Numerical simulation on the coupling law of stress and gas pressure in the uncovering tectonic coal by cross-cut

During the process of cross-cut coal uncovering, the stress and gas pressure of the coal mass change with time and even lead to coal and gas outburst. This paper establishes a coupled model that includes the equation of coal deformation, gas diffusion, gas seepage and permeability evolution based on the dual poroelastic theory. This model is applied into COMSOL Multiphysics numerical software. The distribution and evolution of the stress and gas pressure in front of the working face can be obtained from the numerical results. The stepped increase mechanism of the combined potential energy in the tunneling process is proposed, which is used to analyze the evolution of elastic potential energy and gas potential energy. The results can be summarized as follows: under natural conditions, an obvious abnormal stress area occurs near the fault, and the stress of the coal seam is greater than that of the rock stratum. Under tunneling conditions, a original stress (OS), stress concentration (SC) and stress reduction (SR) are formed successively in the front of the working face. And correspondingly, the gas accumulates in SC due to the closure of cracks. The distributions of gas pressure pf and pm are approximately the same during tunneling, and they can reach an equilibrium state after 300 days. The coupled effects of stress and gas pressure gradually intensify, so the elastic potential energy and the gas potential energy of the coal continuously accumulate. The combined potential energy of coal increases with tunneling length, and an outburst is very likely to occur when the combined energy exceeds the surface energy of the coal body at the “Key point”. This research is helpful to understand the evolution mechanism of stress and gas pressure of coal seam in the process of cross-cut coal uncovering, and to know the effects of it to the dynamic disaster.