Movement of Overlying Strata and Pressure Relief Effect With the Lower Protective Coal Seam Mining Under the Super Large Spacing

In mining engineering, the protective layer mining is the main method to control coal and gas outburst disaster. However, the lower protective layer mining under an extremely large spacing, which exceeds 150 m, is still not mature enough. Thus, Pingmei No. 10 Mine was taken as an engineering case, to study the movement law of overlying strata and the pressure relief effect. The similar simulation test and numerical simulation calculation were applied to study the fracture and movement of overlying strata, height of three zones and the pressure relief range. Based on characteristics of the on‐site gas extraction parameter, the effect of pressure relief protection was analyzed. The results show that: The fracture of the key strata close to the lower protective layer directly controls the development and extension of the overlying strata fracture, and also directly restricts the height of three zones. The height of the caving zone is 0–43 m, and collapses to the upper part of the key strata. The height of the fracture zone is 43–112 m, and develops to the lower part of the subkey strata. The upper protected layer of Wu coal seam is located at the bending subsidence zone. The inclination Angle for pressure relief is 82°–84°, and the strike Angle is 66°–74°. Finally, working face layout parameters of the upper protected layer in Wu 10‐33190 are designed. The on‐site gas drainage data indicate that: the pre‐extraction rate is 37.55%, the gas content in the Wu coal seam is lower than 6 m ³ /t, and the residual gas pressure is 0.5–1.1 MPa. The gas drainage data prove that the pressure relief effect of the lower protective layer mining under a super large spacing is effective.