Deformation and failure behavior of rock mass around the ventilation shaft in Horonobe URL

Sanada, Hiroyuki; Sugita, Yutaka ; Fujii, Yoshiaki*

EDZ is considered to be important issues in repositories since this is relevant to plug design, support design etc. As a part of the research and development on the geological isolation, JAEA has been implementing the Horonobe URL Project. Deformation and failure behavior around a shaft in URL is described in the paper. Tunnel shape are being measured by a laser displacement sensor to clarify dimension and mechanism of breakouts along the shaft wall. Displacement measurement by extensometers are being carried out to understand deformation behavior in the surrounding rock mass. Breakouts of about 50 cm deep in N-S direction are more frequently observed with excavation depth. The breakout direction was consistent with the maximum horizontal stress which was estimated to be approximately in E-W direction by hydrofracturing tests. Compressive deformation of rock mass also increased with excavation depth. Most part of the deformation occurred within 1 m from the shaft wall.