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Cross Borehole Stress Measurements in Underground Coal.
Proc 4th Mini-symp on Explosives and Blasting Research 1988 :17 pages
This Bureau of Mines paper addresses the problem of stress waves generated during delay blasting in underground and surface mines. These waves not only fracture the surrounding coal, rock, or other strata, but also impact delayed charges remaining in neighboring boreholes. Until recently the magnitude of wave interactions in underground coal mines remained rational guesswork, hard to directly confirm close to the charge explosion. Utilizing instrumented boreholes with submerged gauges in different fluids, synchronized gauge traces of stress waves through coal were recorded at close range. The gauges were 25 to 125 cm from a single borehole charge, thereby reproducing both typical and worst case mining conditions in underground coal. Wave propagation to the surrounding gauges occurred prior to any significant coal motion. Over 140 gauge records provided the dominant waveform characteristics: magnitude, specific impulse, and relative energy flux. Regression techniques yielded damping constants and scaling relations for the waveform characteristics as a function of propagation distance. The recorded waveforms determine the wave strength at surrounding boreholes, and this ultimately correlates to detonator and charge degradation criteria. Results of this type determine whether or not a particular detonator or explosive is rugged enough for the conditions utilized in mining underground coal, rock, or other strata.
Proc. 4th Mini-symp. on Explosives and Blasting Research, 1988, PP. 16-32
Page last reviewed: April 12, 2019
Content source: National Institute for Occupational Safety and Health Education and Information Division