Interface Shear Strengths Between Geosynthetics and Clayey Soils

Interface shear behavior between geosynthetics and clayey soil was investigated by large scale direct shear tests. The interfaces investigated are geomembrane (GM) and clayey soil; GM and geotextile (GT); and GT encased geosynthetics clay liner (GCL) and clayey soil. For GM/clayey soil interfaces, a softer GM resulted in a higher apparent adhesion, and higher water content of the soil yielded lower interface strength. A GM/bentonite interface had a small friction angle of 3 -4 degrees only. For all cases tested, the interface shear strength (tau(f)) was lower than the shear strength of the corresponding soil (tau(fs)), and the lowest tau(f)/tau(fs) ratio was about 0.55. For GM/GT interfaces, the stiffer a GM, the lower the interface shear strength. Also a GT with a woven slit film layer, which is smoother than a randomly aligned nonwoven fiber surface, had a lower interface shear strength. The moisture content of a cover silty soil layer also had a considerable effect on the interface shear strength. Higher water content of the cover soil promoted soil particles entering the openings of the GT and increased the strength. For GCL/clayey soil interfaces, increase the water content of the bentonite in the GCL, reduced the interface friction angle, but increased apparent adhesion. The ratios of tau(f)/tau(fs) was about 0.8-1.0, and it reduced with the increase of the water content of the bentonite and overburden pressure possibly due to migration of water from the GCL to the interface.