The Seismic Source Parameters of Tremors Provoked by Long-Hole Destress Blasting Executed During the Longwall Mining of a Coal Seam Under Variable Stress Conditions

The underground mining of coal seams in the Upper Silesian Coal Basin is carried out at great depths and mostly in the presence of remnants or edges of other surrounding coal seams, i.e. under the condition of high stress level in the rock mass. Therefore, this mining is accompanied by rockburst hazard and suitable preventive action is required. Long-hole destress blasting plays an important role and is commonly applied in rockburst prevention in underground hard coal mines. Estimated blasting effectiveness is important when designing rockburst prevention. It is commonly estimated on the basis of the seismic energy of a provoked tremor. The seismic source parameters have already been considered for this purpose. Additional information about the effects of long-hole destress blasting could be contemplated in the planning of active rockburst prevention. The seismic source parameters of tremors provoked by long-hole destress blasting have been calculated and are presented in this article. Destress blasts were performed during the longwall mining of coal seam no. 506 in one of the hard coal mines in the Upper Silesian Coal Basin. They were executed from the longwall face, in order to destress the rock mass ahead of it. Parameters of the blasts were variable and they were modified according to geological and mining conditions and the observed level of rockburst hazard. The seismic source parameters have been determined for tremors provoked directly after firing explosives and for tremors occurring in the waiting time, and they have been compared with each other.

Influence of Seismic Source Parameters on the Excitation Wavelet in Seismic Explorations Based on Numerical Simulation

Explosives are the most common seismic source in seismic explorations, whose excitation effect is closely associated with their properties, weight, buried depth, and charging constitution. This study analyzes the influence of seismic source parameters on the features of the explosion wavelet. The explosion process of the seismic source in marine carbonate is numerically simulated with the finite element software LS-DYNA. We consider three parameters, including buried depth, charge weight, and decoupling coefficient. To verify the simulation outcomes, we also carry out field observations. The appropriate buried depth of the explosive should be determined according to stratum lithology. As the charge weight increases, low-frequency energy of the source wavelet increases rapidly. The optimum charge weight is 16–18 kg, and the ideal charging structure is in a concentrated, short-column shape. Compared with the buried depth and charge weight, the decoupling coefficient shows more noticeable influence on the excitation effect of the source wavelet, and the optimum coefficient lies between 2.5 and 3. The results of this study may provide reference data for designing explosion parameters in field seismic explorations.