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, a LLDPE or HDPE smooth geomembrane, and overlying potash salt. The subgrade soil was gravelly sand with 25 percent gravel content. Failure occurred at the geomembrane/soil interface for each shear test. Cyclic loading data indicated 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.
This note presents the results of a cyclic shear test of a secondary containment liner system composed of sand/GCL/sand. The GCL was a needle-punch-reinforced woven/nonwoven product with a thin geomembrane laminated to the nonwoven side. Under a normal stress of 100 kPa, shearing occurred at the sand/geomembrane interface and the GCL sustained no visible damage after 25 cycles of loading with a displacement amplitude of 20 mm and a frequency of 1 Hz. Material property tests performed on pre-cyclic and post-cyclic GCL samples provided additional evidence that the GCL specimen did not sustain damage due to cyclic loading. Analysis of the cyclic loading data indicates hysteretic stress-displacement behavior that is broadly similar to natural soils and displays strength and stiffness degradation as well as reduction in damping ratio with continued cycling.
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