Abstract: Gas pressure is one of the important factors that induce and aggravate coal and gas outburst(referred to as outburst). In order to further reveal the effect of gas pressure on outburst coal bodies in tectonic zones, uniaxial compression tests of outburst coal bodies under gas pressure (spanning from 0 to 2.4 MPa) gradient were carried out. In conjunction with PFC discrete element numerical simulation, a systematic analysis was performed to investigate the influence mechanism of gas pressure on mechanical properties, damage evolution, crack propagation and energy evolution of coal bodies. The results show that gas pressure significantly diminishes the strength of outburst coal bodies. Both the uniaxial compressive strength and elastic modulus exhibit a nonlinear decline with increasing gas pressure, with maximum reductions of 15.85% and 34.47%, respectively. Based on the damage variable defined by the cumulative count of acoustic emission events derived from simulations, the coal fracturing process can be categorized into four stages: pore fracture closure, micro-crack initiation, propagation, and coalescence. The acoustic emission signals transition from weak to strong, while the damage variable at the peak point decreases as gas pressure increases. Through a collaborative analysis of both experimental results and simulation results, it is found that the failure mode of outburst coal bodies is predominantly governed by gas pressure. This failure mode can be categorized into two types: tension-shear-slip conjugate failure (occurring at gas pressures of 0,0.4,1.6, and 2.0 MPa) and compression-shear-tension-slip conjugate failure (observed at gas pressures of 0.8,1.2, and 2.4 MPa). Notably, the crack density under compression-shear-tension-slip conjugate failure is markedly higher compared to that under tension-shear-slip conjugate failure. Gas pressure significantly affects energy storage and dissipation. Specifically, at low pressure (ranging from 0.4 to 2 MPa), adsorbed gas reduces effective stress and consequently weakens the energy storage efficiency. Conversely, at high pressures (spanning from 1.6 to 2.4 MPa), there is a substantial increase in both energy accumulation and release intensity, thereby sharply elevating the risk of outburst.

Key words: coal and gas outburst, tectonic zone, gas pressure, damage evolution, acoustic emission parameters, discrete element method