The influence of the features of outburst-prone rocks position in the floor of the stope on stress fields and degasation process

Abstract

Rock-gas outbursts happen when mine workings are driven near low-permeability sandstones, which contain gas under high pressure, and most of such outbursts are triggered by shot firing. In particular, when sections of the powered support are clamped in the stope, it is necessary to explode the rock under them, which is dangerous if the outburst-prone sandstone is located in the floor of the stope. One of the factors causing the rock-gas outburst is a certain combination of the stress-dependent permeability of the sandstone and the near-floor rock and gas pressure. Therefore, the purpose of the work is to study the change in the stress state of the host rocks and gas filtration process in the outburst-prone sandstone located in the floor of the stope, with different composition of the near-floor rocks. To achieve the goal, methods of numerical simulation of time-dependent processes of elastic-plastic deformation and gas filtration were used. A stope with sections of the powered support was considered, in the floor of which siltstone and outburst-prone sandstone are located. The computations were performed with variations in the thickness and strength of the siltstone bed above the sandstone. It is shown that the values of the maximum and minimum components of the principal stress tensor gradually decrease in the floor of the stope, the sandstone is unloaded from the rock pressure. This leads to an increase in its permeability, the start of the methane filtration and degasation process. The composition of near-contour rocks greatly affects the distribution of geomechanical and filtration parameters. In the presence of the siltstone bed with a certain strength, a not unloaded bridge with lower permeability appears above the sandstone, and its degasation slows down significantly. If the thickness of the siltstone bed increases, the width of this bridge also increases, and methane filtration in the floor of the stope stops. In this case it is an obstacle that delays or completely prevents the degassing of gas-bearing rocks that lie below. The results of the above analyses should aid evaluation of potential measures to prevent the rock-gas outburst during blasting operations for the movement of sections of powered support in the stope. A better understanding of this problem could save considerable time and expense for future technological operations in similar mining conditions. Keywords: rock-gas outburst, rock deformation, coupled processes, stope, gas filtration, numerical simulation.