Mechanism of deformation-induced damage and gas permeability enhancement of coal under typical mining layouts

Study on permeability distribution of coalface is of guiding significance in reasonable exploitation of gas. An equivalent mechanical model is established by simplifying the characteristics of pores and cracks. From the establishment of the equivalent mechanical model for a standard cylindrical coal-rock specimen, the equivalent formulas for axial, radial and volumetric strains are derived for coal-rock samples containing a single crack, and then are extended to the application in a variety of media combinations containing multiple cracks. The theoretical mechanical model shows good reliability by experimental verification. Based on the prototype of 11-2 coal seam mining face of Zhangji Mine in Huainan, the peak concentration factors of abutment pressure under three typical mining layouts are obtained by numerical calculation. An expression for the distribution of abutment pressure and horizontal stress is derived considering different mining layouts, different stages and volume expansion induced by mining. By establishing a polynomial relationship between volumetric strain and permeability, the distribution of volumetric strain and permeability under different mining layouts is obtained, and divided into different stages according to their various characteristics. It may provide a theoretical basis for the coal mine methane.