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Low-frequency Vibrations Produced by Surface Mine Blasting Over Abandoned Underground Mines.
Siskind-DE; Stachura-VJ; Nutting-MJ
MISSING :58 pages
Bureau of Mines researchers assisted the U.S. Office of Surface Mining by studying complaint-producing blasting vibrations resulting from an active surface mine operating over abandoned mine workings beneath the surface mine and the nearby town of Blanford, Indiana. Bureau researchers analyzed over 500 blasting records collected by the Peabody Coal Company and the Indiana Department of Natural Resources over a period of 9 months at 7 Blanford residences. To characterize generated and propagated seismic waveforms, the Bureau set up two extended instrument arrays and monitored five production and two specially fired single-charge blasts. Ground vibrations were of high amplitude and dominated by unusual and more structure response- producing low frequencies (4-8 hz) than in previous studies at other sites. These conditions resulted primarily from the geologic structure as the vibration propagating medium. Either the natural horizontal layering and/or extensive horizontal room-and-pillar network underlying the region were trapping seismic energy and determining its character. Blast designs were partly responsible, with high level casting and complex multidelayed blasts producing wave interaction and constructive reinforcement. The traditional 8- ms criteria for separating charge weights per delay appears insufficient for this low-frequency site.
IH; Report of Investigations;
Page last reviewed: April 12, 2019
Content source: National Institute for Occupational Safety and Health Education and Information Division