Thermo-Hydro-Mechanical Behaviour of Composite Geosynthetic Lining Systems under High Temperature and Low Pressure

Abstract

Aim. Composite geosynthetic clay lining systems (CGCLS), a combination of high density polyethylene geomembranes and geosynthetic clay liners (GCLs), have been used in brine ponds to manage the large amount of waste water produced by coal seam gas extraction. Exposure to sunlight combined with the thermal properties of brine water can lead to temperatures of up to 85-95°C at the liner. The goal of the thesis is to investigate whether GCLs may desiccate in engineering applications with high temperatures and low overburden loads. Methodology. A multi-phase, thermo-hydro-elastic theory of soil behaviour is first adopted to the study of desiccation of GCLs. The theory has been implemented in a computer simulation environment (CODE_BRIGHT). Next, the dependence of the GCL’s soil-water chararcteristic curve (SWCC) on temperature and overburden load are characterised experimentally and new forms of the SWCC equations are developed. A set of column studies are conducted. The aims of the column studies are to assess whether desiccation of bentonite occurs and to generate experimental data that can be used to validate the above-mentioned theory. Findings. The new developed SWCCs perform well in predicting the effects of void ratio on SWCC based on the available data. A non-linear thermo-hydro-elastic theory is found to be capable of replicating the observed change in time of temperature and water contents in the subsoil with reasonable accuracy, even with minimal back-fitting of data and independent determination of material properties of both GCLs and subsoil. The thesis has established experimentally, for the first time, that GCLs in composite liners, subject to surface temperatures of 78°C and overburden loads of 20kPa, may experience high levels of desiccation cracking. The findings of this thesis call for caution in using the type of GCL studied here in applications in which they are exposed to temperatures higher than 60°C.