Modelling of thermally induced desiccation of geosynthetic clay liners

Composite basal liners for municipal solid waste landfills may be comprised of geosynthetic materials such as geomembranes and geosynthetic clay liners. Exothermic degradation of organic matter or hydration of incinerator ash within the landfill generates heat within the waste mass. This creates thermal gradients through the composite liner, which have the potential to induce a net movement of moisture away from the warmer liner. The result is a potential for desiccation that may impair the long-term performance of the GCL. This paper presents the results of an investigation into the potential for desiccation of GCLs under thermal gradients using the numerical model SUMMIT. The results from a series of large-scale laboratory experiments are compared with predictions made using the numerical model in terms of volumetric water content and temperature distributions. The influence of key thermal and hydraulic parameters is discussed, as well as the ability of the model to predict situations where cracking is likely. Key limitations of the model, especially the assumption of a rigid media, are identified and discussed within the context of GCL desiccation behaviour. It is concluded that although the SUMMIT model may be suitable for general investigations of thermally induced moisture movement, a more comprehensive model is required to extend the investigation to the case of GCLs as part of a composite lining system.