The estimation of the effectiveness of torpedo blasting based on an analysis of focal mechanisms of induced mining tremors in the Bielszowice coal mine

摘要

Coal exploitation in the Upper Silesian Coal Basin is associated with rockburst hazard. This hazard is minimalized by active rockburst prevention, where torpedo blastings in roof-rocks take very important place. The estimation of the torpedo blasting effectiveness becomes significant under exploitation in difficult geological and mining conditions, where the high danger of rockburst occurs. Pioneer investigations lead to estimate of the torpedo blastings effectiveness on the basis of an analysis of focal mechanisms of the induced mining tremors. The study has been carried out in the Bielszowice coal mine in cooperation with the Faculty of Earth Sciences of the University of Silesia. The torpedo blastings were performed during exploitation of the seam 507 with the longwall 307b. Each blasting provoked a tremor immediately. The parameters of the focal mechanisms for each provoked event were estimated by the FOCI software. Beside tremors foci with an explosive mechanism, related only to the detonation of an explosive, the occurrence of tremor foci with a shear mechanism has been confirmed. Shear mechanism in provoked tremors proves that blastings caused the motion of rock masses, what is connected with stress drop in the rock mass. The results have been associated with geological and mining conditions.