Study On Permeability Evolution Characteristics Of Pressure-Relief Coal-Rock Mass In Protective Seam Mining

With the increase of mining depth and mining intensity,resulting in the condition of mining tends to be complicated,and appeared the characteristics of "three high and two low",which made it is possibility of coal mine gas accident is greatly improved in high gas mine.Therefore,Based on the study on permeability evolution characteristics of pressure-relief coal-rock mass in protective seam mining,it can provide some theoretical and technical support for the coal mine safety,efficient exploitation and efficient extraction and utilization of gas resources.The paper uses the methods of theoretical analysis,statistical analysis,experimental research and numerical simulation,that systematically analysis the characteristics of pressure relief,deformation characteristics and the gas flow law of protected seam.In this paper,the data of mining practice of the lower protective layer in 16 mines are analyzed,and the functional relationship between the protective layer and the protective effect is established.According to the different forms of gas flow in coal and rock mass,based on the Klinkenberg effect,the mathematical model of gas fluid solid coupling of coal seam rock mass is developed.The Changping Mine protection layer mining control 3#coal seam gas disaster as engineering background,the numerical simulation and similarity simulation experiments are carried out.The research results show that the relationship between the increase of the permeability coefficient of the protected layer and the decrease rate of the original rock stress and the variation of the relative layer spacing are respectively quadratic polynomial,which in the case of the mining height is 1.5m,2.0m and 3.0m.Through theoretical calculation,numerical simulation and similarity simulation experiment,it is found that the dynamic evolution curvature of the volume deformation of protected seam in the protective layer mining is "M" type,and the permeability process of dynamic evolution has undergone a process of decreasing,increasing,decreasing and finally stabilizing.Among them,the simulation experiment with the working face advancing,the maximum protection layer volume strain rate and permeability increasing ratio is 7.7‰ and 17.8 times,compared with the results of numerical simulation and theory(respectively 7.5%and 500 times?800 times)it had decrease one magnitude order It is shown that the analysis results of two-dimensional similarity simulation experiments have some limitations,based on this,this paper presents the design scheme of the three-dimensional simulation test system for the seepage characteristics of coal and rock mass,and this system has 5 parts mainly comprises a box body sealing system,pressure loading and control system,constant pressure gas loading and flow monitoring system,simulation of recovery layer and mining stress strain monitoring system.