Based on the results of mechanical property tests in the MIU-4 (excavation started in 2000 FY), mechanical properties of the Tsukiyoshi Fault and the associated fractured zones are expected to be understood. Also, the validity of the rock mechanics conceptual model is expected to be verified by applying numerical analyses to the model. Furthermore, mechanical properties of discontinuity planes should be assessed by joint shear tests. Physical properties of the in-situ rock mass should be evaluated taking the effects of fractures into considerationto quantify the rock mechanics conceptual model.