An investigation was conducted to estimate the distribution of flow channels in rock mass fractures by injecting resin. The investigation site was Grimsel Test Site in Switzerland; an international underground research facility in granitic rock mass. Two fractures at the site were selected as the target fractures. Two-component resin was injected into the target fractures from packed-off intervals in three boreholes that penetrated the fractures to stabilize the fracture surfaces. A low-viscosity and slow-curing resin was selected to extend the resin penetration into fractures far from the injection boreholes. The resin was doped with fluorescent uranine dye for easy detection in the laboratory. After the injected resin had fully hardened, eight additional boreholes, 131 mm in diameter, were drilled to collect the rock core samples impregnated with resin. The core samples were observed under natural light or ultraviolet light (where the uranine-doped resin glows) to measure the distribution of resin filled in the fractures. The distribution of resin filled in the fractures was also observed along the borehole wall by using a borehole TV camera. In situ injected resin was observed in a large part of the target fractures between the injection boreholes. Because the density of resin differs greatly from that of the intact rock, the three-dimensional distribution of the resin in the rock core samples could be estimated by X-ray CT analysis without damaging the cores. Thin sections were made from the rock core samples and the microscopic structures around the target fractures were observed using a microscope. Combining the results of the above-mentioned investigation, the distribution of the flow channels in the target fractures and the geological structures around the flow channels were evaluated. The above-mentioned procedure was found to be effective for the identification of macroscopic and microscopic structures of flow channels in fractures.

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