Hydraulic Conductivity Change Analysis of Surrounding Rock Mass in Excavating Research Drift

Goke, Mitsuo*; Tada, Hiroyuki*; Horita, Masakuni*; Wakabayashi, Naruki*

Tono Geoscience Center (TGC), Japan Nuclear Cycle Development Institute (JNC) conducts the Mizunami Undergroud Research Laboratory (MIU) project in order to develop the comprehensive investigation techniques for the geological environment and the engineering techniques in the deep underground application. The purposes of this study were to contribute to the construction of rock mechanical modeling for MIU project. The virtual fracture model based on mechanical property on the Toki granite was applied to the 2-D hydraulic conductivity change analysis in excavating a research drift and a shaft. The crack tensor analysis model was introduced to the stress analysis before the hydraulic conductivity change analysis. The results are as follows: (1) The crack tensor stress analysis showed very small displacement on the perimeter of a shaft and a drift in intact rock mass, while large displacement appeared in fault zone. (2) More than 10 times large hydraulic conductivity from the initial one appeared in the extent of 1m from the perimeter of a drift and a shaft, in the hydraulic conductivity change analysis with the virtual fracture model for the intact rock mass. The maximum increase of hydraulic conductivity was up to 100 times from initial one. The fault zone showed more than 10 times larger hydraulic conductivity in the extent of 4m from the perimeter. (3) The extent of hydraulic conductivity change was affected by the direction of a drift due to the direction of fractures and the initial stress condition. For example, the rate of hydraulic conductivity increased from initial one changed 110 times to 670 times with the direction of a drift, at the side wall of a drift at the depth of 945m. (4) There was no clear effect to reduce the displacement by supports in the drift in intact rock mass.