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The leachate collection system and the double liner required by the EPA for solid and hazardous waste landfills consist typically of a combination of geosynthetics materials and natural or processed soils. This research is conducted to study the load-deformation behavior of a multi layered landfill liner system under stresses imposed by the waste fill. Experimental and analytical work achieved in this research is summarized as follows: (1) Experimental Evaluation of the shear stress-shear deformation characteristics of seven geosynthetic interfaces encountered in landfill lining systems in addition to four geosynthetic materials and three soils. The investigated materials included: Ottawa sand, kaoline clay, and limestone gravel. These soils represent the clay liner, drainage material, and cover soil, respectively, in a landfill. The four geosynthetics included: smooth and textured HDPE geomembrane, Polypropylene nonwoven geotextiles, and solid rib extruded geonet. (2) Development of two constitutive models for the shear stress-shear deformation behavior of the tested interfaces. Parameters of both models are obtained for all interfaces tested in the experimental work. The effect of degree of saturation and compacted soil structure on these parameters is also evaluated and implemented in the model. Furthermore, verification of the two models was achieved. (3) Finite Element (FE) simulation of the load-deformation behavior of a liner system over a trough subsidence. The FE simulations included a study of the effect of subsidence on the mobilized interface shear resistance and associated shear deformations and strains.