Heat and moisture migration in a geomembrane-GCL composite liner subjected to high temperatures and low vertical stresses

This paper presents the results of an experimental and numerical modelling of heat and moisture migration conducted on a composite liner comprised of a geomembrane (GMB) and a geosynthetic clay liner (GCL), over a compacted subgrade and subjected to prolonged elevated temperatures at low overburden stresses typical of brine storage ponds or solar evaporation ponds. Results are presented for a GMB sitting on a fully hydrated GCL. Heating the top of the composite liner caused a measurable increase in subgrade temperature to at least to 250 mm below the GCL. However, the presence of an air gap, simulating the presence of a wrinkle in the geomembrane, at the interface between the GMB and the GCL reduced the impact of the high temperatures on the subgrade temperature profile with depth. The change in temperature profile was accompanied by moisture migration from the GCL to the subgrade material. However no desiccation cracks were observed in the GCL and the bentonite was still in a gel form at the end of the time period investigated. Numerical modelling using finite element method (FEM) was performed to simulate the results obtained experimentally. It was found to predict accurately the temperature changes that have occurred in the subgrade material and moisture changes that occurred in both the GCL and subgrade materials.