Studies on planning and conducting for reducing water inflow due to underground construction in crystalline rock

Mikake, Shinichiro ; Yamamoto, Masaru; Ikeda, Koki; Sugihara, Kozo; Takeuchi, Shinji; Hayano, Akira  ; Sato, Toshinori  ; Takeda, Shinichi; Ishii, Yoji; Ishida, Hideaki; Asai, Hideaki; Hara, Masato*; Kuji, Masayoshi*; Minamide, Kenji*; Kuroda, Hidetaka*; Matsui, Hiroya ; Tsuruta, Tadahiko  ; Takeuchi, Ryuji  ; Saegusa, Hiromitsu; Matsuoka, Toshiyuki; Mizuno, Takashi   ; Oyama, Takuya 

The Mizunami Underground Research Laboratory (MIU), one of the main facilities in Japan for research and development of the technology for high-level radioactive waste disposal, is under construction in Mizunami City. In planning the construction, it was necessary to get reliable information on the bedrock conditions, specifically the rock mass stability and hydrogeology. Therefore, borehole investigations were conducted before excavations started. The results indicated that large water inflow could be expected during the excavation around the Ventilation Shaft at GL-200m and GL-300m Access/Research Gallery. In order to reduce water inflow, pre-excavation grouting was conducted before excavation of shafts and research tunnels. Grouting is the injection of material such as cement into a rock mass to stabilize and seal the rock. This report describes the knowledge and lessons learned during the planning and conducting of pre-excavation grouting.