Interface shear strength of geosynthetics: Evaluation and analysis of inclined plane tests

The inclined plane test (IPT) is commonly performed to measure the interface shear strength between different materials as those used in cover systems of landfills. The test, when interpreted according to European test Standards provides the static interface friction angle, usually assumed for 50 mm displacement and denoted as ϕ50stat. However, if interpreted considering the several phases of the sliding process, the test is capable of yielding more realistic information about the interface shear strength such as differentiating interfaces which exhibit the same value of ϕ50stat but different behavior for displacement less than 50 mm. In this paper, the IPT is used to evaluate the interface shear strength of some materials usually present in cover liner systems of landfill. The results of the tests were analyzed for both, the static and the dynamic phases of the sliding and were interpreted based on the static initial friction angle, ϕ0, and the limit friction angle, ϕlim. It is shown that depending on the sliding behavior of the interfaces, ϕ50stat, which is usually adopted as the designing parameter in stability analysis, can be larger than ϕ0 and ϕlim.