Study on modelling of compacted bentonite under wetting and drying cycles

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Bentonite used in the engineered barrier of nuclear waste disposal facilities will swell on wetting and undergoes drying caused by heat from the waste. Therefore, analyses of the engineered barrier are required to reproduce volume change with the change in saturation. In general, a hydro-mechanical coupled analysis is required taking into account the water retention properties of the soil when considering volume change with saturation. However, the soil-water characteristic properties are dependent on soil classification, dry density, etc., and relevant soil-water characteristic properties of the target materials (bentonite/silica sand of 70:30, dry density of 1.6Mg/m3) have not previously been obtained. Additionally, void ratio-suction relationships for the bentonite materials have not been elucidated. In this study, the material and soil-water characteristic properties for volume change with change in saturation have been obtained from column tests for the compacted bentonite/sand mixture. In particular, the changes in suction and void ratio during drying and wetting processes showed that bentonite without saturation history changed reversibly, and bentonite with saturation history changed irreversibly. Reproduction analysis of the controlled-suction column tests by the vapour equilibrium technique was performed using the obtained parameters to validate the modelling method.

9th International Congress on Environmental Geotechnics (ICEG2023)

Engineered Barriers