Monitoring of pore water pressure and water content around a horizontal drift through excavation; Measurement at the 140m gallery in the Horonobe URL

Yabuuchi, Satoshi; Kunimaru, Takanori; Kishi, Atsuyasu*; Komatsu, Mitsuru*

Japan Atomic Energy Agency has been conducting the Horonobe Underground Research Laboratory (URL) project in Horonobe, Hokkaido, as a part of the research and development program on geological disposal of high-level radioactive waste. Pore water pressure and water content around a horizontal drift in the URL have been monitored for over 18 months since before the drift excavation was started. During the drift excavation, both pore water pressure and water content were decreasing. Pore water pressure has been still positive though it continued to decrease with its gradient gradually smaller after excavation, while water content turned to increase about 6 months after the completion of the excavation. It turned to fall again about 5 months later. An unsaturated zone may have been in homogeneously formed around the horizontal drift considering a degassing.