SHEAR BEHAVIOR OF AN UNREINFORCED GEOSYNTHETIC CLAY LINER

Dry and hydrated specimens of an unreinforced geomembrane-backed geosy nthetic clay liner (GCL) were sheared against a textured geomembrane u sing a torsional ring shear apparatus to study the shear behavior of g eomembrane encapsulated bentonite. Shearing of the dry GCL against a t extured geomembrane at high normal stresses resulted in failure occurr ing within the GCL adhesive that attaches the bentonite to the geomemb rane backing and not the GCL bentonite/geomembrane interface. This typ e of failure occurred when both smooth and textured geomembranes were used as the GCL backing material. Conversely, shearing of the hydrated GCL against a textured geomembrane resulted in failure occurring at t he GCL bentonite/textured geomembrane interface. The order of hydratio n and normal stress application was found to significantly affect the GCL/textured geomembrane interface shear strength. The mobilized shear strength of the GCL/textured geomembrane interface does not equal the drained shear strength of bentonite because of the effect of geomembr ane texturing and the lack of drainage during dry and hydrated GCL tes ting, respectively. Finally, the hydrated GCL/textured geomembrane int erface exhibits an increase in peak shear strength of approximately 13 % per log cycle of the shear rate. Therefore, the selection of a shear displacement rate is important for unreinforced geomembrane-backed GC L/textured geomembrane interface shear tests.