Study on the influence of coal pillar left by long-distance mining of protected layer on the mining of protected layer

In order to study the influence of the coal pillar left over from the mining of the protective layer over a long distance on the mining effect of the protected layer, the coal pillar and Ⅳ_5-6-22190 working face of the section with a remaining width of 4 m between Ⅴ₈-22310 machine lane and Ⅴ₈-32010 air lane of Ⅴ₈ coal seam in Pingdingshan No.6 mine are taken as the research object, by means of theoretical analysis, numerical simulation and field measurement, the influence range of coal pillar, the distribution of vertical stress in coal pillar region and the variation law of related parameters in the influence region are studied. The results show that the influence range of 4 m wide residual coal pillar is 27.3 m, the ultimate strength is 25.9 MPa, the plastic zone width is 2.26 m, and the elastic zone width is 2.68 m. When the working faces on both sides of the coal pillar are mined, the maximum vertical stress of the coal pillar is 87.9MPa, which far exceeds the load limit of the coal pillar itself; there is no obvious difference between the residual gas content and pressure measured in the coal pillar influence area and the pressure relief protection area, and they are all less than the critical value of outburst danger, and the gas is released well in the coal pillar influence area; there is no obvious stress concentration phenomenon in the influence range of the coal pillar, the small coal pillar left behind has little influence on the protected effect, the protection effect has continuity in trend, and the influence on the working face of the protected layer is little.