Dangerous Area Evolution and Coal Spontaneous Combustion Prevention Method Induced by Air Leakage in Goaf of Ultra-Long Working Face

Coal spontaneous combustion in goaf seriously affects the safety of mine production, and air leakage is one of the prerequisites for coal spontaneous combustion. Taking the ultra-long working face with a length of 410 m as an example, due to the insufficient compaction degree of the goaf, the high development of large-scale cracks, and the large air flow pressure difference between the intake and return air, the air leakage law in the goaf is not clear, and the risk of spontaneous combustion of broken residual coal increases. Based on the physical and mechanical parameters of coal rock, this paper studies the plastic failure and fracture development in the goaf under various stress disturbances in ultra-long working faces. The laws of gas migration and air leakage in goaf of ultra-long working face was studied by means of field test and numerical simulation. Based on the theory of coal-oxygen composite in goaf, the dangerous areas of coal spontaneous combustion in goaf with different mining sequence evolution of ultra-long working face were determined. Based on the distribution of air leakage flow field and coal spontaneous combustion danger zone in goaf, the comprehensive fire prevention and extinguishing technology of nitrogen injection inerting, plugging and leakage reduction was applied in field demonstration, and the application effect was verified. The research results show that the plastic failure range of overlying strata in goaf presents "saddle shape." The permeability and porosity increase gradually from the middle to the surrounding direction, showing "O-ring" distribution. The main air leakage channels are concentrated at the intake air tunnel corner of the goaf and 160-200 m of the working face. The air leakage sinks are located at a distance of 20-80 m along the dip direction of the working face and at the return corner of the working face, respectively. The average air leakage is 268 m3/min and 153 m3/min, and the maximum width of the coal spontaneous combustion danger zone in the goaf during the dynamic advancement of the ultra-long working face is 107 m. Through comprehensive fire prevention and extinguishing techniques such as nitrogen injection for inerting and filling with high-molecular-weight gel for sealing and leakage reduction, the prevention and control of coal spontaneous combustion in ultra-long working faces at different mining sequences under corresponding engineering backgrounds are effectively ensured.