Study On Small Pillar Of Gob-Side Entry Driving Under The Jurassic Coal Pillar In Extremely Thick Coal Seam Top Coal Caving Longwall Mining Of Tongxin Mine

For a long time,due to the mining of double-system coal seam,the strong mine pressure problem of carboniferous system working face and roadway by Jurassic residual coal pillar is one of the main factors affecting the safe and efficient production of Tongxin Coal Mine.Through theoretical analysis,numerical simulation and field measurement,the influence of Jurassic coal pillar on working face and roadway with large coal pillar of carboniferous was studied,the influence mechanism of the Jurassic coal pillars was revealed,the reasonable width of coal pillar was determined,and the influence degree of residual coal pillar on small coal pillar roadway was investigated.A reasonable scheme of roadway support was proposed through simulation analysis,and has obtained the good result in the industrial experiment.The main research results are as follows:There is stress concentration exist in Jurassic residual coal pillar coal pillar,and the working face and the roadway of large coal pillar of carboniferous system are greatly affected by the residual coal pillar.The stress concentration of large pillar roadway is caused by the superposition of three kinds of stress,that is,the front stress of the working face,the lateral abutment pressure of gob and the concentrated stress transferred from Jurassic coal pillar.The development height of working face roof fracture zone affects the stress concentration area under Jurassic pillar,making the stabilized Jurassic gob and the residual pillar structure unstable.the high elastic energy that accumulates in the affected area is released suddenly,which causes the influence of the remaining coal pillar on the working face of the carboniferous to change from the distribution of the concentrated stress field over a large area becomes the downward concentrated load,and finally leads to the pressure significant increase of working face and roadway during crossing the coal pillar.The range of the reduction area of lateral abutment pressure after the stability of8307 gob is 0m to 12.77 m,and the width of coal pillar in 5305 roadway is 6m.The small pillar is not affected by the coal pillar during the tunneling,and is still affected during the mining which has a smaller influence than the lager coal pillar roadway.The results show that the use of small coal pillars along the empty roadway can effectively reduce the risk of strong pressure when the carboniferous roadway passes the Jurassic coal pillars.By simulating different support parameters,the support form of coal pillar influence zone in 5305 roadway is determined,and the deformation degree of roadway during under the two conditions of "6m small coal pillar roadway + reasonable support" and "38m large coal pillar roadway + original support of Tongxin Coal Mine" is compared and analyzed.The results show that 6m small coal pillar combined with reasonable support form can effectively improve the serious problem of roadway deformation in the past period when the large coal pillar roadway passed the Jurassic coal pillar with Tongxin Coal Mine.The field measurement data shows that the scientific coal pillar width,reasonable roadway support parameter and corresponding control measures of roadway surrounding rock make the working face in the process of mining without strong pressure behavior,Roadway deformation is maintained within a controllable range,which ensures the safety and smooth production of the working face.