The Key Influence Factors Of Protective Layer Mining Effect Evaluation

High gas content and low permeability coal seam is easy to cause gas outburst accident during its mining and reduce the coal mine production efficiency. Protective layer mining technology can reduce the gas content and pressure of the protected coal seam effectively. But the different protective layer mining conditions, the different protection effects to the protected coal seam. Therefore, this article aimed at the main influencing factors of the protective layer and used numerical simulation method to study the effect of various factors. At the same time, basic mechanics tests were carried out to provide reference for numerical simulation. Finally, used the analytic hierarchy process to evaluate the weight value of factors and judging the influence degree of various factors. The following preliminary conclusions:(1) Sandstone and mudstone strain mainly presents the pore pressure deformation stage and elastic deformation stage in the process of uniaxial compression and Brazilian splitting, no significant yield stage, showing strong brittleness.(2) Under different layer spacing conditions, the protected coal seam presented stress concentration phenomenon nearby the cutting hole and working face. The protected coal seam got minimize stress at the central mined-out area and its vertical stress change rule presented certain symmetry. With the increase of layer spacing, the protected coal seam biggest expansion rate reduced and pressure relief range reduced. Overburden rock fissure field presented ladder form, and the fracture belt width of cutting hole less then the fracture belt width of working face. But fracture belt angle of cutting hole slightly larger then the working face. The fracture belt width and angle were closed under different layer spacing conditions.(3) When the coal seam dip angle is small, stress of the upper seam were unloaded more fully. With the increment of dip Angle of coal seam, the protected seam biggest expansion rate reduced, but pressure relief range increased. Overburden rock fissure field also presented ladder form. With the increment of dip Angle of coal seam, the fracture belt width increased and the fracture belt angle decreased. At the same time, the influence height of fracture belt decreased.(4) With the increase of the key layer number, protected coal seam biggest expansion rate reduced, but pressure relief range were basically the same. Meanwhile, overburden rock fissure field also presented ladder form, the fracture belt width and angle were relatively closed. But the influence height of fracture belt and compacted zone decreased, and the range of stratifugic fissure zone which above the mined-out area increased.(5) The factor of layer spacing mainly affect the protected coal seam relief range. The coal seam dip angle mainly affect the protected coal seam expansion rate and the fracture belt height. The key layer number mainly affect the protected coal seam expansion rate. The largest affect of the protective layer mining effect is coal seam dip angle, followed by the key layer, and the last is layer spacing.