Transient and hysteretic thermo-hydraulic response of constrained bentonite under high temperature

There is an important need for validation data for long-term simulations of bentonite buffers used in geological repositories for high-level radioactive waste. To meet this need, an instrumented tank-scale heating-hydration test on compacted MX80 bentonite ( D = 554.5 mm; h = 206 mm) with a duration longer than 2 years was conducted with central outward heating followed by circumferential inward hydration under constrained conditions. The transient thermally-induced drying process was dominated by water phase change and vapor diffusion in the granular bentonite away from the heater, while the transient hydraulic process was found to be dominated by suction-driven liquid flow toward the heater. Despite the long test duration, the bentonite retained largely unsaturated conditions under low-pressure water infiltration. The transient measurements during heating and hydration were found to be useful in evaluating a coupled set of thermo-hydraulic relationships, including a nonisothermal soil-water retention curve, a new hydraulic conductivity function and a thermal conductivity function.