Analysis of the Natural Hazard of the Mining Void Zone Based on Incomplete Collapse of the Roadway in the Return Mining

Determining the risk of spontaneous combustion of coal remains in the airspace is crucial to the safe production of mines. Therefore, to investigate the danger of spontaneous combustion in the airspace when the overlying rock layer is not sufficiently compacted, the 1304 working face of Hongyang no. 2 Mine was taken as the research object. The experimental device was developed to measure the oxygen consumption rate, and the negative exponential function model was used to analyze the change rule of the oxygen volume fraction of the coal samples. Combined with a large amount of measured data of the working face and the change of the wind speed of the inlet and return tunnel, a CFD model of the ground without subsidence of the bubbling medium of the mining airspace was established, and numerical simulation was carried out on the flow field of the working face’s airspace area by using FLUENT software to get the oxygen volume fraction distribution law of the airspace area distribution law. The results show that the continuous oxygen consumption rate of the coal sample is γ = 9.3381 × 10^–7 mol/(m³ s). Then, the oxygen volume fraction of choking (critical) under the actual temperature is 14.4%. The maximum range of the spontaneous combustion oxidation zone in the goaf is 25 to 176 m away from the working face. The work safety advancement rate is 1.86 m/d, and the actual advancement speed is 9.6 m/d, which also presents a lower risk of spontaneous combustion. The on-site test data matches well with the simulation results, which verifies the validity of the simulation and provides a basis for the prevention and control of spontaneous combustion of the coal left in the mining area to ensure the safe production of the mine.