Disaster-causing mechanism of gateroad under ultra-close gob of board-pillar mining working face and its control

In ultra-close multiple-seam mining, stress environment of the gateroad in the lower coalseam is complex due to the combined effects of upper coalseam mining activity and coal pillars, stress in the surrounding rock is highly concentrated and its distribution is very non-uniform; large deformation can occur easily in the gateroad, resulting in roof disaster, even rock burst, water inrush and other fatal mine disasters under special geological conditions. We present a case study on the prevention and control of roof disaster for a gateroad of one longwall working face in 8# coalseam which under the ultra-close board-pillar mining gob of 711 coalseam in Ganzhuang Coal Mine, including reasonable layout and its stability control. Numerical simulation is employed by software of Flac3D to analyze the distribution characteristics of stress in strata below 7# coalseam, including 8# coalseam, after it has been mined by board-pillar mining method. The reasonable position of the gateroad in 8# coalseam is determined by scenarios comparison, i.e., the gateroad is laid out 10m away from the barrier pillar of 7# coalseam in horizontal direction, stress in surrounding rock is relatively small and its distribution is relatively uniform. Supporting parameters design for the non-symmetrical high-stress gateroad under ultra-close gob after 7# coalseam being mined by board-pillar mining method is also studied by numerical simulation. Engineering practice indicates that surrounding rock deformation of the gateroad has been effectively controlled under this case and the working face has been mined safely. Conclusions in this paper can serve as references for gateroad layout and stability contral under similar conditions.