Rock mechanical investigations in the Mizunami Underground Research Laboratory Project (phase 1)

This report discusses about rock mechanical properties and in-situ stress state before excavation of shafts and drifts, and analysis of surround rock mass behavior in drift excavation based on the results of investigations in Mizunami Underground Research Laboratory Project (Phase I). As results of the research, the rock mechanical properties of the Toki granite at the MIU construction site are; apparent specific gravity 2.30 ∼ 2.65, unconfined compressive strength of 64 ∼ 212 MPa and, Young's modulus of 20∼68GPa. The rock mechanical properties of Toki granite at the MIU construction site are similar to average found in Japanese granite. Directions of maximum principal stress are N-S to NW-SE. Based on these results, analysis was made and modeling method was established for excavation damaged zone in analysis of surround rock mass behavior in drift excavation. After Phase II, changes in distribution of deformation, safety factor, hydraulic conductivity, and opening fracture are caused by drift excavation. (author)