Evolution and Disaster-Causing Characteristics of Air-Leakage Fractures in Shallow Thick Coal Seams: A Case Study

Composite air leakage from mining-induced fractures is a critical cause of coal spontaneous combustion and gas explosions in a shallow-buried goaf. Physics simulations and numerical calculations were performed to elucidate the dynamic evolution law of air-leakage fractures during mining. The results showed that overburden and surface fractures were the main channels for airflow in the goaf. Additionally, the generation of all fractures was primarily controlled by the key stratum. The dynamic development of overburden fractures was evident during mining, and the fractures underwent opening, closing, and stabilization. The spatial distribution of the overburden fractures was shaped like a double trapezoid. In the low trapezoid, the overall fracture density was high, but the middle fractures were poor because of compaction. In the high trapezoid, horizontal fractures were widely distributed and relatively large, and vertical fractures were mainly distributed on the sides and middle, which were interconnected with the horizontal fractures and penetrated the surface to form composite air-leakage channels. The abundance of fractures from the surface and goaf was the primary cause of multi-source air leakages deep behind the 2421-1 working face in the Baijigou coal mine.