Strata movement and stress evolution when mining two overlapping panels affected by hard stratum

Mining causes stress redistribution and stratum movement. In this paper, a numerical model was built according to the geological conditions in the 12th coal mine in Pingdingshan city to study the strata movement and the evolution of stress when mining two overlapping longwall panels, named panels #14 and #15. The strata close to the mined panel move directly towards the gob, while the strata that are farther away swing back and forth during the mining process. The directed movement and swinging can break the transverse boreholes for gas extraction; a surface borehole should not be within the range of directional movement. The stress evolution suggested that the mining of the lower panel #15 after the upper panel #14 would further increase the de-stressed range, while the stress concentration around the mined panel would be increased. Hard strata usually carry a greater stress than adjacent rocks and soft coal seams. The stress in a hard stratum increases greatly, and the stress decreases greatly in the coal seams below the hard stratum. This study supplies a reference for similar coal mines and is useful for determining the de-stressed range and transverse borehole arrangement for gas extraction.