Experimental study on similarity simulation of air leakage and transport in multi-layer composite goaf above and below the shaft

During the mining process of multi-layer composite coal seams, the mining of the lower coal seam causes severe air leakage in the upper goaf, which exacerbates the spontaneous combustion of residual coal in the goaf. In order to prevent the occurrence of coupled disasters of coal spontaneous combustion and gas explosion, similar physical simulation experiments were conducted to study the law of air leakage and transportation in coal mine goaf. A multi-layer composite goaf simulation system was designed. Based on the situation of 22310 working face in Bulianta Coal Mine, simulation experiments were conducted using two ventilation methods: extraction type and pressing type, with controlled air flow rates of 4.4×10−3, 5.9×10−3, 7.4×10−3 m3/min. The distribution patterns of oxygen volume fraction in the goaf under different ventilation methods and the spatial distribution law of coal spontaneous combustion risk areas in multi-layer composite goaf were obtained. The results show that the impact area of oxygen volume fraction in press-in ventilation is relatively large, with high oxygen volume fraction in both direction and inclination, and the impact height is below 0.5 m from the bottom plate; the impact of the extraction type on the oxygen volume fraction in the goaf involves the top layer, manifested as local effects, and the distribution of oxygen volume fraction contour lines presents a “funnel shape”.