Characteristics of blast low frequency noise/infrasound by blast densification method and the comparisons with several evaluation methods for low frequency noise/infrasound

摘要

Experimental results of the generation, propagation and attenuation of impulsive low frequency sounds by underground blasting for preventing the ground liquefaction were described. The effects of the blast sounds to surrounding environments were also examined by the comparisons to several evaluation methods for low frequency sounds, as well as by the field surveys for human responses to the low frequency noises. Rapid and sharp increases of sound pressures, which were generated by the impulsive motion of the ground surface, were observed near the blasting point, and the sound pressure, which were generated by rapid gas burst through the boreholes, followed. At distant receivers, the sounds with relatively high frequencies, which were produced by the ground vibrations, propagated precedent to the sounds described above. Although the sound by the impulsive motion of the ground surface extensively attenuated at the distant receivers, the sound by rapid gas burst was clearly measured. Frequency components of the sounds were predominant in range of infrasound after long-range propagation. The occurrences of secondary noises by the rattling of building fittings and disturbance of sleep were suggested from the comparisons between the experimental results and some thresholds for evaluation of the low frequency noises and from the relationships between occurrences of annoyance and G-weighted sound pressure levels.