A Study of risk assessment of rapid inrush of water into the underground facility at the Mizunami Underground Research Laboratory project, 2; Relationship between progress of investigations and cost variation related to water inrush

Onoe, Hironori ; Saegusa, Hiromitsu; Motoshima, Takayuki*; Ijiri, Yuji*; Otsu, Hiroyasu*

In the construction of deep underground facilities in a fractured rock mass, it is important to evaluate the influence of hydraulic and rock mechanical heterogeneities due to faults and joints, based on prior investigations. Risk assessment methodology using a combination of discrete fracture network model with financial engineering theory was developed considering unexpected water inrush, which is assumed to be one, if not the most significant issue for construction in fractured rock. In this study, the relationship between the amount of information due to the progress of investigations and cost variation regarding water inrush was evaluated, and a management method based on the risk assessment is discussed. The project that serves as the basis for the study is the construction of the underground facility in the Mizunami Underground Research Laboratory (MIU), which is now under construction by the Japan Atomic Energy Agency (JAEA).