Relationship between fault system estimated by the fault-striation analysis of drilling cores and rock mass behavior induced by shaft excavation in the Horonobe area, northern Japan

Tokiwa, Tetsuya; Ishii, Eiichi   ; Funaki, Hironori ; Tsusaka, Kimikazu; Sanada, Hiroyuki

Japan Atomic Energy Agency has been constructing underground facilities since 2005 in the Horonobe area. Before the construction, the rock stress was measured by the hydraulic fracturing method using boreholes. In this area, the result showed that the direction of the major horizontal principal stress was in E-W direction. On the other hand, in shaft excavation, the direction of the predominant diameter reduction was observed in NNE-SSW to NE-SW direction. The difference would be attributed to the fact that fault system in the rock affects the deformation of shaft. The authors applied fault-striation analysis with faults identified on drilling cores. The direction of the major principal stress estimated by fault-striation analysis approximately corresponds to the predominant directions of the deformation caused by the shaft excavation. The result shows that fault system affects rock mass behavior in shaft excavation.