Compaction Moisture Effect on Geomembrane/Clay Interface Shear Strength

Results of 72 UU and CU direct shear tests on kaolin clay interfaces with two geosynthetic materials are presented. Tested are conducted using smooth High Density Polyethylene (HDPE) and textured HDPE geomembranes. Each interface is tested under four normal stresses: 25, 100, 250, and 500 kPa. The effects of compaction moisture content and pre-shear compression/consolidation conditions on the interface properties are investigated. A discussion on fundamental aspects related to interface shear strength and efficiency is presented. Results indicated that an increase in the clay compaction moisture content leads to a decrease in the shear strength of the sheared as-compacted interfaces. The overall efficiency of the clay/textured HDPE interface is approximately 1 when tested under UU condition, indicating that failure plane is passing through the clay particles. Under CU condition, the pre-shearing compression/consolidation process allowed interlocking between the clay particles and the geomembrane's texturing. Such interlocking yielded an interface efficiency higher than 1 (interface efficiency is defined as the ratio of the interface shear strength to the clay shear strength at the same testing conditions.) In CU tests, and for saturated and wet of optimum compacted kaolin/ textured HDPE, an increase in the shear strength of the interface and in the overall efficiency is estimated due to an increase in the length of the failure path along which shearing takes place.