The Damage And Seepage Flow Characteristics Of Coal Under Conditions Of Poly-protection And The Rationality Evaluation Of The Coal Mining And Excavation Deployment

Gas control is a key problem restricting safe,efficient and green coal mining in China,and multiple protection mining is an important means to eliminate outburst in outburst coal seam mining.The problem of gas control can be carried on smoothly with the reasonable arrangement of time and space for the extraction,driving and mining of the mine.However,the research on the mechanism of damage seepage in coal and rock under multiple protection is not deep enough,and there are few studies on the rational deployment of outburst mining.Based on the engineering background in the mining of deeply inclined coal seams group of multiple protection,on the basis of coal and rock damage seepage and restructuring,mainly from the multiple protection of mining mechanics,rock breaking rule,stress and seepage coupling mechanism of coal and rock under cyclic loading,damage and energy dissipation of three-dimensional reconstruction and fractal characteristics,choice of multiple protection of mining sequence and the overburden rock permeability evolution and outburst mines dug by reasonable deployment evaluation model to build an in-depth study and application,etc.The main conclusions are as follows:(1)Under the multiple protection mining of inclined coal seam group,the coal and rock of protected coal seam are affected by cyclic loading and unloading,and the permeability is affected by stress and damage accumulation.The permeability of the loading stage increased in three stages.The sensitivity of permeability to stress decreases with the increase of peak stress and the accumulation of damage in coal sample.Based on Boltzmann function,a variable model of coal sample damage is proposed.Felicity ratio and quiet effect ratio were used to analyze the stress memory characteristics and damage characteristics of raw coal based on acoustic emission information generated by coal infiltration under cyclic load.The cumulative dissipated energy of coal and rock increases exponentially with the axial effective stress.With the application of cyclic loading and unloading,the damping coefficient of coal decreases first and then increases.The damage variable based on dissipated energy can be used to predict the damage of coal samples and is not affected by the stress path.(2)The relationship between permeability and effective stress after peak is negative exponential function in confining pressure unloading process and negative power function in loading process.The permeability stress sensitivity decreases with the increase of confining pressure loading and unloading times.The permeability decreases with the increase of confining pressure as a negative exponential function.The permeability increment of different confining pressure stages presents a nonlinear change with the effective stress,that is,it first increases and then decreases,and the peak value of increment moves backward with the increase of confining pressure loading and unloading times.The residual stress in the post-peak confining pressure loading and unloading mainly comes from the supporting force provided by the friction slip between the fracture surfaces.(3)Through CT reconstruction,the diameter,volume,surface area and spatial position of the three dimensional fracture body of damaged coal and rock were obtained.The diameter distribution of fractures presents two peaks,which are 0.1~0.7mm and 1.0~2mm respectively.The volume is mainly distributed in the range of 0.005~0.04mm3,and the surface area is mainly distributed in the range of 0.1~0.4mm2.From path 1 to 3,the proportion of microfractures in coal and rock mass increases,while the proportion of larger volume fractures decreases.The surface integral form dimension of pore and fracture increases with the increase of the complexity of loading and unloading path in different coal samples.In terms of coal sample type,the fractal dimension of Yuanzhuang coal sample-Pingdingshan coal sample-Shanxi coal sample increases gradually.The volume and diameter distributions have good fractal dimension characteristics,and the fractal dimension increases gradually from path 1 to path 3.The fractal dimension of Yuanzhuang coal sample-Pingdingshan coal sample-Shanxi coal sample increases gradually under each stress path.The spatial distribution of fracture networks of coal samples under different paths has good self-similarity,and the response of coal samples of different coal types to fracture box dimension of different stress paths is different,but the trend is basically the same.(4)The evaluation index system of selecting the first production layer considering safety,technology and economy is put forward,and the evaluation model of selecting the first production layer based on analytic hierarchy process(AHP)and attribute mathematics comprehensive analysis method is established.The rationality evaluation index system of production deployment of outburst mine is put forward,which is composed of two sets of tunneling advance index and regional measure engineering effectiveness index,and the evaluation system based on Bayesian networks is established.The system can systematically diagnose the rationality of each link of the production deployment of the outburst mine,and rate the rationality of the deployment of the extraction and mining of the outburst mine.The sensitivity results show that the amount of developed coal is the most sensitive to the rational mining deployment of nantong coal mine.When the accident is predicted and the cause is diagnosed through the posterior probability budget,it is most likely to be caused by the insufficient amount of developed coal in the absence of other evidence.The research results of this paper have important theoretical and practical guiding significance for the stress osmotic coupling analysis and damage fracture quantization of gas-bearing coal under cyclic load,the rational deployment technology control and evaluation of extraction and mining,and the diagnosis of accident causes.