Investigation On Protection Range In Exploiting The Upper-protective Layer Of Inclined Coal Seems

Coal and gas outburst prone Mines increased with the increase of industrial demand and mining depth of coal. Mining protection seam was an important regional outburst defence measure when coal seam group was mined. The existed problems on the protection scope demarcation of upper protective seam in exploiting inclined seam group in Sanhui coal Mine were reviewed. Protection scope demarcating methods on upper protective layer mining in exploiting inclined seam were studied by theory analysis, on-site research, experimental study and numerical simulation.Gas seepage laws were obtained in soft-slicing coal with triaxial pressure system. The seepage velocity and penetrability coefficient appeared changing of the"Z"shape with the increase of the effective axial feed when the confining pressure and gas pressure were constants. As the axial feed and the gas pressure did not change the seepage velocity and penetrability coefficient notably decreased in the form of negative index with the increase of effective confining pressure. For the constant axial feed and confining pressure, seepage velocity increased in the form of power exponent, and permeability coefficient decreased while gas pressure increased.The gas pressure and the gas flow quantity from boreholes were determined at the first Mine in Sanhui. The results were showed that coal seam gas pressure revealed"Four-zone"distribution, and gas flow manifested"M"change after the upper-protective layer was mined. Based on the transition of the gas pressure, the pressure relief angle in the inclined down-protective layer was 74.5°. The prevention scope of pressure-relief angle in coal seam strike along the oblique working face was 52.2°~63.7°.The change processes of stress field and deformation field of the protected seam were simulated by ABAQUS software after the inclined upper-protective layer of the first Mine of Sanhui in Tianfu was mined. In the light of the protection rule of pressure-relieving and normal deformation of the protected seam, the pressure-relief scopes along the inclination and strike were ascertained. The upper and downside stress-relief angles along inclination of upper-protective layer are 74.1°and 72.1°, respectively. The stress-relief angles along inclination of coalface are 51.3°～62.5°. By contrast with spot and numerical simulation results, after inclined upper protective seam mined, the protective pressure-relief angles of protected seam were highly similar, and the result of numerical simulation was safer than that of on-site testing.