Mizunami Underground Research Laboratory Project; Rock mechanical investigations around the GL.-500m closure test drift

Kuwabara, Kazumichi; Ozaki, Yusuke  ; Matsui, Hiroya 

In the rock mechanical investigations at the Phase II, the research aims at "Characterization of geological environment in the Excavation Disturbed Zone (EDZ)" from the viewpoint of safety assessment. For the research, the specific information of the EDZ such as (1) size and structures, (2) petrophysical/geomechanical properties, and (3) stress state are required. The research also aims at "Characterization of geomechanical stability around tunnel" from the viewpoint of design and construction of underground facilities. For the research, the specific information such as (4) local stress regime, (5) spatial variability of petrophysical/geomechanical properties of rocks, and (6) distribution of discontinuities intersecting underground tunnels are required. The measurement system for rock mass behavior has been manufactured and set for groundwater recovery experiment in the Phase III. This report presents the results of following rock mechanical investigations conducted in FY 2014. In situ stress measurements using Compact Conical-ended Borehole Overcoring Technique were performed at the - 500m stage. Measurement system for rock massdisplacement using optical fiber was installed at the - 500m stage as part of the groundwater recovery experiment.