Excavation disturbance analysis based on crack tensor model and virtual fracture model for research drift of the Mizunami Underground Research Laboratory

Goke, Mitsuo*; Horita, Masakuni*; Wakabayashi, Naruki*; Nakaya, Atsushi*

The purposes of this study were to contribute to both the evaluation of mechanical stability of a research drift and the plan of future studies. The crack tensor model based on mechanical property on the Toki granite at the Mizunami Underground Research Laboratory construction site was applied to analyze the rock stress as a research drift and a shaft were excavated. The virtual fracture model was applied to the hydraulic conductivity change analysis.The results are as follows:1)In the reference case of a shaft, convergence showed 9.03mm at the GL-500m, and 21.78mm at the GL-1000m. The maximum increase rate of hydraulic conductivity showed about 14 times at the both depth. In the reference case of a drift, convergence of a splingline showed 3.36mm at the GL-500m, and 7.99mm at the GL-1000m. The maximum increase rate of hydraulic conductivity showed a range of about 28 times from about 19 times at the GL-500m, and a range of about 45 times from about 15 times at the GL-1000m.2)As rock class getting weaker, the convergence of a shaft and a drift increased, also the stress in support parts increased, while distributions of the safety factor and the hydraulic conductivity change were almost changeless.3)As the direction of a drift changed to 90 degrees form 0 degrees, the convergence of a shaft and a drift increased, also the stress in support parts increased, and distributions of the safety factor and the hydraulic conductivity change were affected.4)As compared with analytical result regardless of excavation damaged zone, analytical result in consideration of excavation damaged zone showed that the convergence and the stress in support parts increased. Especially, the maximum increase rate of hydraulic conductivity increased remarkably. For example, the maximum increase rate of hydraulic conductivity was 240 times to 400 times at the bottom of a drift