Study on hydrogeology in the Mizunami Underground Research Laboratory Project; Hydrogeological investigation to evaluate hydraulic characteristic of main-shaft fault

Daimaru, Shuji; Onoe, Hironori ; Takeuchi, Ryuji  

JAEA is performing the Mizunami Underground Research Laboratory (MIU) project. Currently, the project is under Phase II and Phase III. As part of Phase II, the borehole investigation (10MI22, 10MI23) was conducted at 100m Measurement Niche in -300m Access/Research Gallery in 2010. As a result of long-term pumping test, completely different pressures due to the pumping test were observed in monitoring boreholes on opposite sides of the Main-shaft fault. This observation indicates that the normal direction of the Main-shaft fault is low permeable. And, the Main-shaft fault acts as a flow barrier normal to the fault plane. As a result of hydraulic test, permeability of fracture zone with accompanying host rock zone was from 9.4E-7m/s to 3.8E-11m/s. And, this zone was classified as two sections, permeability of the section is same as the upper highly fractured domain (UHFD :1.0E-7m/s) and the section of its permeability is 4 order lower than UHFD.