Stress evolution and coal seam deformation through the mining of a remote upper protective layer

Protective layer mining is considered to be an effective method to resolve the outburst risk of coal seams, but limited theoretical and experimental results exist for remote upper protective layer mining. To study the effect of the remote upper protective layer mining, a case study of the Renlou Coal Mine is selected. The stress evolution in the protected layer is analyzed using Flac(3D) and is verified by the measurement of coal seam deformation and investigation of the unloading boundary. The results indicate that remote upper protective layer mining induces an unloading of stress within the protected layer, while a stress concentration occurs outside of the unloading area. The coal seam deformation is consistent with the stress evolution, for which the maximum compressional and expansional deformation are 0.5 parts per thousand and 7.19 parts per thousand, respectively. The gas pressure decreases significantly as a consequence of these applications, following which the gas pressures within the theoretical unloading boundary are 0.30 MPa and 0.35 MPa along-strike and along the tendency of the protected layer, respectively.