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Assessing Presplit Blast Damage With Crosshole Seismic Tomography.

Cumerlato-CI; Stachura-VJ; Tweeton-DR
Paper in Exp Abs With Biographies 1991 Tech Prog Soc Expl Geophysicists 1991 1:914-917
The U.S. Bureau of Mines has conducted crosshole seismic surveys to assess blast-induced damage at a large western surface coal mine. Surveys were conducted both before and after presplit blasts where standard and modified blasthole loads were used. Data from these surveys were processed using a curved-ray tomographic analysis program developed by the Bureau to produce cross-sectional velocity tomograms of rock masses centered on the presplit blast line. Drillers' logs and postmining stereo photography of resulting highwalls were used to help substantiate results. Preblast tomograms show velocity layering and structures consistent with lithology and other features known from drillers' logs. In the postblast tomogram produced from data collected where the standard blasthole load was used, low-velocity zones are prominent features indicating intense fracture damage to the rock masses on either side of the presplit line. In contrast, the postblast tomogram produced from data collected where the modified blasthole load was used shows little change in seismic velocity, indicating that much less fracture damage had occurred. These results demonstrate that crosshole seismic tomography can be an effective analytical tool for assessing blast-induced fracture damage in the subsurface.
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OP 26-92
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Paper in Exp. Abs. With Biographies, 1991 Tech. Prog. Soc. Expl. Geophysicists, V 1, Pp 914-917