The results of the investigation on rock mechanics in AN-1 and MIU-1 boreholes

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The investigations on Rock mechanics in AN-1 and MIU-1 have been carried out in l998 as a part of the investigations in pre-investigation phase in MIU (Mizunami Undergroud Researeh Laboratory) project. The objectives of the investigation are: (1)to develop the conceptual model on rock mechanics in pre-investigation phase in MIU project, (2)to obtain the mechanical data of Toki ganite for the design of MIZUNAMI Underground Research Laboratory. The investigations in AN-1 and MIU-1 consist of three part : (1)Laboratory tests for the mechanical properties of rock matrix in AN-1 and MIU-1 boreholes. (2)Stress measurement in laboratory with AE method in MIU-1 borehole. (3)In-situ stress measurement with hydraulic fracturing in AN-1 borehole. The results of the investigations are summarized as follows : *The distribution of rock mechanical properties for Toki granite is not unique and can be approximated by forth term polynomial equation. The distribution of each properties for Toki granite has different trend with each section, where are until 300m, from 300 to 700m and over 700m. *The vertical component of stress tensors are almost equal to the overburden pressure based on the results of stress measurement with AE method. The stress state from surface to 1000m depth is divided into three part, sueh as reverse fault type (0300m), transitional stress regime (300700m) and strike-slip faulting type (7001000m). The average direction of maximum principal stresses from surface to 300m depth is found to be N-S and the direction from 300m depth was N-W direction. The direction is correspond with the direction of maximum compressive axis derived from triangular survey with the region. *Toki granite is larger in the effective porosity and lower in density than that of Kamaishi granodiorite. The magnitude of stress with depth is almost agree with it measured in Kamaishi mine. The results indicate that the damage induced stress concentration around a drift ...