Numerical Investigation of Drying of a Geosynthetic Clay Liner in a Composite Liner System Subjected to High Temperatures

摘要

Coal seam gas (CSG) wells produce large amounts of brines which are disposed in ponds lined mostly with composite liners consist of geomembrane (GMB) and geosynthetic clay liner (GCL). Some estimates suggest that these liners can be exposed continuously to temperatures close to 70ºC-80ºC due to the combined effect of solar radiation and brine processing. One potential consequence of the presence of elevated temperatures is the development of thermal gradients across the liner towards the cooler subgrade soil. The presence of a thermal gradient can create a risk of outward moisture movement and possible desiccation of the GCL. The situation is exacerbated by the presence of an overlying GMB preventing rehydration of the GCL with moisture from above. This study investigates the drying process of GCL pre-hydrated to 50% degree of saturation when subjected to elevated temperatures. A finite element model was used to study the heat and the mass movement through the GCL and the underlying subgrade. It has been found that less hydrated GCLs are more prone to drying and desiccation cracking. Long term extreme heating can also affect fully hydrated GCLs if the brine ponds are exposed to solar radiation for longer periods of time. This paper highlights the importance of careful planning of the operation of the ponds to allow full hydration of the GCL to take place.