Effect of excavation damaged zone on the long-term coupled thermo-hydro-mechanical behaviors of deep geological repositories in granitic rock masses

This study numerically investigates the influence of the excavation damaged zone (EDZ) on the long-term coupled thermo-hydro-mechanical (THM) behaviors of the Korean deep geological repository (DGR) concepts in granitic rock masses. Using the extent and properties of the EDZ derived from Korean Atomic Energy Research Institute (KAERI) Underground Research Tunnel (KURT), numerical results reveal that the EDZ exerts a minor influence on thermal behavior but accelerates the resaturation of the buffer and backfill due to its increased permeability. Notably, the EDZ leads to a smaller extent of potential rock failure compared to simulation cases without the EDZ. This is attributed to a more pronounced reduction in thermal stresses relative to the decrease in rock mass strengths. A sensitivity analysis reveals that uncertainties in the rock mass stiffness within the EDZ have a more pronounced effect on the predicted rock failure volume than variations in thermal conductivity and permeability have on the temperature and saturation evolutions. Reducing disposal spacing to increase disposal density defined as the amount of disposed uranium per unit area significantly raises thermal loading and the risk of rock mass failure, potentially inducing continuous failure zones connecting neighboring deposition holes and disposal tunnels under relatively weak rock conditions. These findings suggest that while the EDZ may not be a critical factor in determining disposal spacing, DGR designs to enhance the disposal density necessitate careful consideration of the rock mass strength to ensure long-term safety.