Study on groundwater flow and transport properties considering the structural change of fracture system in rock masses.

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It is commonly accepted that fluid flow in granitic rocks mainly occurs through discontinuities such as joints, fractures and cracks. However all of discontinuities are not always the conduits. How do the fluid flow path form? The investigations of fracture system in Stripa mine, Aspo Hard Rock Laboratory and Kamaishi Mine suggest that fluid flow path mainly relates to the displacement along the fractures and in situ stress regime.The effect of shear deformation on hydraulic properties of Miocene sandstone, Shirahama Ss, was investigated in drained triaxial compression experiments. Flow pump method developed by Olsen et al. (1985) is adopted in order to measure the hydraulic conductivity. The water to permeate was run out to two directions, that is the loading direction and the vertical to loading. These tests show that hydraulic conductivities at the peak stress for both tests increase about three times as large as the initial ones. The difference of hydraulic properties due to flow direction is now in consideration.In order to examine the deformational and hydraulic properties of rock with fracture system, we developed the triaxial testing machine, in which the surface microstructure of specimen can be observed in a motion using a stereoscopic microscope. In this present study we first showed some experimental results in uniaxial compression test. The shearing process on fractures experimentally generated is simultaneously observed by stereoscopic microscope. The rotation and cutting of bridge, sliding on fracture plane and opening of fracture occur. Furthermore it is clear that these structures are continued inside the specimen by thin section observation. Next, permeability tests under triaxial compression were conducted for fractured Shirahama sandstone. The tests show that the slide along fractures mainly occur after the peak stress and hydraulic conductivity abruptly increase.