Safety Eng. Dept. Natl. Inst. for Resources and Environment, 16-3, Onogawa, Tsukuba 305, Japan
A blast sound propagates over a long range, because of its large sound power of sources and low-frequency components. Blasting operations are often conducted at a hilly side and as a result, sometimes the sound of the blast influences the life environment beyond the hilly undulations. At both hilly sites with heights of up to several tens of meters and flat lands, excess attenuation of blast sound was measured at points of several hundred meters away. Frequency spectrums of excess attenuation beyond the hilly side show that (1) up to around 100 Hz, excess attenuation increases in proportion with frequency, and for more than 100 Hz, it shows mostly constant values of around 40 dB; (2) shapes of frequency spectrum of the excess attenuation show similar pattern with the ones of flat land; and (3) shielding effects of hills mainly appear at the frequency range around 100--250 Hz. From these results, the authors discuss the possibility of sound propagation modeling by extending usual models for flat land.