Reasonable Layout And Stability Analysis Of Withdrawal Channel In Layered Working Face Under Extra Thick Coal Seam

For the fully mechanized caving face of extra-thick coal seam,the stability of surrounding rock of the evacuation channel during the final mining determines the removal and evacuation work of the working face and the mining efficiency of the whole mine.In the final mining stage of fully mechanized caving working face,the withdrawal channel is affected by the advance abutment pressure of the working face,and the surrounding rock stress field environment of the working face and the withdrawal channel increases significantly,which leads to the occurrence of large deformation of surrounding rock,induced roof caving,caving,roof pressure frame and other accidents,and seriously affects the smooth progress of the moving and withdrawal work of the working face.Based on the research background of the drawback channel of fully mechanized caving working face under the strata of extra-thick coal seam in Hujitui Well 1-2 of Daliuta Coal Mine,this paper aims at the actual situation of mining in the mined-out area above the strata at the lower strata working face in the process of extra-thick coal seam mining.The drawback channel is affected by multiple stress concentration such as upper layer goaf,upper layer main and auxiliary drawback channel protected coal pillar and working face advanced mining stress superposition disturbance.By field measurement and theoretical analysis,numerical simulation and engineering monitoring comprehensive research method,the system is analyzed to retreat under mined-out area of coal wall rock stress field and plastic zone distribution,obtained during the mining working face advancing at the end of the sync subtalar retreat channel and evolutionary regularity of plastic zone of surrounding rock stress,determine the reasonable decorate,illustrates the key retracement channel coordination control,The cooperative control scheme of roadway surrounding rock stability and its specific parameters are proposed and the application effect is verified.The main conclusions are as follows:(1)The stress distribution and failure characteristics of the coal roadway under the goaf were analyzed,and it was concluded that the failure degree of surrounding rock of the roadway was low and symmetrical when the goaf was arranged in the inner fault area,while the failure degree of surrounding rock of the roadway was serious when the outer fault area was arranged,and the plastic zone was developed significantly above the shoulder Angle.Then,under the action of overlying goaf,the distribution of stress and plastic zone in surrounding rock of the drawback passage is simulated when the drawback passage is arranged in different positions of the lower layer working face.It is preliminarily determined that the failure deformation of surrounding rock of the drawback passage is relatively controllable when the drawback passage is arranged 10 m and 15 m at the boundary of the overlying goaf.(2)Theoretical analysis is made on the ore pressure appearance law of the drawback channel in the final mining process,and the advance abutment pressure moves forward with the advance of the working face.In the early stage of the last mining,the working face is far away from the drawback passage,and the surrounding rock of the drawback passage is not significantly affected by the advance mining of the working face.From the middle to the end of the last mining,with the advance of the working face,the surrounding rock stress of the drawback passage gradually approaches and exceeds the risk judgment line of rock burst which may be dangerous.(3)during the period of mining,at the end of the working face advance,the remaining coal pillar size decreases,retreat channel in different degree of surrounding rock stress,to breakthrough,its surrounding rock stress peak value increases obviously,and through the contrast analysis retreat channel layout in mined-out area boundary 10 m wrong when retreat channel environment is low and relatively stable,surrounding rock stress field is beneficial to control the surrounding rock.(4)Comparative analysis shows that the plastic failure range of surrounding rock of the working face and the drawback channel in the final mining process is relatively small and the bearing structure is relatively stable when the drawback channel is arranged at 10 m at the boundary of the outer fault goaf.Therefore,the evacuation roadway along the bottom excavation is selected at 10 m in the outer fault goaf,and the evacuation auxiliary roadway is arranged at a horizontal distance of 30 m from the evacuation channel.(5)During the final mining period,with the advance of the working face,the plastic zone extension range and extension depth of surrounding rock around the drawback channel increase to varying degrees.When the working face and drawback channel are connected,the plastic damage of surrounding rock around the working face and drawback channel is serious,and the bearing structure is damaged.According to the distribution pattern of surrounding rock plastic zone in the final mining process when the drawback passage is arranged at 10 m boundary of the outer fault goaf,it can be concluded that the plastic zone of surrounding rock in the drawback passage presents obvious asymmetric distribution,and the remaining coal pillar in front of the working face and the top corner of coal pillar in the section of the drawback passage should be the main control part of surrounding rock control.(6)According to the failure characteristics and distribution of surrounding rock of the drawback channel during the final mining period,the coordinated control scheme and specific parameters of supporting(anchor cable + net + steel belt)and modification(grouting reinforcement)for the drawback channel are determined.Field of surrounding rock stability of the proposed control scheme for the application,working face and retreat channel displacement monitoring section monitoring results show that the displacement deformation of each measuring point are less than 300 mm,end face and retreat channel at the end of the surrounding rock deformation stability,ensure the fully mechanized equipment safety after rapid retreat,at the end of the working face work move smoothly.