Investigation of Blasting Vibrations Above Abandoned Underground Coal Mines

摘要

The Bureau of Mines performed a comparative study of nine Indiana surface coal mine sites at eight different mines to determine if the presence of near-surface underground abandoned workings resulted in the generation of adverse long-duration, low-frequency blast vibrations. Bureau researchers used extended seismic arrays to identify the vibration characteristics generated within a few tens of feet of the blasts and also as modified by the propagating medium at distances over 1 mile. Production and specially fired single-charge blasts allowed the determination of natural ground frequency and also the influence of the initiation delay timing. Vibration amplitudes from the production blasts at all sites exceeded historical norms, particularly at the greater distances. This contrasts with the near-normal, single-charge blasts. Apparently, between-hole time delays were insufficient to separate vibrations from adjacent charges for the low-frequency waves present at these sites.