ベンチカット発破に起因する発破音の発生機構について

抄録

Blast noise is now under public discussion as one of the most troublesome problem. For reducing of a blast noise, it is necessary to make the emissive mechanism clear. Then, in this paper, the emissive mechanism is discussed. The results obtained are itemized below. We conclude the blast noise caused by a quarry blasting is ascribed to a refraction wave which is emitted into the air from a bench surface near the burden by the arrival of a strong stress wave caused by an explosion. By measuring the maximum particle velocity at the intersection of a burden and a bench surface, the value of 165 dB is obtained as the peak pressure level of a blast noise at the bench surface near the burden. By taking a picture of a fragmentation and measuring the pressure level of the blast noise, it is concluded that the particular area in the blasted bench surface may be regarded as a surface sound source where the noise having pressure level of 165 dB is projected. The size of the sound source of which shape is almost rectangle can be regarded as follows for the case of an instantaneous blasting of a single row. Vertical length: the length between the lower level of the bench and the upper end of a charge. Horizontal length: the spacing of charge hole times number of holes those are fired instantaneously.
Furthermore, comparison of a peak pressure level and a root mean square pressure level is made, and the following ratio is obtained.
dB (Peak): dB (Impulse): dB (Fast) =1.08: 1.04: 1.0