This dissertation evaluates the shear behavior of geosynthetic-reinforced soils, representative of a composite element within a GRS wall or slope with specific interest in the shear strength, the volumetric deformation, generation of excess porewater pressure and development of reinforcement tensile force within the reinforced soil. Three series of experiment tests were performed to study the behavior of (1) nonwoven geotextile-reinforced sand under triaxial compression; (2) geogrid-reinforced sand under large-scale plane strain compression; and (3) nonwoven geotextile-reinforced clay under consolidated undrained triaxial compression. Each series of tests offer useful and insightful information for understanding the shear behavior reinforced soils.
In the first part of this dissertation, laboratory triaxial compression tests were conducted to investigate the stress–strain–volumetric responses of geotextile-reinforced sand, featuring the mobilization and distribution of reinforcement strain/loads and soil–geotextile interface shear stress within reinforced soil. A digital image-processing technique was applied to determine residual tensile strain of the reinforcements after tests and then to estimate reinforcement tensile loads. Experimental results indicate that the geotextile reinforcement enhanced peak shear strength and axial strain at failure, and reduced loss of post-peak shear strength. The reinforced specimen had higher shear strength when compared with that of unreinforced soil after deforming by 1–3% of axial strain, which indicates that the geotextile requires a sufficient deformation to mobilize its tensile force to improve the shear strength of reinforced soil. For each reinforcement layer, mobilized tensile strain peaked at the center of the reinforcement and decreased along the radial direction, while the interface shear stress was zero at the center and peaked at a distance of 0.5– 07 reinforcement radius from the center. The mobilized tensile strain of reinforcement increases as confining pressure and number of reinforcement layers increase. This work also demonstrates that the strength difference between reinforced and unreinforced soil was strongly correlated with the sum of maximum mobilized tensile forces of all reinforcement layers, indicating that mobilized tensile force of reinforcements directly improved the shear strength of reinforced soil
In the second part of this dissertation, plane strain tests were conducted to investigate the behavior of geogrid-reinforced sand featuring reinforcement anchorage, which simulates the reinforcement that is anchored by connecting to the facing of retaining walls. Experimental results indicated that the geogrid reinforcement enhanced peak shear strength and axial strain at failure, and reduced loo of post-peak shear strength. Geogrid inclusion also suppressed the volumetric dilation as lateral expansion of reinforced specimens was restrained. Shear strength improvement of anchored specimens increased markedly with the increase of geogrid tensile stiffness while that of non-anchored reinforced specimens appeared to be insensitive to the reinforcement stiffness. An analytical model was proposed based on the concept that additional confinement was induced by reinforcement anchorage, and the verification confirmed that the shear strength difference between anchored specimen and non-anchored specimen was induced by the additional confining pressure from anchoring reinforcement.
In the last part of this dissertation, the shear behavior of nonwoven geotextile reinforced clay was investigated using triaxial compression test under consolidated-undrained condition, with special attention on the generation of excess porewater pressure. Experimental results indicate that nonwoven geotextile as a permeable reinforcement reduces the time of consolidation; however, also induces more volume reduction of reinforced clay specimens. As to the shear strength behavior, the reinforced clay specimens exhibit the improvement on both total and effective shear strength but remain the internal friction angle comparing to pure clay specimens. It is more interesting to observe that higher excess porewater pressure was generated in reinforced clay comparing to that in unreinforced clay. That behavior can be explained by fact that the reinforced clay specimens apparently were more compressed as their lateral deformation restricted by the non-woven geotextile layers. Using the additional confining pressure approach to explain the higher excess porewater pressure behavior of the reinforced clay as the increase of additional confining pressure, the modified porewater pressure parameters, A* and B* were proposed to adopt to reinforced clay specimens. While the A* showed to be independent on the number of reinforcement layers, the value of B* was less than 1 for reinforced clay under saturated condition (instead of B =1 for unreinforced clay) and reducing with the increase of reinforcement layer number. That implies the role of permeable geotextile on increasing the additional confining pressure without generating too much excess porewater pressure.

This dissertation evaluates the shear behavior of geosynthetic-reinforced soils, representative of a composite element within a GRS wall or slope with specific interest in the shear strength, the volumetric deformation, generation of excess porewater pressure and development of reinforcement tensile force within the reinforced soil. Three series of experiment tests were performed to study the behavior of (1) nonwoven geotextile-reinforced sand under triaxial compression; (2) geogrid-reinforced sand under large-scale plane strain compression; and (3) nonwoven geotextile-reinforced clay under consolidated undrained triaxial compression. Each series of tests offer useful and insightful information for understanding the shear behavior reinforced soils.
In the first part of this dissertation, laboratory triaxial compression tests were conducted to investigate the stress–strain–volumetric responses of geotextile-reinforced sand, featuring the mobilization and distribution of reinforcement strain/loads and soil–geotextile interface shear stress within reinforced soil. A digital image-processing technique was applied to determine residual tensile strain of the reinforcements after tests and then to estimate reinforcement tensile loads. Experimental results indicate that the geotextile reinforcement enhanced peak shear strength and axial strain at failure, and reduced loss of post-peak shear strength. The reinforced specimen had higher shear strength when compared with that of unreinforced soil after deforming by 1–3% of axial strain, which indicates that the geotextile requires a sufficient deformation to mobilize its tensile force to improve the shear strength of reinforced soil. For each reinforcement layer, mobilized tensile strain peaked at the center of the reinforcement and decreased along the radial direction, while the interface shear stress was zero at the center and peaked at a distance of 0.5– 07 reinforcement radius from the center. The mobilized tensile strain of reinforcement increases as confining pressure and number of reinforcement layers increase. This work also demonstrates that the strength difference between reinforced and unreinforced soil was strongly correlated with the sum of maximum mobilized tensile forces of all reinforcement layers, indicating that mobilized tensile force of reinforcements directly improved the shear strength of reinforced soil
In the second part of this dissertation, plane strain tests were conducted to investigate the behavior of geogrid-reinforced sand featuring reinforcement anchorage, which simulates the reinforcement that is anchored by connecting to the facing of retaining walls. Experimental results indicated that the geogrid reinforcement enhanced peak shear strength and axial strain at failure, and reduced loo of post-peak shear strength. Geogrid inclusion also suppressed the volumetric dilation as lateral expansion of reinforced specimens was restrained. Shear strength improvement of anchored specimens increased markedly with the increase of geogrid tensile stiffness while that of non-anchored reinforced specimens appeared to be insensitive to the reinforcement stiffness. An analytical model was proposed based on the concept that additional confinement was induced by reinforcement anchorage, and the verification confirmed that the shear strength difference between anchored specimen and non-anchored specimen was induced by the additional confining pressure from anchoring reinforcement.
In the last part of this dissertation, the shear behavior of nonwoven geotextile reinforced clay was investigated using triaxial compression test under consolidated-undrained condition, with special attention on the generation of excess porewater pressure. Experimental results indicate that nonwoven geotextile as a permeable reinforcement reduces the time of consolidation; however, also induces more volume reduction of reinforced clay specimens. As to the shear strength behavior, the reinforced clay specimens exhibit the improvement on both total and effective shear strength but remain the internal friction angle comparing to pure clay specimens. It is more interesting to observe that higher excess porewater pressure was generated in reinforced clay comparing to that in unreinforced clay. That behavior can be explained by fact that the reinforced clay specimens apparently were more compressed as their lateral deformation restricted by the non-woven geotextile layers. Using the additional confining pressure approach to explain the higher excess porewater pressure behavior of the reinforced clay as the increase of additional confining pressure, the modified porewater pressure parameters, A* and B* were proposed to adopt to reinforced clay specimens. While the A* showed to be independent on the number of reinforcement layers, the value of B* was less than 1 for reinforced clay under saturated condition (instead of B =1 for unreinforced clay) and reducing with the increase of reinforcement layer number. That implies the role of permeable geotextile on increasing the additional confining pressure without generating too much excess porewater pressure.

Abdi, M. R., Sadrnejad, A. and Arjomand, M. A., 2009. Strength enhancement of clay by encapsulating geogrids in thin layers of sand. Geotextiles and Geomembranes, 27, (6), 447–455.
Al-Omari, R. R., Al-Dobaissi, H. H., Nazhat, Y. N. and Al-Wadood, B. A., 1989. Shear strength of geomesh reinforced clay. Geotextiles and Geomembranes, 8, (4), 325–336.
AASHTO, 2002. Standard Specifications for Highway Bridges, seventeenth ed. American Association of State Highway and Transportation Officials (AASHTO), Washington, DC, USA.
ASTM D422-63. Standard test method for particle-size analysis of soils. ASTM International, West Conshohocken, PA, USA.
ASTM D4253. Standard Test Methods for Maximum Index Density and Unit Weight of Soils Using a Vibratory Table, ASTM International, West Conshohocken, PA, USA.
ASTM D4254. Standard Test Methods for Minimum Index Density and Unit Weight of Soils and Calculation of Relative Density. ASTM International, West Conshohocken, PA, USA.
ASTM D4595. Standard Test Method for Tensile Properties of Geotextiles by the Wide-Width Strip Method. ASTM International, West Conshohocken, PA, USA.
ASTM D4767-11. Standard test method for consolidated undrained triaxial compression test for cohesive soils. ASTM International, West Conshohocken, PA, USA.
ASTM D5321-12. Standard test method determining the shear strength of soil-geosynthetic and geosynthetic-geosynthetic interfaces by direct shear. ASTM International, West Conshohocken, PA, USA.
ASTM D698–12. Standard test methods for laboratory compaction characteristics of soil using standard effort. ASTM International, West Conshohocken, PA, USA.
Al-Omari, R. R., Al-Dobaissi, H.H., Nazhat, Y.N. and Al-Wadood, B.A., 1989. Shear strength of geomesh reinforced clay. Geotextiles and Geomembranes 8 (4), 325–336.
Athanasopoulos, G. A., 1993. Effect of particle size on the mechanical behaviour of sand–geotextile composites. Geotextile and Geomembranes, 12, (3), 255–273.
Bakeer, R.M., Sayed, M., Cates, P. and Subramanian, R., 1998. Pullout and shear test on geogrid reinforced lightweight aggregate. Geotextiles and Geomembranes 16 (2), 119-133.
Bathurst, R. J. and Karpurapu, R., 1993. Large-scale triaxial compression testing of geocell reinforced granular soils. Geotechnical Testing Journal, ASTM, 16, (3), 293–303.
Bathurst, R.J., Vlachopoulos, N., Walters, D.L., Burgess, P.G., Allen, T.M., 2006. The influence of facing stiffness on the performance of two geosynthetic reinforced soil retaining walls. Canadian Geotechnical Journal 43 (12), 1225-1237.
Boyle, S. R. and Holtz, R. D., 1994. Deformation characteristics of geosynthetics-reinforced soil, 1. Proceedings of the Fifth International Conference on Geotextiles, Geomembranes and Related Products, Singapore, September 1994, pp. 361–364.
Boyle, S. R., 1995. Unit cell tests on reinforced cohesionless soils. Proceedings of Geosynthetics ‘95, IFAI, 3, Nashville, TN, USA, February 1995, pp. 1221–1234.
Broms, B. B., 1977. Triaxial tests with fabric reinforced soil. Proc. Int. Conf. on the Use of Fabrics in Geotechnics, Ecole Nationale des Ponts et Chauss6es, Laboratoire Central des Ponts et Chauss6es, Paris, vol. 3, 129-34.
Casagrande, A., 1936. The determination of the preconsolidation load and its practical significantce. Proc., 1st Intl. Conf. Soil Mech. Found. Eng., p.60.
Chalaturnyk, R.J., Scott, J.D., Chan, D.H.K. and Richards, E.A., 1990. Stresses and deformations in a reinforced soil slope. Canadian Geotechnical Journal 27 (2), 224-232.
Chandrasekaran, B., Broms, B. B. and Wong, K. S., 1989. Strength of fabric reinforced sand under axisymmetric loading. Geotextiles and Geomembranes, 8, (4), 293–310.
Duncan, J. M. and Dunlop, P., 1968. The significance of cap and base restraint. Journal of Soil Mechanics and Foundation, ASCE, 94, (1), 271–290.
Druschel, S.J. and O’Rourke, T.D., 1991. Shear strength of sand-geomembrane interfaces for cover system and lining design, in: Geosynthetics’91 Conference, Atlanta, USA, 159–173.
Elias, V., Christopher, B. R. and Berg, R. R., 2001. Mechanically Stabilized Earth Walls and Reinforced Soil Slopes Design and Construction Guidelines, Report (FHWA-NHI-00-043, National Highway Institute, Federal Highway Administration, Washington, DC, USA.
Fang, Y.S., Chen, T.J., Holtz, R.D. and Lee, W.F., 2004. Reduction of boundary friction in model tests. Geotechnical Testing Journal 27 (1), 3-12.
Farsakh, M. A., Coronel, J. and Tao, M. J., 2007. Effect of soil moisture content and dry density on cohesive soil–geosynthetic interactions using large direct shear tests. Journal of Materials in Civil Engineering, 19, (7), 540–549.
Fabian, K. and Foure, A., 1986. Performance of geotextile-reinforced clay samples in undrained triaxial tests. Geotextiles and Geomembranes, 4, (1), 53–63.
FHWA Federal Highway Administration, 2001a. Mechanically stabilized earth walls and reinforced soil slopes design and construction guidelines. NHI Course No. 132042 (eds. by Elias, V., Christopher, B.R. and Berg, R.R.), Washington DC, USA.
FHWA Federal Highway Administration, 2001b. Performance test for geosynthetic reinforced soil including effects of preloading. Publication No. FHWA-RD-01-118. Washington DC, U.S.
Gray, D. H. and Ohashi, H., 1983. Mechanics of fiber reinforcement in sand. Journal of Geotechnical Engineering, ASCE, 109, (3), 335–353
Gray, D.H. and Al-Refeai, T., 1986. Behavior of fabric vs. fiber reinforced sand. Journal of Geotechnical Engineering, ASCE 112 (8), 804–820.
Haeri, S. M., Noorzad, R. and Oskoorouchi, A. M., 2000. Effect of geotextile reinforcement on the mechanical behavior of sand. Geotextiles and Geomembranes, 18 (6), 385–402.
Hausmann, M. R., 1976. Strength of reinforced soil. Proceedings of the 8th Australasian Road Research Conference, Perth, Australia, Vol. 8, Sect. 13, pp. 1–8.
Hsieh, C. and Hsieh, M.W., 2003. Load plate rigidity and scale effects on the frictional behavior of sand/geomembrane interfaces. Geotextiles and Geomembranes 21 (1), 25-47.
Hou, J., Zhang, M. X., Zhou, H., Javadi, A. A. and Peng, M. Y., 2011. Experiment and analysis of strength behavior of soil reinforced with horizontal-vertical inclusions. Geosynthetics International, 18 (4), 150–158.
Indraratna, B., Satkunaseelan, K.S., Rasul, M.G., 1991. Laboratory properties of a soft marine clay reinforced with woven and nonwoven geotextiles. Geotechnical Testing Journal, ASTM 14 (3), 288–295.
Ingold, T. S., 1980. Reinforced Clay. Thesis, PhD, University of Surrey. U.K.
Ingold, T. S. and Miller, K. S., 1983. Drained axisymmetric loading of reinforced clay. Journal of Geotechnical Engineering, ASCE, 109 (7), 883–898.
Jacobs, F., Ruiken, A. and Ziegler, M., 2012. Experimental investigation of geogrid reinforced soil under plane strain conditions. In: Proc. 5th Asian Regional Conference on Geosynthetics, Bangkok, Thailand, pp. 823-829.
Khedkar, M. S. and Mandal, J. N., 2009. Behaviour of cellular reinforced sand under triaxial loading conditions. Geotechnical and Geological Engineering 27 (5), 645–658.
Kongkitkul, W., Hirakawa, D., Tatsuoka, F. and Kanemaru, T., 2007. Effects of geosynthetic reinforcement type on the strength and stiffness of reinforced sand in plane strain compression. Soils and Foundations 47 (6), 1109-1122.
Kongkitkul, W., Hirakawa, D. and Tatsuoka, F., 2008. Residual deformation of Geosynthetic-reinforced sand in plane strain compression affected by viscous properties of geosynthetic reinforcement. Soils and Foundations, Japanese Society of Soil Mechanics and Foundation Engineering 48 (3), 333-352.
Lackner, C., Bergado, D.T. and Semprich, S., 2013. Prestressed reinforced soil by geosynthetics - Concept and experimental investigations. Geotextiles and Geomembranes 37, 109-123 . doi:10.1016/j.geotexmem.2013.02.002
Latha, G. M. and Murthy, V. S., 2007. Effects of reinforcement form on the behavior of geosynthetic reinforced sand. Geotextiles and Geomembranes, 25 (1), 23–32.
Lee, K.M. and Manjunath, V.R., 2000. Soil-geotextile interface friction by direct shear test. Canadian Geotechnical Journal 37 (1), 238-252.
Leshchinsky, D., Imamoglu, B. and Meehan, C. L., 2010. Exhumed geogrid-reinforced retaining wall. Journal of Geotechnical and Geoenvironmental Engineering, ASCE, 136 (10), 1311–1323.
Liu, C.N., Zornberg, J.G., Chen, T.C., Ho, Y.H., and Lin, B.H., 2009. Behavior of geogrid-sand interface in direct shear mode. Journal of Geotechical and Geoenvironmental Engineering 135 (12), 1863-1871.
Liu, P.Y., 2006. A study of reinforced soil behavior using large-scale plane strain apparatus. Thesis, M.Sc., National Chi Nan University, Nantao, Taiwan.
Long, N. T., Guegan, Y., and Legeay, G., 1972. E ’ tude de la Terre Arme’e a l’appereil Triaxial. Rapport de recherche No. 17, LCPC, Paris, France (in French).
Long, N. T., Legeay, G. and Madani, C., 1983. Soil-reinforcement friction in a triaxial test. Proceedings of the 8th European Conference on Soil Mechanics and Foundation Engineering, Improvement of Ground, Helsinki, Balkema, Rotterdam, the Netherlands, Vol. 1, pp. 381–384.
Michalowski, L.R., 2004. Limit loads on reinforced foundation soils. Journal of Geotechnical and Geoenvironmental Engineering, ASCE 130 (4), 381 -390.
NCMA 2009. Design Manual for Segmental Retaining Walls, 3rd edition, Collin, J., Editor, National Concrete Masonry Association, Herndon, VA, USA.
Nguyen, M.D., Yang, K.H., Lee, S.H., Wu, C.S. and Tsai, M.H., 2013. Behavior of nonwoven geotextile-reinforced soil and mobilization of reinforcement strain under triaxial compression. Geosynthetics International 20 (3), 207-225.
Noorzad, R. and Mirmoradi, S. H., 2010. Laboratory evaluation of the behavior of a geotextile reinforced clay. Geotextiles and Geomembranes, 28 (4), 386–392.
Peng, F.L., Kotake, N., Tatsuoka, F., Hirakawa, D. and Tanaka, T., 2000. Plane strain compression behaviour of geogrid-reinforced sand and its numerical analysis. Soils and Foundations 40 (3), 55-74.
Schlosser, F. and Long, N. T., 1974. Recent results in French research on reinforced earth. Journal of the Construction Division, Proceedings ASCE, 100 (3), 223–237.
Skempton, A. W., 1954. The pore-pressure coefficient A and B. Gétechnique 4 (4), 143-147.
Sridharan, A., Murthy, S., Bindumadhava, B. R. and Revansiddappa, K., 1991. Technique for using fine-grained soil in reinforced earth. Journal of Geotechnical Engineering, ASCE, 117 (8), 1174–1190.
Tafreshi, S. N. M. and Asakereh, A., 2007. Strength evaluation of wet reinforced silty sand by triaxial test. International Journal of Civil Engineering, 5 (4), 274–283.
Tatsuoka, F., Molenkamp, F., Torii, T. and Hino, T., 1984. Behavior of lubrication layers of platens in element tests. Soils and Foundations, Japanese Society of Soil Mechanics and Foundation Engineering 24 (1), 113-128.
Tatsuoka, F. and Haibara, O., 1985. Shear resistance between sand and smooth or lubricated surface, Soils and Foundations. Japanese Society of Soil Mechanics and Foundation Engineering 25 (1), 89-98.
Tatsuoka, F., 1992. Roles of facing rigidity in soil reinforcing. In: Keynote Lecture. Proc. Earth Reinforcement Practice, Fukuoka, Japan, vol. 2, pp. 831-870.
Tatsuoka, F., 2008. Recent practice and research of geosynthetic-reinforced earth structures in Japan. Journal of GeoEngineering 3 (3), 77-100.
Tawfiq, K.S. and Caliendo, J.A., 1993. Laboratory investigation of polyethylene sheeting as a friction reducer in deep foundations. Geotextiles and Geomembranes 12 (8), 739-762.
Tognon, A.R., Rowe, R.K. and Brachman, R.W.I., 1999. Evaluation of side wall friction for a buried pipe testing facility. Geotextiles and Geomembranes 17 (4), 193-212.
Tuna, S.C. and Altun, S., 2012. Mechanical behaviour of sand-geotextile interface. Scientia Iranica 19 (4), 1044–1051.
Unnikrishnan, N., Rajagopal, K. and Krishnaswamy, N. R., 2002. Behaviour of reinforced clay under monotonic and cyclic loading. Geotextiles and Geomembranes, 20 (2), 117–133.
Vidal, H., 1966, “La Terre Armee”, Annales de L’Institute Technique du Batiment et des
Travaux Publics, Vol. 19, No. 223-224, 888-938.
Walters, D. L., Allen, T. M. and Bathurst, R. J., 2002. Conversion of geosynthetic strain to load using reinforcement stiffness. Geosynthetics International, 9 (5–6), 483–523.
Wu, C.S. and Hong, Y.S., 2008. The behavior of a laminated reinforced granular column. Geotextiles and Geomembranes 26 (4), 302–316.
Wu, C. S. and Hong, Y. S., 2009. Laboratory tests on geosynthetics encapsulated sand columns. Geotextiles and Geomembranes, 27 (2), 107–120.
Wu, C. S. and Hong, Y. S., 2008. The behavior of a laminated reinforced granular column. Geotextiles and Geomembranes, 26 (4), 302–316.
Zhang, M. X., Javadi, A. A. and Min, X., 2006. Triaxial tests of sand reinforced with 3D inclusions. Geotextiles and Geomembranes, 24 (4), 201–209.
Zhang, M. X., Zhou, H., Javadi, A. A. and Wang, Z. W., 2008. Experimental and theoretical investigation of strength of soil reinforced with multi-layer horizontal-vertical orthogonal elements. Geotextiles and Geomembranes, 26 (1), 201–209.
Yang, Z., 1972. Strength and deformation characteristics of rienfored sand. Phd.D. Dissertation, UCLA.
Zhang, M.X., Javadi, A.A. and Min, X., 2006. Triaxial tests of sand reinforced with 3D inclusions. Geotextiles and Geomembranes 24 (4), 201–209.
Zhang, M.X., Zhou, H., Javadi, A.A. and Wang, Z.W., 2008. Experimental and theoretical investigation of strength of soil reinforced with multi-layer horizontal-vertical orthogonal elements. Geotextiles and Geomembranes 26(1), 201–209.