Modelling the thermomechanical volume change behaviour of compacted expansive clays

Compacted expansive clays are often considered as a possible buffer material in high-level deep radioactive waste disposals. After the installation of waste canisters, the engineered clay barriers are subjected to thermohydromechanical action in the form of water infiltration from the geological barrier, heat dissipation from the radioactive waste canisters, and stresses generated by clay swelling under almost confined conditions. The aim of the present work is to develop a constitutive model that is able to describe the behaviour of compacted expansive clays under these coupled thermo-hydromechanical actions. The proposed model is based on two existing models: one for the hydromechanical behaviour of compacted expansive clays and another for the thermomechanical behaviour of saturated clays. The elaborated model has been validated using thermo-hydromechanical test results on compacted MX80 bentonite. Comparison between the model prediction and the experimental data shows that this model is able to reproduce the main features of volume changes: heating at constant suction and pressure induces either expansion or contraction; the mean yield stress changes with variations of suction or temperature.