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Matsui, Hiroya; Ijiri, Yuji*; Kamemura, Katsumi*
Proceedings of ITA-AITES World Tunnel Congress 2012 (WTC 2012)/38th General Assembly (CD-ROM), 8 Pages, 2012/05
JAEA has been conducting research and development at two underground research laboratory projects, in crystalline and sedimentary rock at Mizunami, Gifu and Horonobe, Hokkaido respectively. In this report, individual risk assessment methods are shown based on existing studies on general underground construction projects and complementary data and experience obtained from the Mizunami URL project. The results suggest that risk assessments on geological disposal projects can utilize this methodology to assess risk in establishing the site description model for design and safety assessment of a repository, as was done in Phase I of the Mizunami URL. Thus the proposed methodology should have broad application and additional special investigations for risk management are not likely needed.
Tsusaka, Kimikazu; Inagaki, Daisuke; Tokiwa, Tetsuya; Yokota, Hideharu; Nago, Makito*; Matsubara, Makoto*; Shigehiro, Michiko*
Proceedings of ITA-AITES World Tunnel Congress 2012 (WTC 2012)/38th General Assembly (CD-ROM), 8 Pages, 2012/05
In the Horonobe URL Project, three shafts are planned to be excavated up to the depth of 500 m in the Neogene sedimentary rocks. The host rock of the URL site is comprised of diatomaceous and siliceous mudstones, which are the Koetoi and Wakkanai Formations, respectively. Approximately 100 m thick fracture zone with high hydraulic conductivity develops above about 400 m in depth in the Wakkanai Formation. The shaft sinking through the fracture zone is the most challenging issue from the aspect of tunnel engineering in the project. In the fracture zone, there is high possibility of severe breakout and spalling in shaft wall because the shafts might be intersecting faults with the size greater than shaft diameter in addition to low intact rock strength at great depth. In practice, prior to the construction of the Ventilation Shaft through the fracture zone below a depth of 250 m, the three dimensional fault distribution were predicted by integrating borehole investigation results and geological response to pre-excavation grouting operation. The countermeasure was also designed against massive spalling. During the shaft sinking, fracture mapping of shaft wall was carried out in order to evaluate the prediction of fault distribution. Roughness of shaft wall was also measured by three dimensional laser scanner in order to investigate the shape and volume of spalling resulting from the excavation work. Consequently, the Ventilation Shaft has successfully been constructed through the fracture zone. This is because the prediction of fault distribution was accurate, and the countermeasure against concrete lining damage due to spalling was promptly applied.
