Tensile failure mechanism enhanced by uncovering coal area during coal and gas outburst

Deep mining is imperative, and the consequent coal and gas outburst disasters triggered during coal uncovering are becoming increasingly severe. Therefore, this study investigated the mechanical mechanisms of outburst instability from three dimensions: experiment, numerical simulation, and field application. Based on physical simulation tests with different outburst pore diameter, it was found that the gas pressure relief rate, gas emission volume, and outburst dynamic phenomena increase with outburst pore diameter. The migration patterns of the gas-solid two-phase flow evolved over time approximately into suspension flow, plug flow, dune flow, and stratified flow. The dominant influence of gas-driven tensile failure was amplified by uncovering coal area. The employment of the “fluid-solid-damage” coupling model revealed that coal damage, gas emission volume, deflection angle of outburst hole, roof displacement, maximum horizontal tensile stress, the horizontal tensile stress zone, the peak seepage force, and the damage zone all increased with uncovering coal areas. At the gas pressure of 0.74 MPa, when the uncovering coal areas were 3.189, 4.754 and 6.225 m, the total gas emission volumes were 4.72×10 −4 , 16.83×10 −4 , and 17.67 m 2 /s, deflection angles of outburst hole were 150.79°, 152.89° and 158.66°, the maximum roof displacements were 0.044, 0.046, and 0.325 m, and the peak seepage force were 0.85, 1.27, and 1.46 MPa/m, respectively. The regions of coal failure calculated by tensile failure criterion largely coincided with those calculated by the mixed failure criterion, far greater than those calculated by the shear failure criterion. As the increase of uncovering coal area, tensile weights of 80.72%, 89.78%, and 93.01%, respectively. Comparisons with field outburst cases showed that both gas emission volume and outburst hole deflection angle reflected the tensile failure of coal. The mechanical instability process of outbursts under the influence of uncovering coal area and gas pressure was analyzed, developing the progressive cyclical method of coal uncovering, which provided a novel approach for the achievement of safe coal mining.