Research on overlying strata movement and dangerous area of coal spontaneous combustion in goaf in dual-system coal seam mining

Aiming at the engineering problem of large air leakage in the goaf of 8106 fully mechanized mining face of Yongdingzhuang Mine in Datong Mining Area, numerical simulation method is used to study the movement breaking form and the dynamic evolution of cracks and the expansion range of the double-system coal seam under multiple mining. The goaf connection mechanism reveals the distribution law of the coal spontaneous combustion danger area in the goaf. The results show that the goaf of Jurassic coal seam group is manifested as roof fall, large floor heave and shear failure of the floor near the coal pillar; the mining of Carboniferous 3-5# coal seam will successively cause the breakage and caving of the basic roof, the lower key layer and the upper key layer. After the upper key layer breaks and subsides, the double-system goaf will be connected and lead to air leakage. The breakage period of the lower key layer is 60 m. In the cross section of the crack zone formed between the key layers, the main air leakage channels are divided into dynamic cracks and edge cracks; when there is external air leakage, the coal spontaneous combustion danger area in the goaf is mainly distributed between 100-175 m from the working face, and when there is no external air leakage, the relative area of the coal spontaneous combustion danger zone is greatly reduced and the overall position is moved forward about 30 m in the direction of the working face.