Characterizing Rock Fractures from Borehole and Tunnel Data

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This research will develop and test new methods for using readily available data from cylindrical samples to quantify rock fracture measures. Cylindrical data from boreholes, rock core, tunnels and shafts are widely available but currently under-utilized for rock fracture characterization. Boreholes and core are standard components of geotechnical/geoenvironmental site investigations and petroleum exploration worldwide and borehole-imaging techniques (such as BIPS) are highly developed and rapidly progressing. On a larger scale, tunnels, shafts and wells provide excellent windows into the subsurface rock mass structure. Borehole images, rock core and full-periphery tunnel maps will be used to quantify fracture size, density (number of fracture centers per unit volume of rock mass) and intensity (area of fractures per unit volume of rock mass) - all major components of a unified system of fracture abundance measures. The research results could be used by engineers or geologists to help quantify fracture characteristics from small-diameter cylinders such as boreholes, bolt holes or oil wells, as well to obtaindirect, real-time quantitative fracture data from tunnels and shafts.Methods to be explored include: (1) estimating mean fracture size from the ratio of transections to partial transections of the cylinder by fractures; (2) using the frequencies of intersections, transections and partial transections to quantify fracture density and intensity; (3) combining circular scanlines normal to the cylinder axis with straight scanlines parallel to the axis to create an orthogonal sampling geometry that minimizes orientation bias; and (4) modification of the Terzaghi correction for zero-diameter boreholes to take into account fracture size and cylinder size. These approaches are outgrowths of previous work by the principal investigators on the sampling and interpretation of linear fracture traces exposed on planar surfaces.A key aspect of the proposed work is continued cross-disciplinary research and teaching involving civil engineering and structural geology. This collaboration brings together investigators from two fields that have strong but different interests in understanding rock fractures. A major goal of the proposed research is to meld the two viewpoints together. A key output of the research will the two co-supervised Ph.D. students, who will be cross-trained in rock engineering and structural geology.