Study On Released Range And Gas Drainage Of Close Lean Upper Protective Layer

At present, the protective cover is the best effect, the easiest execution, the lowest cost way to prevent coal and gas outburst. However, how to accurately defined the scope of protection and how to drain the gas has become a key technology.According to protective layer theory mine, ground pressure, flow theory and the theory of coal and gas outburst, the paper analyzed the mechanical property of the protective mining from close range. This paper used numerical simulation method, obtained the stress transformation and distribution law of the upper protective coal mined. Protected coal seam experienced four areas, virgin rock stress, bearing stress, decreasing stress, restoring stress. A certain range of distressed zone appeared in the roof and floor in mined-out while region of stress concentration appeared in the both ends of goaf. Along with the advance of mined-out area work below roof-floor expanded, produced discharging pressure increase through and flow'effect. With the mining goaf forward and the stability of the roof and floor of the strata movement, the stress in coal and rock volts and corresponding recover gradually. Along with the work surface mining in advance, the floor rock each point to undergo compression, expansion, the deformation and failure to compression characteristics. Under tianrong circumstance,the face toward the roof-floor Angle of 50°; Mining the sloping direction along the roof-floor Angle for 71°and 55°.By mining upper protective layers of coal seams in the Shen Hua Tian Rong coal, which can reduce the gas pressure effectively and eliminate the danger of the outburst coal seam. Thus both safety and high-efficiency in mining ensured in mining ensured. According to the investigation results, the scope of cover under the protection of gas pressure reduced from 2.3 MPa to 0.62 MPa, gas recorery valueΔh2, the averageΔh2 and K1 are lower than the index values.The result of this paper provides the theory basis and the reference for the similar mining geological conditions.