Water exchange across a subgrade-GCL interface as impacted by polymers and environmental conditions

This paper examines the hydration behaviour of polymer enhanced geosynthetic clay liners (GCLs) under both isothermal conditions and diurnal cyclical temperatures as recorded at a Melbourne landfill site. The diurnal temperature cycles introduced thermal gradients, which induced water movement downwards into the subgrade. It was found that the bulk of the thermal and hydraulic effects occurred within the upper 50 mm of the subgrade layer. Compared to isothermal conditions, diurnal temperature cycling's main effect was to suppress GCL hydration. Thermal gradients induced capillary breaks, and GCL hydration was thus limited to vapour phase hydration from the subgrade, which restricted the gravimetric water content of the GCLs to <30%. The hydration process at the interface was observed to gradually return to isothermal condition hydration levels once the temperature cycle conditions were removed. While the polymer's presence ensures the adsorption of more water, it also renders GCLs more sensitive to the effects of temperature. This study provides insights on the hydration behaviour of uncovered GCLs in field applications and the impact that diurnal temperature cycles can have on GCL hydration in a Mediterranean type climate.