FRACOD Modeling of Rock Fracturing and Permeability Change in Excavation Damaged Zones

Characterization of Excavation Damaged Zone (EDZ) around an underground excavation is a major research topic for deep geological disposal of medium to high level radioactive waste. Rock fracturing due to excavation and thermal loading and its resultant rock mass permeability change in the EDZ are important aspects in the EDZ characterisation. A new function to predict rock mass permeability change in fractured rocks has been developed and added into the existing fracture mechanics code FRACOD. The new functions in FRACOD has been applied to predict the extent of EDZ and permeability change in the vicinity of the TSX tunnel of URL (Canada), the ZEDEX tunnel of the Äspö Hard Rock Laboratory (Sweden) and the deposition tunnels in crystalline and sedimentary rocks (Japan). The predicted the EDZ and its permeability are consistent with the measurement data of the TSX tunnel. In the validation test against the ZEDEX tunnel results, a broad agreement between the FRACOD prediction and measurements has been achieved. The results from both tests indicate that FRACOD with the new function is capable of realistically predicting the EDZ and permeability change. Following the validation tests FRACOD is applied to studying the EDZ of conceptual deposition tunnels for radioactive waste in Japan.