Resilience of Australian polymer-modified powdered sodium bentonite geosynthetic clay liners to downslope bentonite erosion

Loss of bentonite from geosynthetic clay liners (GCLs), installed as a component of a composite liner beneath an exposed geomembrane (GM) on the side-slopes of landfills and exposed to thermal cycling, has become a topic of some importance recently as it raises questions on the long-term durability of modern landfill lining products. Laboratory drip testing was used to evaluate the resilience of four GCLs containing polymer-modified powdered bentonite against down-slope bentonite erosion. Onset erosion features were observed only after 60–140 drip cycles. In all probability the polymer-modified bentonite can be expected to self-heal if no further erosion takes place at these initial stages. A detailed assessment of the drip test and comparison with known field test results, indicates that the drip rate and duration of the laboratory test conducted at ≈22 °C is equivalent to in-field conditions where daytime temperatures of the GM/GCL may reach 65 to 75 °C. Thus, meaningful accelerated testing of polymer-modified powdered bentonite GCL products is possible. The results need to be validated with in-field tests under local conditions because recoverable service-lives of GCL products ultimately depend on the in-field conditions where these materials are deployed.