Study On The Failure Law And Control Of Surrounding Rock Of Withdrawal Passage Under Close Goaf

Shendong mining area is one of the modern coal production bases in China,and it is also a typical mining area of shallow buried and short distance coal seam group in China.It is mainly mined by the following line,and roof cutting and support pressing’s accidents often occur in the stage of end mining and withdrawal of working face.Therefore,this paper takes 3304 fully mechanized working face of Hanjiawan coal mine as the engineering background,and adopts physical similar simulation,numerical simulation,theoretical analysis and field measurement and other research means.Meanwhile,this thesis fully analyzes about the working face in retreat in mining through at the end of the channel of basic roof caving characteristic and the instability of solid rock deformation characteristics,and reasonable surrounding rock control technology scheme is put forward.The field investigation shows that the deformation of surrounding rock is positively related to the distance between the working face and the withdrawal channel,and the mutation position of the roof pressure of the withdrawal channel is about 20m away from the working face,and the maximum of the roof pressure is about 15m away from the working face it is connected with the withdrawal channel.Through physical similarity simulation experiment,it is concluded that there are three areas of weighting in 3-1 coal seam working face at the end of mining,namely "stable area","transition area" and "weighting area",and the resistance of working face and support of withdrawal channel in the latter two areas is gradually increasing.When the working face of 3-1 coal seam is connected with the withdrawal channel,the unstable bearing structure of the overlying goaf of 2-2 coal seam appears instantaneous instability,resulting in the deformation and failure of the surrounding rock of the withdrawal channel.The numerical simulation analysis shows that when the overburden fracture of 3-1 coal seam runs through the goaf of 2-2 coal seam at the end of mining,the bearing structure is prone to slide and instability,and the deformation and damage of surrounding rock of the withdrawal channel are aggravated.Through forced roof caving at 5m from the working face to the withdrawal channel,the deformation of the surrounding rock of the withdrawal channel is the smallest,and the mine pressure is relieved,which can effectively control the deformation and failure of the surrounding rock of the withdrawal channel.The theoretical analysis also shows that the mining fracture zone of the lower coal seam runs through the overlying goaf,which makes the unstable dynamic load layer act on the roof of the withdrawal channel,resulting in the increase of roof subsidence and the spalling of side wall.According to the previous research results and the actual situation of the adjacent working face,the measures of presplitting roof of shaped charge blasting and optimizing the support parameters of the retreating passage are proposed to ensure the safety of the retreating work of the working face before the connection of the working face.The engineering practice of 3401 working face shows that after taking blasting measures and optimizing support parameters,the average weighting step,weighting strength and dynamic load coefficient of the working face are greatly reduced,which ensures the safe withdrawal of the working face.