Evaluation of the water retention curve for geosynthetic clay liners

Geosynthetic clay liners (GCLs) are frequently used as part of composite base liners for landfills. Heat generated by the waste can potentially cause drying of the hydrated GCL. In order to better understand the performance of GCLs under such conditions, an assessment of the water retention characteristics under drying conditions is required. To date, such an investigation has not been undertaken for GCLs, although some data exists for compacted bentonite. This paper presents the results of laboratory testing aimed at obtaining water retention curves (WRCs) for two GCL materials representative of those commonly used in practise. Pressure plate and pressure membrane extractors were used to assess the relationship between the degree of saturation and the applied capillary pressure (suction) for a range of capillary pressures between 10 and 10 000 kPa. The effect of overburden pressure was investigated, as was the relationship between capillary pressure and bulk GCL void ratio. Volume change behaviour was found to have a significant effect on the WRCs. Representative parameters were obtained by fitting the predictions of three WRC models to the experimental data. Reasonable fits were achieved and the parameters obtained may be used for numerical modelling.