Effects of torpedo blasting on rockburst prevention during deep coal seam mining in the Upper Silesian Coal Basin

In the Upper Silesian Coal Basin (USCB), coal seams are exploited under progressively more difficult geological and mining conditions (greater depth, higher horizontal stress, more frequent occurrence of competent rock layers, etc.). Mining depth, dislocations and mining remnants in coal seams are the most important factors responsible for the occurrence of rockburst hazards. Longwall mining next to the mining edges of neighbouring coal seams is particularly disadvantageous. The levels of rockburst hazards are minimised via the use of rockburst prevention methods. One active prevention method is torpedo blasting in roof rocks. Torpedo blastings are performed in order to decrease local stress concentrations in rock masses and to fracture the roof rocks to prevent or minimise the impact of high-energy tremors on excavations. The estimation of the effectiveness of torpedo blasting is particularly important when mining is under difficult geological and mining conditions. Torpedo blasting is the main form of active rockburst prevention in the assigned colliery in the Polish part of the USCB. The effectiveness of blasting can be estimated using the seismic effect method, in which the seismic monitoring data and the mass of explosives are taken into consideration. The seismic effect method was developed in the Czech Republic and is always being used in collieries in the Czech part of the coal basin. Now, this method has been widely adopted for our selected colliery in the Polish part of the coal basin. The effectiveness of torpedo blastings in the faces and galleries of the assigned longwall in coal seam 506 has been estimated. The results show that the effectiveness of torpedo blastings for this longwall was significant in light of the seismic effect method, which corresponds to the in situ observations. The seismic effect method is regularly applied to estimating the blasting effectiveness in the selected colliery.