Thermo-Hydro-Mechanical Column Test on Compacted Bentonite Buffer: Experimental Setup Development and Preliminary Results

Compacted smectite clays/bentonites are being used as buffer material in deep geological repository (DGR) considered as suitable solution for isolating high level radioactive waste. In the DGR, the compacted smectite clay undergoes coupled thermal, hydraulic, and mechanical (THM) loading conditions. This paper presents a state-of-the art experimental setup developed to study THM behavior of buffer material and preliminary results obtained from THM experiment. The equipment was designed at IIT Patna and commissioned by HEICO Ltd. Various sensors were attached to cylindrical soil sample (15 × 10 cm) to find out change in various properties such as soil moisture tension, temperature and swelling pressure at pre-selected locations with time. All these sensors were connected to the data logger for monitoring the results. Thermal and thermo-hydraulic tests were conducted in two stages. In the first stage, temperature was applied with gradual increment up to 90 ℃ from bottom of soil sample. In the second stage, after attaining the uniform temperature at particular depths, water was supplied from top of soil sample. In the first stage of the experiment, test results showed that the temperature at various locations equilibrated within about 14 h, thereafter, no significant variation in temperature was noted. Swelling pressure showed an increasing trend during the coupled thermal and hydraulic loadings. In accordance with experimental findings, THM behavior of smectite clays, which serve as a buffer material in deep geological repositories, can be assessed using reliable data from a newly developed column device.