The compacted bentonite buffer is a key component of the engineered barrier system in deep geological repositories for high-level radioactive waste disposal. Groundwater infiltration into the deep geological repository leads to the saturation of the bentonite buffer. Bentonite saturation results in bentonite swelling, gelation and intrusion into the nearby rock discontinuities within the excavation damaged zone of the adjacent rock mass. Groundwater flow can result in the erosion and transport of bentonite colloids, resulting in bentonite mass loss which can negatively impact the long-term integrity and safety of the overall engineered barrier system. The hydro -mechanicalchemical interactions between the buffer, surrounding host rock and groundwater influence the erosion characteristics of the bentonite buffer. Hence, assessing the critical hydro-mechanicalchemical factors that negatively affect bentonite erosion is crucial for the safety design of the deep geological repository. In this study, the effects of initial bentonite density, aperture, discontinuity angle and groundwater chemistry on the erosion characteristics of Bentonil WRK are investigated via bentonite extrusion and artificial fracture experiments. Both experiments examine bentonite swelling and intrusion into simulated rock discontinuities; cylindrical holes for bentonite extrusion experiments and plane surfaces for artificial fracture experiments. Compacted bentonite blocks and bentonite pellets are manufactured using a compaction press and granulation compactor respectively and installed in the transparent extrusion cells and artificial fracture cells. The reference test condition is set to be 1.6 g/cm3 dry density and saturation using distilled water. After distilled water or solution injection, the axial and radial expansion of the bentonite specimens into the simulated rock discontinuities are monitored for one month under free swelling conditions with no groundwater flow. Subsequent flow tests are conducted using the artificial fracture cell to determine the critical flow rate for bentonite erosion. The intrusion and erosion characteristics are modelled using a modified hydro-mechanicalchemical coupled dynamic bentonite diffusion model and a fluid-based hydro-mechanical penetration model.

Compacted bentonite buffer blocks placed in the engineered barrier system for high-level nuclear waste disposal can undergo swelling, intrusion into rock fractures, and erosion with saturation. Bentonite erosion and intrusion can lead to bentonite mass loss via groundwater flow and can ultimately compromise the overall integrity of the disposal system. To ensure the long-term safety of deep geological disposal, it is essential to assess the hydro-mechanical interactions between the bentonite buffer and surrounding rock. In this study, the impact of bentonite erosion and intrusion on the mechanical properties of the jointed rock mass were assessed via elastic wave propagation measurements using the quasi-static resonant column test. Granite rock discs obtained from the Korea Underground Research Tunnel and Gyeongju bentonite were used to simulate jointed rock specimens with different bentonite intrusion conditions. Different degrees of bentonite intrusion were simulated by mixing bentonite and water to create bentonite paste and gel. The longitudinal and shear wave velocities under different normal stress levels were used to quantify the effects of bentonite intrusion on the mechanical characteristics of the rock joint. Complementary numerical analysis using the three-dimensional distinct element code (3DEC) was conducted to provide improved understanding of wave propagation within bentonite gouge-filled rock mass.