Research On Protective Range And Protective Effect Of Stress Concentration Area Of Remaining Coal Pillar Mined By Short-range Protective Layer In Xinjing Mine

In order to study the influence of the residual coal pillar stress concentration zone on the protection scope and protection effect of the protected layer,the mining background of Xinjing Coal Mine's short-range protective layer is used as the engineering background,and the theoretical analysis of protective layer mining and elastoplastic mechanics is adopted.Research methods combining mechanical analysis,numerical analysis and field investigation,the research on the protection scope and protection effect of the protected coal layer stress concentration area of the coal pillars mined by the protective layer of the coal mine was launched,the research content has important guiding significance for the prediction and prevention of coal and gas outburst disasters.Here are the main research results:?1?By studying the formation and distribution of"three horizontal zones,three vertical zones"in the overburden damage caused by close-protection mining,the data of the mine fall zone and fissure zone height are calculated,and the maximum heights of the fall zone and fissure zone are respectively Approx.6.3m and 16.7m?±4m?.?2?Based on the theory of protective layer mining,first construct a mechanical model of the protective layer,obtain the mechanical calculation formula of the protective layer,determine the basis for determining the impact danger of the protective layer,and after repeated consideration and formula calculation,the maximum principal stress of the coal body is 24 MPa.It does not constitute a mechanical condition for impact;after the maximum principal stress is known,the protection range is combined with relevant parameters of the coal pillars to conduct further research and calculation.The corresponding pressure angles of the remaining coal pillars to the 9th coal seam after the mining of the 8th coal seam are obtained The value of?₃ is 75°,and the corresponding pressure angle?₅ along the strike direction is 60°.Then the calculated value is 7.1m at the start line and stop line and 5.5m at the coal pillar.The stress concentration area is determined below the coal pillar.?3?Based on the engineering geological conditions of Yangjing Xinjing Mine,FLAC3D was used to simulate the overburden stress change,vertical displacement,and distribution of plastic zones during the mining of No.8 seam.When the mining is completed,the vertical stress state is centered on the remaining coal pillars,and it spreads symmetrically to both sides in turn.The farther away from the remaining coal pillars,the larger the diffusion range.The influence range of the remaining coal pillars is 33m,and the maximum vertical stress value is 38.6MPa.With the increase of the depth of the remaining coal pillars,the maximum value of stress transmission to the protected layer of No.9 coal seam is 22.5 MPa,a reduction of 41%.?4?Through the field survey and analysis of the basic parameters such as the gas pressure,gas content,permeability coefficient,and cuttings gas desorption index of the protected layer of No.9 coal seam before and after mining of the protective layer of No.8 coal seam in Xinjing Mine of Yangmei Coal Mine The research results found that the maximum gas pressure of No.9 coal seam decreased from 1.37 MPa to 0.15 MPa,a decrease of 89%;the gas content of No.9 coal seam decreased from 11.17 m³/t to 5.90 m³/t,a decrease of 47%;The permeability coefficient has increased by 16 to 225 times;the K₁ value of the cuttings gas desorption index,the S value of the cuttings volume and the stress distribution state have a good correlation.At the same time,it is concluded that the coal seam gas can be fully released in the case of close protection layer mining..