Geomembrane damage due to static and cyclic shearing over compacted gravelly sand

Several large-scale laboratory tests were conducted on multi-interface geomembrane liner specimens to assess damage effects from static pressure, cyclic loading, and large-displacement static shear. The specimens consisted of compacted subgrade soil, an LLDPE or HDPE smooth geomembrane, and overlying potash salt. The subgrade soil was gravelly sand with 25% gravel content. Failure occurred at the geomembrane/soil interface for each shear test. Cyclic loading data indicated that the LLDPE geomembrane had slightly lower values of interface shear stiffness and damping ratio than the HDPE geomembrane. Shear stiffness was essentially constant and damping ratio decreased with continued cycling for both geomembranes. Geomembrane damage for the static pressure and cyclic loading tests consisted of minor to moderate dimpling, with no holes created. Damage was considerably more severe for the large-displacement shear tests, and consisted of deep scratching and gouging of the geomembranes. Two holes were created in the LLDPE specimen and no holes were created in the HDPE specimen as a result of shear displacement. The findings indicate that severe geomembrane damage can result from shear displacement against a compacted subgrade soil with gravel. Considering that shear displacements commonly occur within landfill liner systems due to such mechanisms as waste settlement, the findings suggest that additional research is needed on expected levels of shear-induced damage for geomembranes placed adjacent to soil layers with coarse particles, including compacted clay liners containing gravel.