Study on distribution laws of spontaneous combustion zones in composite goafs during mining of shallow-burial and close-distance coal seam groups

To prevent coal spontaneous combustion disasters caused by the connection between the ground surface and fissures generated after the overlapping mining of shallow-burial and close-distance coal seam groups, the Huojitu mine in Shendong mining area was regarded as a research case, and a numerical simulation study was conducted to the evolution law of oxygen content and the distribution tendency of airflow velocity in composite goafs. Results demonstrate that the oxygen content trends in goafs of both the top and bottom coal seams are generally similar. The airflow velocity on both sides of the goafs in both the top and bottom coal seams is symmetrically distributed. Within the goaf of the bottom coal seam, the airflow velocity near the intake and return airways is greater than that in the central section. Conversely, the airflow velocity is higher near the central section than near the two airways in the top coal seam’s goaf. Calculation shows that the maximum widths of the spontaneous combustion hazard range in the top and bottom zones of composite goafs are 200 m and 160 m, respectively. Based on the spontaneous-combustion characteristics of the residual coal, the minimum mining speed of the working face is computed as 6.7 m/day. The results reveal the distribution law of the “three zones” of spontaneous combustion in the composite goaf during the mining process of shallow-buried coal seams, providing a certain reference for preventing spontaneous combustion caused by air leakage in shallow-buried composite goaf.