Abstract
A combination of high-density polyethylene (HDPE) geomembranes (GMs) and geosynthetic clay liners (GCLs), is widely used for protecting groundwater from contaminated water in landfill liners and brine ponds. While a low-permeability and chemically-resistant GM prevents downward flow of water, the GCL acts as a diffusive and advective buffer against the flow under defects in the GM. However, it has been shown that GCLs may desiccate due to thermal gradients. Downward flow of water vapour from the GCL towards cooler areas near the aquifer is the main mechanism expected to control the water content of GCL. Defects in the GM are clearly undesirable because they can lead to contaminant migration though the liner. On the other hand, defects may also allow water to rehydrate the GCL. Little is known, however, about this potential for rehydration. In this study, we validate a thermo-hydro-mechanical model of composite liner systems, based on computer software CODE_BRIGHT, and use it to simulate hydration-dehydration dynamics of composite GCLs in a landfill liner. Specifically, we assess the extent to which downward water flow through a defect can counteract desiccation. We find that close to the defect, stresses in the bentonite remain compressive and the likelihood of desiccation is thus reduced. However, under the low transmissivity conditions encountered for GCLs, the effect seems localised and disappears away from the defects.
