Regularity And Control Of Mining Pressure Induced By Overlying Non-equal Width Coal Pillars In The Mining Process Of Middle Coal Seam With Composite Pillar Residual Areas

In recent years,more and more Chinese coal mines have begun to face complex problems such as depletion of resource reserves,backward production capacity,and prominent safety issues.Recycling of the residual coal has become a powerful measure to expand the coal reserves,improve the recovery rate of resources,and ensure the security of coal resource supply.According to statistics,the reserves of the residual coal seam in the middle of the composite pillar residual mining areas are considerable,and the development potential is huge.However,this type of residual coal seam is usually affected by the backward pillar mining in the upper and lower coal seam.At the same time,the distribution size of the residual coal pillars is different,showing obvious non-equal width feature,which leads to significant differences in the mine pressure behavior,surrounding rock structure and mining feasibility judgment.It severely restricts the safe mining of residual coal seam.Therefore,this thesis chooses the mining of No.10 residual coal seam in the middle of the composite pillar mining areas of Jinhuagong Coal Mine in Datong mining area as the research object,and considers the non-equal width characteristics of the residual coal pillars in the upper No.9 coal seam.By comprehensively using research methods such as field investigation,theoretical analysis,physical model experiment,and numerical simulation experiment,the stability of non-equal width residual coal pillars in the composite pillar mining areas was dynamically analyzed.The stress distribution law of coal and rock layers under different mining conditions was studied.The structure form and stability of the surrounding rock of the stope were revealed.The regularity of mining pressure induced by overlying non-equal width coal pillars in the mining process of middle coal seam with composite pillar residual areas were explained.The recoverability of mining the No.10 residual coal seam in Jinhuagong Coal Mine was discussed,and targeted measures for controlling the strata pressure were proposed.The main research contents and conclusions are as follows:(1)Through the analysis of the stability of the non-equal width residual coal pillars,it is shown that: the stability of the narrow coal pillars is significantly weaker than that of the wide coal pillars.Due to the effect of the composite mining pressure relief effect,the load on the narrow coal pillar is reduced.However,in the mining process of middle coal seam,the leading bearing pressure will be superimposed on the concentrated stress in the residual coal pillars,leading to the instability of the upper narrow coal pillars and strengthening the stress concentration of the wide coal pillars.(2)By studying the evolution law of the surrounding rock stress distribution under different mining states,it is found that: before the mining of the residual coal seam,the stress of coal and rock strata presents the distribution characteristics of "wave state",and the mining stope alternately presents a stress increasing area and a stress decreasing area in the horizontal direction.There is a high stress zone under the overlying wide coal pillar.The residual coal seam corresponding to the narrow coal pillar mining area is under pressure relief.When the coal mining face advances to the area affected by the overlying wide coal pillar,the peak value of the leading bearing pressure increases to 31.67 MPa,which may easily cause strong mining pressure phenomena such as roof fall of the working face,rib fall of coal wall,support safety valve opening frequently and even crushing.It is not conducive to safe production.(3)Under the influence of composite pillar mining,the "residual coal pillar-upper control layer" inverted continuous beam rock mass structure and the "lower bearing layer-residual coal pillar" continuous beam rock mass structure will be formed.At this time,the maximum destruction depth of the upper interlayer rock layer is 0.4 m,and the maximum destruction height of the lower interlayer rock layer is 16.1 m.There is still a complete interlayer rock layer in the stope to ensure the safe mining of the residual coal seam.In the mining process of the middle residual coal seam,the "control layer" structure in the upper interlayer will gradually break and lose stability,especially when passing through wide coal pillars,the cut-out instability will occur,leading to the instability of "residual coal pillar-upper control layer" inverted continuous beam structure,and caused the appearance of strong mine pressure.The "lower bearing layer-residual coal pillar" continuous beam coupling bearing structure can maintain the overall stability during the mining process of middle coal seam,ensuring the safe mining of No.10 residual coal seam in the middle of the composite pillar mining areas of Jinhuagong Coal Mine.(4)Aiming at the appearance of strong rock pressure when the working face is overlying with non-equal width coal pillars,a zoned rock pressure control technology with uniform stress and increased structural stability as the guiding idea is condensed.Specifically: 1)The technical measures for increasing the stability of narrow coal pillars include pillar filling,grouting reinforcement,side wrapping,etc;2)Stress relief measures for wide coal pillars include short-range pressure relief technology and remote pressure relief technology;3)The technical measures that can be implemented in the dangerous area of the stope are mainly the strengthening of the working face support and the filling technology while mining.