Interface shear damage to a HDPE geomembrane. I: Gravelly compacted clay liner

An experimental program of large-scale direct shear tests has indicated that shear displacement of a high-density polyethylene (HDPE) geomembrane (GM) over a gravelly compacted clay liner (CCL) under moderate to high normal stress conditions can cause much greater damage to the geomembrane than static pressure alone. Essentially, no damage was observed at low normal stress. The greatest geomembrane damage occurred at high normal stress (1,658 kPa) and yielded an average of 169 holes/m², with a maximum hole size of 23 Size, angularity, and hardness of the gravel particles are also important factors with regard to potential damage. Geomembrane damage was greatly reduced when a needle-punched geosynthetic clay liner (GCL) was placed between the geomembrane and gravelly CCL, including one test conducted at very high normal stress (4,145 kPa). The findings suggest that gravelly soils should be viewed with caution for the construction of GM/CCL composite liners for landfill bottom liner systems and other moderate- to high-stress applications. If there is a reasonable expectation for GM/CCL interface shear displacement, project-specific direct shear tests should be conducted to determine the potential for shear-induced geomembrane damage. Recommendations are provided for the performance of such tests and for design options when damage mitigation is necessary.