Low frequency blast vibrations from Indiana surface coal mines.
Rock Mechanics: Contributions and Challenges: Proceedings of the 31st U.S. Symposium, June 18-20, 1990, Colorado School of Mines, Golden, Colorado. Hustrulid WA, Johnson GA, ed., Brookfield, VT: A.A. Balkema, 1990 Jan; :881-888
Near-surface underground coal mine workings produced long-duration low-frequency surface-type seismic waves through a multiple-reflection trapping mechanism. In addition, one site without underlying workings also produced low-frequency waves by reflections in a thick low-velocity surface layer, consistent with similar observations made by earthquake researchers at other locations. In general, the geologic structure is primarily responsible for the blast vibration characteristics, greatly influencing vibration frequency and having an indirect influence on peak vibration amplitudes through low-frequency wave interference. Blast designs based on controlling delay times had only a limited influence on average vibration amplitudes at distances greater than a few hundred feet for short delay periods with standard accuracies.The 8-ms minimum time separation for independent charges appears too short for low-frequency sites and should not be used in cases of vibrations with dominant frequencies below about 10 hz. Charge weights per delay should be estimated from delays within the time interval T/2, where T is the wave period (1/f). When available, precise delays should be tested to determine if special intervals can be used to reduce generation at the frequency of the trapped surface waves. Standard pyrotechnique delays, with high amounts of statistical scatter, had little or no noticeable influence on vibration frequency. Based on charge weights per 8-ms delay, decking appeared to be ineffective in reducing vibration amplitudes and actually produced higher vibrations at a given scaled distance for both echelon and casting designs than did full column loads.
Mining-industry; Underground-mining; Coal-mining; Vibration-effects; Vibration; Surface-mining; Explosives; Explosions; Rock-mechanics; Geology; Structural-analysis; Wave-propagation; Blasting-agents; Weight-factors
OP; Conference/Symposia Proceedings
Rock Mechanics: Contributions and Challenges: Proceedings of the 31st U.S. Symposium, June 18-20, 1990, Colorado School of Mines, Golden, Colorado