UC San Diego

Liner systems are used in a wide array of applications to prevent the spread of contaminants into the environment. These liner systems have two main components: a geomembrane (GM) and a compacted clay liner (CCL). GMs are susceptible to damage both during installation and the service life of the liner system. The most common source of damage is puncture due to granular material (e.g., gravel or stones) in direct contact with the GM resulting in the formation of a hole in the liner. While multiple studies have investigated puncture due to a granular layer above the GM, puncture due to granular material in the subgrade below has not received comparable attention. A series of tests were performed using a large-scale direct shear machine to investigate possible damage to a high density polyethylene (HDPE) GM due to interface shearing over a gravelly CCL for a wide range of normal stress levels. Results indicate that shear displacement of a HDPE GM over a gravelly CCL can significantly increase GM damage compared to static pressure alone. Damage increased with increasing normal stress. Essentially no damage was observed at the lowest normal stress (72 kPa), while severe damage was observed at high normal stress (1658 kPa). Placement of a hydrated nonwoven/nonwoven (NW/NW) needle-punched (NP) geosynthetic clay liner (GCL) between a GM and gravelly CCL was shown to dramatically reduce GM damage, including one test conducted at very high normal stress (4145 kPa)