Coupled thermal–hydraulic–mechanical–chemical modeling for permeability evolution of rocks through fracture generation and subsequent sealing

The coupled THMC model, interface for pressure solution analysis under coupled conditions, IPSACC, that was proposed by the authors and can describe the long-term evolution in rock permeability due to mineral reactions (i.e., pressure solution and free-face dissolution/precipitation) within rock fractures, was upgraded in the present study by incorporating the processes of fracture initiation/propagation. The remarkable characteristic of the proposed model is its ability to simulate the generation of fractures and the mineral reactions within the generated fractures as well as the subsequent changes in permeability. The proposed model was applied to predictions of the long-term changes in the permeability of rock located near high-level radioactive waste within a geological repository. The predicted results revealed that fractures were generated near the disposal cavity and that the permeability of the damaged zone increased significantly more than that of the intact rock during the excavation, while the permeability in almost the entire damaged zone decreased by about one order of magnitude due to pressure solution at the contacting asperities within the rock fractures after setting virtual radioactive waste into the disposal cavity. Overall, it was clarified that the proposed model is capable of calculating the permeability evolution of rock through fracture generation and subsequent sealing due to mineral reactions at the actual field scale. Thus, the potential for using the proposed model to examine the long-term performance of natural barriers for delaying the transport of radionuclides has been shown.