Justification of the parameters for safe blasting of floor rocks in the roadway driven through the hazardous by outbursts sandstones

Abstract

In this article, the authors provide the substantiation of the parameters for safe floor rocks ripping by drilling-and-blasting technique in the roadway driven through the hazardous by outburst sandstones by way of forming an unloaded (nonhazardous by outburst) zone from the side of previously driven roadway. The nomogram of numerical values of stresses is given for the conditions of the Pokrovskoe Mine, 1st northern belt road, panel No. 11. From the given calculations, radius of the unloaded nonhazardous by outburst zone in the vertical and horizontal planes around the driven experimental roadway of the 1st northern belt road, panel No. 11, was obtained with accounting anisotropy, depth of mining operations and rate of deformation. The analysis of the material presented in the article allows to conclude that the unloading effect of the driven roadway predetermines the safety of mining operations conducted in the hazardous by outburst sandstone, and drilling-and-blasting operations within the calculated protected zone can be performed as in the nonhazardous by outburst zone. In this research, regularities of the unloading effect of the roadways were established, and dependences were obtained to determine boundaries of the unloading zones in specific mining and geological conditions, which should be determined for each concrete roadway to perform the blasting operations. The presented justifications come to the fact that drilling-and-blasting operations used for ripping hazardous by outburst rocks in the roadway floor are carried out in the already unloaded (i.e. nonhazardous by outburst) zone, which is created from the same, previously driven, roadway. That is, it follows that drilling-and-blasting operations will be carried out in sandstone with no outburst hazard. This makes it possible to perform the drilling-and-blasting operations without making the forecast of the mine outburst hazard and without introducing the shock blasting mode, which, in turns, cut the time and labor costs and lead to significant savings of material and technical means. A further research is needed for establishing dependence between the size of the formed unloaded (nonhazardous by outburst) zone around the working roadway in sandstone and depth of mining operations, section of the roadway and time passed since the roadway was driven.