| The combination of pressure relief mining in protective layer and gas extraction is an effective method to realize safe and efficient mining of high gas coal seam group.The stress seepage characteristics under the condition of repeated loading and unloading of coal and rock mass with different degree of damage is the key problem of multi-protection mining of coal seam group,which directly affects the success and effect of pressure relief mining of protective layer.Therefore,the theoretical analysis,laboratory test,numerical simulation and so on a variety of research methods were adopted to study detailedly the stress and seepage characteristics of coal-rock mass and the influence of key strata under high gas coal seam group mining with multiple protective layers based on multiple protective mining geological conditions of high gas seam group in 1930 coal mine of Xinjiang province in this paper,the results of the study for gas coal seam mining group of multiple protection provides a theoretical and experimental basis.The main innovative achievements of the paper are as follows:(1)The evolution rules of displacement field,stress field and fracture field in coal seam group multiple protection mining have been obtained.The stress variation rules of coal seams and rock formations at different distances from the protective layer during the multiple protection mining of coal seam group have been mastered.The seepage damage law of different damaged coal samples in nine kinds of different loading and unloading paths(repeated loading and unloading under the real stress path of coal mass in fracture zone and bending subsidence zone,constant pressure cycle loading and unloading,step cycle loading and unloading,step by step increase cycle loading and unloading,cross cycle loading and unloading,axial pressure remains constant and the confining pressure unloading,axial pressure increases and confining pressure unloading,axial pressure and confining pressure are simultaneously unloaded)has been revealed.(2)The percolation characteristics of coal body under repeated loading and unloading with different degree of damage have been expounded.The influence of different factors(axial pressure,confining pressure and gas pressure)on the permeability of elastic coal sample has been analyzed.The order of sensitivity of axial seepage permeability to various influencing factors(axial pressure,confining pressure and gas pressure)has been determined under isobaric and deviatoric stress conditions.(3)The relationship between strain,porosity,hulking coefficient,compaction degree and stress in the process of compaction has been obtained.The movement law of broken coal and rock particles during compaction has been revealed.The particle size gradation and fractal characteristics of crushed coal and rock mass with different mixing ratios under different stresses have been analyzed.The permeability characteristics of broken coal with single particle size and broken coal with mixed particle size under triaxial loading of and the particle size distribution rule after test have been expounded.The energy dissipation law of the broken coal sample in the process of triaxial loading has been mastered.The effects of different influencing factors(particle size,coal-rock mixing ratio,coal-rock mixing mode and loading and unloading times)on the permeability of broken coal and rock mass have been discussed.(4)Six kinds of movement types of key layer of protective layer working face have been put forward,and the calculation formula of reasonable working resistance of each movement type support has been given.The location and thickness of key strata hindering the pressure relief of multiple protective mining have been revealed. |
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