Destress blasting in deep mines of NorNickel’s Polar Division

Talnakh and Oktyabrsky ore fields are estimated as rockburst-hazardous starting from the depth of 700 m downward according to safety rules. This means that mining is only permitted within certain protected zones. At the present times, such protected zones are generated in underground mines by means of the large-diameter destressing drilling. Despite proved efficiency, the high cost and large amount of the destressing drilling are the grave faults of this approach. Aiming to save drilling cost, it is proposed to make rock mass rockburst-unhazardous using destress blasting. This article gives a brief description of the destress blasting mechanism. This method has been effectively used in relaxation of pillars from stresses before extraction of the reserves from the pillars both in Russia and abroad. In Oktyabrsky Mine stress relaxation of pillars was implemented by slotting, and the drilling and blasting data were available. This study proposes to destress rock masses by means of directional destress fracturing in horizontal plane through blasting of decked charges of special design. The initial parameters for destress blasting using holes with diameters of 76 and 130 mm are determined. The charge design aimed to ensure a zone of fractures in the horizontal plane, at minimized vertical fracturing is described. This information can be used in planning of full-scale tests to refine parameters and application ranges of the method. For the full-scale tests, it is suggested to undertake destress blasting at different blast patterns on different test sites, and to compare the results with the current destressing method (destressing drilling). Efficiency can be proved using geomechanical and geophysical methods. The authors appreciate participation of V. P. Marysyuk and T. P. Darbinyan from NorNickel’s Polar Division in this study.

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.

Destress Blasting of Rock Mass: Multiscale Modelling and Simulation

In this paper, a multiscale modelling and simulation of destress blasting of rock mass is presented. The proposed and novel approach combines two separate 3D solutions: the first was obtained for the small-scale problem, face(s) blasting process, and the second for the global scale problem, seismic wave propagation within very large volumes of surrounding rock mass. Both the approaches were based on explicit dynamic modelling methodology using the central difference method. In the local case, the arbitrary Lagrangian–Eulerian (ALE) procedure with the Jones–Wilkins–Lee (JWL) equation defining an explosive material was used. For this purpose, a selected volume of a rock mass comprising a blasted mining face was modelled in detail. From the numerical simulation, pressure distribution over the modelled rock was obtained, which was the basis for an initial condition for the global 3D FE model. The peak particle velocity (ppv) distribution obtained from finite element analysis was compared with experimental outcomes. A reasonable agreement between both results was achieved; therefore, the adopted multiscale modelling approach confirmed its effectiveness and that it can be successfully implemented in further engineering practice.