Transient temperature and water distributions in unconstrained compacted granular bentonite under elevated temperatures

This paper focuses on understanding transient temperature and water redistributions in compacted bentonite under thermal gradients in high-level nuclear waste disposal repository, particularly during the initial drying of granular bentonite with localized water content and volume changes near the canister. One-dimensional heating tests were conducted to investigate the coupled thermo-hydro-mechanical response of compacted granular MX80 bentonite layers under unconstrained and globally constant water content conditions during basal heating, encompassing both prolonged heating processes followed by natural cooling. Measurements of the transient temperature and volumetric water content redistributions at different vertical distances from the basal heating plate under high-temperature gradients and the global volumetric strains reveal varying rates of heat transfer and water vapor diffusion processes and associated volume change. A hysteretic relationship between volumetric water content and soil temperature during heating and cooling was found to be linked to soil water retention mechanisms. Temperature and water content relationships with local axial strains were found to be useful in evaluating density gradient changes that may occur near the canister.