Evolution Characteristics Of Cracks In Coal And Overlying Strata Caused By Mining Of Coal Seams And Their Influence On Gas Drainage

Coal seam group mining,coal and overburden fracture evolution and seepage characteristics are crucial for efficient gas extraction in mines.In this paper,through theoretical analysis,similar simulation,numerical simulation and field verification,the characteristics of coal seam fissure field under coal seam group mining conditions are studied,the overburden mining fissures distribution model are constructed,the coal rock body permeation law under mining action is revealed,the method of determining gas extraction favorable zone under mining action is formed,and the engineering application of unloading gas extraction is carried out.The main research work of the paper is as follows.For the understanding of the coal seam fracture field and seepage field law of coal seam group mining,physical tests of coal rock stress,strain and permeability evolution under two cyclic addition and removal paths were designed.The strain and permeability patterns of single mining and secondary mining coal seams were analyzed.The regional delineation of the seepage field of the fracture field is analyzed.Through the physical tests of fluid-solid coupling,the mechanism of low gas coupling catastrophe in pressurized coal seam is revealed,and the conditions of normal gas outflow,low value abnormal gas outflow and high value abnormal gas outflow and catastrophe are analyzed,and according to the peak stress,the "three zones" of coal seam strain,gas seepage and "three zones" of coal seam strain and permeability are quantitatively delineated in the over-action section of mining."and the dynamic evolution range and characteristics of the "three zones".The similar simulation test method was used to study the mining fracture field and mining stress field of the close coal seam group,to obtain the quantitative trend of the development and evolution of the overburden fracture zone,and to determine the key areas for gas extraction.Through theoretical calculations and 3DEC numerical simulations,we analyzed the off-bed fractures and fracture fractures in the fracture zone,established the structure model of fracture block within the high level annular fractures of mining fractures,combined with the field drilling peeping and other methods,comprehensively determined the development height of the overburden fracture zone and the distribution range of mining fractures,thus giving the analytical solution of the distribution pattern of the two types of fractures along the tendency,and realized the quantitative calculation of the two types of mining fractures.The quantitative calculation of the two types of mining fissures is realized,and the dominant gas transport channels are quantified.Based on the stress micro-unit analysis and superposition principle,the distribution characteristics of overburden stress after the impact of mining are obtained,and the permeability distribution characteristics under the action of mining stress are elucidated through the quantified relationship between stress and permeability,and the permeability distribution under different stress distribution of overburden is determined and the overburden unloading gas transport characteristics are determined through COMSOL numerical simulation.The research results of this paper were verified in the field,and a comprehensive method was developed to determine the location of unloading gas extraction from the overlying fracture zone.