Abstract

Japan Atomic Energy Agency (JAEA) has started to construct an underground research laboratory in the Neogene sedimentary rocks in Horonobe in 2005. In the end of 2008, the ventilation shaft and one of the access shafts have been reached 250 m and 140 m in depth under the ground surface, respectively. During the shaft sinking, the displacement on a wall and in the surrounding rock mass, and the stress of support members are measured in order to estimate support requirement and the development of loosening zone around the shafts. From the viewpoint of the observational construction, the authors built the relationship among the initial deformation rate, the final deformation and stress of concrete lining as one of the practical guides of shaft sinking. It consists of four categories, Class IS, to IVS, and is useful to predict the rock mass behavior and stress of lining caused by excavation at the earlier stage.

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