Estimating effective thermal conductivity of unsaturated bentonites with consideration of coupled thermo-hydro-mechanical effects

The thermal conductivity of compacted bentonites is one of the key properties for performance assessment in design of the engineered barrier systems. This study presented an effective thermal conductivity model for compacted bentonites with a consideration of the coupled thermo-hydro-mechanical (THM) phenomena involved in the barrier systems. The model was developed based on the structural connections of pores and the solid phase and the series-parallel arrangements of multiphase fluids (water and air-vapor mixture) in the pore system, and was represented as a function of porosity, the degree of saturation, temperature, and pressures of the fluid phases. The proposed model was comprehensively verified by five sets of laboratory data on the MX-80, FEBEX, Kunigel-V1 and GMZ01 compacted bentonite materials with different dry densities, water content and mineralogical composition, and good agreements were obtained between the model predictions and the laboratory measurements. It is demonstrated that the model predictions strictly fall within the Wiener bounds, and mostly obey the Hashin-Shtrikman bounds over wide ranges of porosity and saturation.