Shear-induced geomembrane damage due to gravel in underlying compacted clay

Lining systems for landfills and heap leach pads are often constructed with compacted clay liners (CCLs) containing significant amounts of gravel. Geomembranes placed against gravelly CCLs are vulnerable to damage due tohighoverburden stress andinterface shear displacement. This invited paper reports results from the first experimental investigation of shear-induced damage to geomembranes placed in contact with gravelly compacted clay. A series of large-scale direct shear tests was conducted for the interface between smoothHDPE geomembranes and CCLs with 20 percent gravel. The tests were performed for normal stress levels ranging from 72 to 1658 kPa to simulate overburden stresses associated with bottom liner systems. Replicate interface shear tests were also performed for normal stresses up to 4145 kPa with a geosynthetic clay liner (GCL) placed in between the geomembrane and the CCL to evaluate protection provided by the GCL. Results indicate that shear displacement between a geomembrane and a gravelly CCL under high normal stress conditions can cause severe damage to the geomembrane. The testing program also found that placing a GCL between a geomembrane and a gravellyCCL can essentially eliminate such damage.