Direct shear and tipping board tests were performed to evaluate the shear resistance of interfaces between various geosynthetics and between geosynthetic and soil. The geosynthetic materials were candidates of the model liner system for the study of the 1988 Kettleman landfill slope failure. Modifications of test apparatus and procedure were made in consideration of the sheeting-like liner materials and the low stress state(< 5kPa) of the models. In order to avoid erroneous reading due to roller friction, the conventional direct shear box was modified such that the shear resistance of liner interface was measured at the upper plate of shear box. Various potential factors had been considered and their effects on the interface shear resistance were investigated. It was found that the shear resistance of geosynthetic liner interface was very sensitive to the surface cleanliness. The increase in surcharge loading time could significantly increase the interface shear resistance. Due to prolonged or multiple shearing, the polished geosynthetic surface reduced both peak and "residual" interface shear strengths. However, this effect tends to decrease and become insignificant at a greater shear distance (e.g., 25-50cm). Temperature apparently had an effect on the interface shear resistance when the temperature was low (e.g. < 20°C). Results of the study provided an experimental basis for estimating the interface shear resistance of the model liner system. The study also demonstrated the direct shear and tipping board apparatus discussed herein provided effective tools for evaluation of the interface shear resistance under low stress conditions.
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