Experimental Evidences on Thermo-Hydro-Mechanical Coupling in Engineered Clay Barrier for Deep Nuclear Waste Disposal

In the context of using engineered clay barrier in deep nuclear waste disposal, an experimental work was carried out to observe the behavior of compacted swelling clay under thermo-hydro-mechanical (THM) loading. Firstly, the measurement of thermal conductivity has allowed the elaboration of a theoretical model to estimate the thermal conductivity of unsaturated soils. After an evaluation study on the proposed model and three existing models found in the literature, it was concluded that the thermal conductivity of unsaturated soil could be correlated with only one parameter: the air volume fraction. Secondly, the water retention curve, that influences the water transfer in unsaturated soil, was determined at different temperatures. The results showed a decrease of water retention capacity due to heating. A simple model based on the interfacial tension air-water was formulated to simulate this effect. Finally, the soil volume change under complex THM loading was studied. Thermo-mechanical phenomena, which are often observed on saturated clay, were equally observed on the compacted unsaturated clay.