Result and considerations on the pre-excavation grouting below four hundreds meter depth of the ventilation shaft

Ishii, Yoji; Watanabe, Kazuhiko; Kamiya, Akira; Hayano, Akira  ; Mikake, Shinichiro ; Takeuchi, Shinji; Ikeda, Koki; Yamamoto, Masaru; Sugihara, Kozo

The "Mizunami Underground Research Laboratory" has been carrying out scientific research in granite to establish the technological basis for high-level radioactive waste disposal. To get reliable information on the rock mass geology and hydrogeology and on the bedrock conditions, a pilot borehole investigation was carried out before sinking the ventilation shaft. During this investigation, a zone with high hydraulic head and low hydraulic conductivity was observed at around GL-400m. To reduce water inflow during excavation, pre-excavation grouting with micro-fine cement was done in this region before sinking the Ventilation Shaft. Despite the high hydraulic head and the low hydraulic conductivity, effective reduction of water-inflow was achieved.