The results of the geomechanical investigations in the MIU-3 borehole and the conceptual geomechanical model of the Toki granitie in Shobasama area

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Geomechamcal investigations have been carried out since 1998 in 1000m depth surface boreholes as surface-based investigation phase in Mizunami Underground Research Laboratoly(MIU) project. The objectives of the investigation are: (1)to develop the conceptual geomechanical model in this phase of MIU project, (2)to obtain mechanical data on the Toki granite for design of the underground research laboratory. The geomechanical investigations in MIU-3 borehole were carried out in 2000 and focused on the major reverse fault, Tukiyoshi fault intersected at approximately 700m depth in MIU-3 borehole. The investigations consist of three parts: (1)Laboratoly tests to determine the mechanical properties of the rock matrix. (2)Stress measurement in the laboratoly using the AE method. (3)In-situ stress measurement using the hydraulic fracturing. This report describes the results of the geomechanical investigations in the borehole and laboratory. Additionally, integration of the geological, geophysical and geomechanical investigations in AN-1, MIU-1, MIU-2 and MIU-3 boreholes is attempted to establish a conceptual geomechanical model of the Toki granite, The results are summarized as follows: *In MIU-3 borehole, the distribution of the mechanical properties in the granite changes with depth in definable sections from the top of the granite to 300m, from 300 to 600m and over 800m. The hanging wall of the Tukiyoshi fault (to 600m depth) can be divided into two section. The mechanical properties of the granite in foot wall of the fault is estimated with similar properties of the granite in hanging wall of the fault. The results of the seismic velocity measurements of the cores in two dimension show that the degree of the anisotropy in the rock matrix are different between the hanging and the foot wall of the fault. *In MIU-3 borehole, the vertical component of stress tensors is changing near the Tukiyoshi fault and it is lower than the overburden pressure in the foot wall of ...