Water retention characteristics of unsaturated bentonite–sand mixtures under controlled-temperature

Unsaturated bentonite–sand mixtures (BSMs) are accepted generally as ideal buffer/backfill materials in geologic repositories because of its excellent performance. Water retention characteristics are the important factor that affect the engineering properties of BSMs, but little attention has been devoted to that of Gaomiaozi (GMZ) BSMs under controlled-temperature in high suction range. This study evaluated the soil–water characteristic curves (SWCCs) of compacted GMZ BSMs using the vapour equilibrium technique with different sand content and temperature under unconfined conditions. It was found that the sand grains size had a negligible effect on the SWCCs in the high suction range. As the temperature increased, the decreasing adsorption and the increasing evaporation capacity promoted the decrease of water content. The BSMs changed from the compact structure to a loose structure with increasing sand content, which strengthened the flow of vapour and evaporation of water from bentonite and leaded to an observable reduction of water retention characteristics of GMZ BSMs. We presented a new empirical equation for unsaturated BSMs in the high suction rang considering effects of temperature and sand content, and that processed the data more efficiently and described satisfactorily the effects of temperature and sand content on the SWCCs of GMZ BSMs.