Experimental study on thermo-hydro-mechanical behaviour of compacted kaolin clay

Abstract

Several engineering problems are associated with unsaturated soils that are subjected to high temperature due to the environments where they are located or activities around them. Typical examples include upper layers of soils in tropical regions, soils around geothermal structures, landfill liners and clay barriers around nuclear waste repository systems. Previous researchers have reported that variations in stress, suction and temperature affect the mechanical behaviour of unsaturated soils. Notwithstanding already existing studies, the influence of temperature on some unsaturated soils is still a challenge relative to saturated soils, as the results from these existing studies are soil specific and cannot be inferred as the behaviour of all unsaturated soils. A sound understanding of the behaviour of unsaturated kaolin clay without a hydraulic history under temperature and suction variation is still required. The main objective of this study was to investigate the influence of temperature variations on the volumetric and water retention behaviours of statically compacted kaolin clay. Statically compacted samples at a dry side of optimum were tested at different temperatures, using standard and suction controlled oedometer cells, to investigate the influence of temperature on volumetric behaviours. The tests were carried out considering various stress paths. Additionally, pressure plate and vapour equilibrium tests were carried out following a drying path at two temperatures and void ratios to investigate the influence of temperature and densities on the water retention of statically compacted kaolin clay. Complimentary tests were carried out to investigate the effect of temperature variation on overall volume and suction, through the filter paper method. Either collapse or expansion occurred on wetting, depending on the density of the sample. Compressibility was found to increase with an increase in temperature. For tests at constant suction, increase in temperature was found to increase compressibility at low suction, but compressibility was unaffected by temperature at high suction. The results when presented in the light of LC model, indicated a shift of the LC curve to the left at high temperature. The study demonstrated that temperature variation alone was sufficient to vary suction and volume. Features captured on other soils were also identified; for example, yield stress was found to increase with suction. Water retention was observed to decrease with an increase in temperature and increase with void ratio (along the capillary fringe). Good fits were observed, when pertinent soil water retention models were fitted to the obtained water retention data. The study noted that the hydro-mechanical behaviour of a sample prepared at the wet of optimum water content is significantly different from dry of optimum sample and this should be considered when predicting soil behaviour. The study also demonstrated that increase in temperature will affect samples without hydraulic history differently. Further work is still required on an extended range of temperature and suction.