Evaluation of Ground Vibrations Induced by Military Noise Sources

摘要

Measurements from locations with a variety of ground types were analyzed to determine the mechanisms and levels of the ground vibrations produced by airborne detonations of C4. The measurements show that an early seismic arrival from an underground path is always much smaller than the vibration induced by the air blast arrival. The acoustic-to-seismic coupling ratio for the atmospheric wave is a constant with respect to distance and peak pressure at a given location, but varies from site to site, and is usually between 1 and 13 (mum/s)/Pa. A numerically intense computational method to predict the air pressure spectrum above ground and the waveform shape of the vertical component of solid particle velocity near the ground surface compares tolerably well with measurements at short range (60 m) in grass and snow covered ground. A conservative empirical equation to predicts that the commonly used vibrational damage criteria of 12 or 25 mm/s will be exceeded when the peak positive pressure exceeds 480 Pa or 1 kPa, respectively. Either of these levels is much higher than the Army overpressure damage criterion of 159 Pa (138 dB). Thus in most situations damage from blast overpressure will occur long before damaging levels of ground vibration are reached.