A Comparison of the Seismic Effects of Different Blasting Types Executed During the Longwall Mining of a Coal Seam

Underground mining of hard coal seams is carried out in the Polish part of the Upper Silesian Coal Basin with an increasing level of rockburst hazard. This hazard is combated by the application of active rockburst prevention, where long-hole destress blasts take an important role. The seismic energy of the provoked tremors can be a determinant of blast effectiveness. To estimate blast effectiveness according to the seismic energy of a provoked tremor, the seismic effect method, developed for hard coal mines in the Czech part of the Upper Silesian Coal Basin, can be applied. A classification system for the evaluation of seismic effect is determined for the assigned colliery with the use of statistical analysis, in which the energy of provoked tremors and the mass of the explosives used is taken into consideration. This method can be applied not only for long-hole destress blasting, but also for other analogous types of blasting, which may initiate geomechanical processes in the rock mass, e.g. blasting for roof rock falling. In this article, an analysis of the effectiveness of both the long-hole destress blasting and blasting for roof rock falling, performed during longwall mining of coal seam no. 408 in a mine in the Polish part of the Upper Silesian Coal Basin, was carried out. The effectiveness of blasting for roof falling was verified directly in situ. The seismic effects of blasts, after which roof falling was confirmed, were classified according to the adopted scale as, mainly, very good, extremely good and excellent. It can be assumed that the analogous effects of the long-hole destress blasting indicate the occurrence of additional processes, as a result of which the rock mass reaches a new and favourable stress-strain equilibrium state.