Evaluation of Prototype Geosynthetic Clay Liners in Landfill Cover Applications

Geosynthetic clay liners (GCLs) are factory manufactured barriers, typically consisting of sodium bentonite clay between two geotextiles. Because of their low hydraulic conductivity, GCLs are frequently used as a replacement for regulatory prescribed compacted clay liners. With their many benefits, GCLs have their limits. Several field studies have assessed the in-service performance of GCLs in landfill covers. In some cases, GCLs exhibited high in-service hydraulic conductivities as compared to initial preconstruction laboratory results. Past research has demonstrated that GCLs which undergo both wetting and drying cycles combined with cation exchange can experience increases in hydraulic conductivity over time. To prevent this, the current industry standard is to either test the adjacent soil for chemistry to evaluate compatibility, or to install an overlying synthetic membrane to prevent clay desiccation. This study exposed prototype polymer-modified GCLs to several wetting and drying cycles in a calcium solution, representative of aggressive landfill cover conditions. GCL samples were then tested for hydraulic performance, and results were compared to traditional GCLs that underwent the same conditions. This study demonstrated that certain polymer-modified GCLs can be a solution to offset the effects of desiccation and cation exchange.