Soil, Journal of Materials in Civil Engineering, ASCE, 20(9): Viswanadham, B.V.S., Jha, B.K. and Sengupta, S.S. (2009b). Centrifuge Testing of Fiber Reinforced Soil Liners for Waste Containment Systems, Journal of Practice Periodical of Hazardous, Toxic and Radioactive Waste Management, ASCE, 13(1): Viswanadham, B.V.S., Phanikumar, B.R. and Mukherjee, R.V. (2009a). Swelling Behaviour of a Geofiber-Reinforced Expansive Soil, Geotextiles and Geomembranes, 27(1): Viswanadham, B.V.S., Phanikumar, B.R. and Mukherjee, R.V. (2009c). Effect of Geofiber Reinforcement on Swelling Behavior of an Expansive Soil, Geosynthetics International, 26(5) (In press). Viswanadham, B.V.S., Sengupta, S.S. and Muthukumaran, A.E. (2006). Studies on the Deformation Behaviour of Randomly Reinforced Soil Liners in a Geocentrifuge, Proc. 8 th International Conference on Geosynthetics, 18 22, September 2006, Yokohama, Japan, 4, pp Zhang, Z., Farrag, K. and Morvant, M. (2003). Evaluation of the Effect of Synthetic Fibers and Nonwoven Geotextile Reinforcement on the Stability of Heavy Clay Embankments, FHWA/LA.03/373. Louisiana Transportation Research Center, Baton Rouge, LA, USA, pp Ziegler, S., Leshchinsky, D., Ling, H.I. and Perry, E.B. (1998). Effect of Short Polymeric Fibers on Crack Development in Clays, Soils and Foundations, 38(1):