Breaking Mechanism of Longwall Mining Face Roof under Room-and-Pillar Goaf of Shallow-buried Short Distance Coal Seams and Its Control

For the problem that large area impact weighting may occur in the longwall mining face roof under room-and-pillar goaf of shallow-buried short distance coal seams, theoretical analysis method is adopted in establishing a mechanical model for roof under concentrated stress of residual coal pillars to carry out research on the deformation and damage of overlying strata caused by longwall mining under room-and-pillar goaf of shallow-buried short-distance coal seams, the impact weighting caused by aggregation of rock mass elastic energy and mechanism of support crushing and etc. The results of the research show that: under the action of concentrated stress of residual coal pillars, the interval of initial roof breaking of longwall mining face roof under short-distance room-and-pillar goaf is shorter than that under the action of uniform load (mining conditions for single coal seam), and the interval of periodic roof breaking varies in certain range; and in order to control the rock mass elastic energy aggregated due to impact weighting, the working resistance of support is 20% higher than that of single coal seam mining. The results of the research are applied in 3-1-1 and 3-1-2 shallow-buried short-distance coal seams of Shigetai Mine of Wulan Coal Group. After the room-and-pillar mining method is adopted for the overlying 3-1-1 coal seam, it is determined that the initial weighting interval of the longwall mining face of underlying 3-1-2 coal seam is 18.96 m, the periodic weighting interval is 8 to 12 m, and the mining face support resistance is 6800 kN. At present, more than 3 million tons of coal has been successfully mined and the supports operate well in general, which provides theoretical basis and practical experience for safe mining under similar conditions.