A Radar Survey at a Granite Quarry to Delineate Fractures and Estimate Fracture Density

Abstract

Borehole radar, both reflection and tomography methods, and GPR surveys were conducted at a granite quarry to delineate rock inhomogeneities, including major fractures, and to estimate the fracture density. The borehole reflection survey used a directional antenna to get the spatial orientations of the reflectors. The center frequency was [Formula: see text] for the borehole radar reflection and tomography surveys and [Formula: see text] for GPR. Through the interpretation of borehole reflection data using dipole and directional antennas, as well as surface GPR images, we could determine the orientation of the major fractures in three dimensions. Portions of the tomography travel time curves exhibited velocity anisotropy, which is uncommon in granite. Comparing the tomography data with Televiewer images showed that the anisotropy effect in this area is closely related to the alignment of fine fissures. From the borehole radar, tomography, and GPR images as well as the distribution of anisotropy, we conclude that the area bounded by the two fractures, MF2 and MF5, has the freshest granite in the surveyed area. This case study demonstrates that a combination of surface, borehole reflection, and tomographic radar surveys can provide the three-dimensional distribution of major fractures and an estimate of fracture density.