In situ stress measurements in siliceous mudstones at Horonobe Underground Research Laboratory, Japan

Sanada, Hiroyuki; Nakamura, Takahiro; Sugita, Yutaka 

As part of the research and development program on the HLW geological disposal, JAEA has been implementing the Horonobe Underground Research Laboratory (URL) project investigating sedimentary rock formations distributed in Horonobe area, Hokkaido, Japan. The authors have been implementing the research and development program at Horonobe to clarify the in situ stress conditions in siliceous mudstones at the URL. The objective of this work is to establish a strategy for an in situ stress measurement program for geological disposal and to develop an understanding of the in situ stress conditions in the deep underground formed by the sedimentary rocks. The application of several stress measurement methods to the Horonobe siliceous mudstones carried out during the surface-based investigations and the investigations during construction of the underground facilities, as well as information on the initial stress state around the Horonobe URL are described in this paper.