Study of specific energy for evaluation of in-situ rock mass properties (Joint research)

For the research and development about high-level radioactive waste disposal, it is important to evaluate the mechanical stability and the long-term behavior of in-situ rock. Furthermore, in excavating a gallery in deep underground, an excavation disturbed zone (EDZ) develops around the opening with new cracks due to both stress redistribution and excavation induced damage. It is assumed that EDZ becomes the selective path way of groundwater and material, so it is necessary to evaluation properties and distributions of EDZ. Therefore, it is important to conduct investigations to evaluate in-situ rock properties around gallery. However, the in-situ investigation of rock properties is time consuming and costly, so it is difficult to conduct many investigations even though underground gallery is large-scale. For this reason, evaluation of rock properties based on Specific Energy using mechanical data from an excavation machine is carried out. This report describes the results of the joint research carried out in FY 2010 to FY 2012. In Chapter 1, we provide the overview and the background of this study. In Chapter 2, results of evaluation of rock properties in the research gallery at a depth of 500m in Mizunami Underground Research Laboratory (MIU) based on Specific Energy using a hydraulic rock drill are described. In Chapter 3, results of laboratory tests using a hand drill for evaluation of rock properties based on Specific Energy are described. Furthermore, in-situ tests are carried out in the research gallery at a depth of 300m in MIU, and compared with results of laboratory tests. Finally in Chapter 4, the result of joint research is summarized, and the future study is described. (author)