Layout model of small panel and large coal pillar for rock-burst prevention and water control under extra-thick and water-bearing key strata

The overlying extra-thick and water-bearing key strata perplex the safe underground coal mining in Binchang mining area. When the mining scale of the panel is large, the breaking and instability of key strata leads to rock burst and a surge in water inflow at the same time in the panel. The layout mode of small panels and large coal pillars can improve the stability of the key strata, but the research on the layout model of small panels and large coal pillars under extra-thick and water-bearing key strata is still limited. Taking the second and third panels of a mine in Binchang as the engineering background, reasonable width of the panel and coal pillars were studied through theoretical analysis, field measurement and numerical simulation. Considering the stability of the panel, isolated coal pillar and the main key strata, a stress analysis model of coal pillar and the flexural deformation model of the main key strata are established, respectively. Accordingly, the critical instability width of panel isolated coal pillar in the current mining scale is 257 m, and the critical mining scale for breaking and instability of the main key strata in the small panel is 537 m. Under the current mining scale, the fractures above the second panel develop to the middle of the main key strata, and the main key strata show the risk of breaking and instability. With the width of isolated coal pillar of the panel increase, the fracture development height of the overlying strata in the third panel decreases. To ensure the stability of the main key strata above the third panel, the panel isolated coal pillar should be set at least 225 m. The stress concentration and energy accumulation degree isolated coal pillar of panel are positively correlated with the width of the isolated coal pillar, but negatively correlated with the mining scale of the small panel. Considering the bearing capacity of coal pillar and the recovery rate of coal resources, the reasonable width of isolated coal pillar is 210-270 m, and when the width is 210 m and 240 m, the reasonable mining scale of the third panel is 490-550 m and 640-700 m respectively. The field practice shows that the actual width of the isolated coal pillar of the second and third panel of the mine is less than the reasonable width, and the stress concentration in the isolated coal pillar is higher, so the roof deep hole blasting and large-diameter drilling in coal seam are used for pressure relief. After pressure relief measure implementation, the stress concentration in isolated coal pillar of panel is reduced effectively, and the pressure relief effect is remarkable.