Investigation of soil-water characteristic curves for compacted bentonite considering dry density

Deep geological repositories are often considered for the disposal of high-level radioactive wastes (HLW). HLW should be disposed of safely and permanently using two barrier systems: engineered barrier systems (EBS) and natural barrier systems (NBS). An EBS is an artificial concept comprising various components. A buffer is one of the most important components because it plays a crucial role in the safety of the entire disposal system, and compacted bentonite is considered a highly adequate buffer candidate material. The compacted bentonite is located between a canister with HLW packages and rock-mass. In compacted bentonite, the dry density varies in actual repository environments, and it may be necessary to consider this when evaluating the disposal system safety. As groundwater flows into the rock mass and buffer, the degree of saturation of compacted bentonite increases, with the saturation behavior represented by a soil-water characteristic curve (SWCC). In this study, SWCC tests of Korean compacted bentonites were conducted based on the chilled-mirror dew point temperature condensation (CMDPTC) method, incorporating the dry density variation. The van Genuchten fitting parameters (alpha, n) were obtained; alpha decreased exponentially, and n increased linearly according to the dry density. Furthermore, using the obtained SWCC datasets, a simple empirical model was proposed to estimate the van Genuchten fitting parameters.