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Title The assessment of damage around critical engineering structures using induced seismicity

Authors Pettitt, W.S., C. Baker, R.P.Young, L-O Dahlstrom and G Ramqvist

Publication Reference 2002, Pure and Applied Geophysics, 159, 179 - 195

Abstract Two large-diameter boreholes have been excavated vertically from the floor of a tunnel at the Äspö Hard Rock Laboratory, Sweden. The two deposition holes will have simulated high-level radioactive waste canisters installed in them in an experiment undertaken to test the retrievability of waste from a proposed repository. Induced seismicity and other acoustic monitoring techniques have been used to investigate the Excavation Damaged Zone (EDZ) around the two holes. High-frequency acoustic emission (AE) monitoring has been used to delineate regions of stress-induced micro-fracturing on the millimetre scale. This is shown to locate in 'breakout' regions orthogonal to the maximum principal stress and clustered spatially around pre-existing macroscopic fractures. Three-dimensional velocity surveys have been conducted along ray paths that pass through the damaged region and through a stress-disturbed zone around the excavation. Induced micro-fracturing and stress disturbance are observed as sharp decreases in velocity as the excavation proceeds through the rock mass. The combination of the high-resolution velocity measurements and the AE source locations has allowed the linking of the velocity measurements to a volume of excavation damaged rock. This then provides a quantitative estimate of the effect of the EDZ on the rock mass.

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Link http://link.springer.de/link/service/journals/00024/papers/2159001/21590179.pdf



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