Integrated Application of Borehole Radar Reflection and Resistivity Tomography to Delineate Fractures at a Granite Quarry

Abstract.

To delineate the inhomogeneities including fractures and to estimate the freshness of rock, borehole radar and resistivity tomography surveys were conducted at a granite quarry mine in Korea. Borehole radar reflection images were obtained at five boreholes and we could get high resolution image of fractures. Spatial orientations of fractures, however, could not be attained because of omni-directional characteristic of antennas. Radar tomography method, a very useful method to estimate the freshness of rock, was also applied but we failed to get images of fractures because vertical fractures were dominant in this site. To get tomographic image of vertical fractures, we conducted the resistivity tomography over eight sections. Although resistivity tomography method provides very low resolution image of the subsurface compared to radar method, we could get tomographic images of vertical fractures. Spatial orientations of fractures were easily obtained by joint interpretation of radar reflection and resistivity tomography images, and we could accurately define the fractures in 3-D manner. Moreover, we could estimate the physical property of fractures by resistivity tomograms, which have been used to successfully explain the hydrogeologic setting of granite quarry mine.