Study On Mining Roadway Layout And Supporting Technology Of Underlying Coal Seam Of Gradual Separation Layer In Shallow Buried Very Close Distance Coal Seam

With the expansion of coal mining intensity and scale in China,most of the coal seams with relatively simple occurrence conditions have been developed and utilized,while the coal resources with complex mining conditions such as（extremely）close distance coal seams（groups）are mostly mined before and after the mine is closed due to technical and economic benefits.The characteristics of mining pressure behavior in close-distance coal seam mining are obviously different from those in single coal seam mining.Especially affected by the concentrated stress of the coal pillar left over from the upper coal seam,the mining pressure behavior of the mining roadway in the lower coal seam working face is severe,the surrounding rock deformation is large and difficult to control,and it is easy to appear spalling and roof fall accidents,which seriously threatens the efficient and safe production of the mine.Therefore,this thesis adopts the research methods of field investigation,numerical simulation,theoretical analysis and field test to carry out the research on the layout and support technology of the mining roadway under the gradual interval layer of extremely close thin coal seam,which provides a new idea and technical support for the mining of close coal seam.This thesis takes the 317 auxiliary transportation gateway of 6-2 lower coal seam in Hongjingta No.1 Coal Mine as the engineering background.The distance between6-2 lower coal seam and 6-2 middle coal seam is 0.2～3.0 m,which belongs to the typical extremely close distance gradual interval layer condition.Based on this,the FLAC^3D numerical model is established to study the stress distribution law of the underlying coal seam under the gradual interval layer of extremely close thin coal seam.The stress distribution of 6-2 lower coal seam is particularly affected by the concentrated stress of the remaining coal pillars in 6-2,and the smaller the distance between the two coal seams,the stronger the influence of mining stress distribution.Through theoretical analysis,the stress distribution equation of underlying coal seam in close distance is obtained,and the complex stress distribution law of underlying coal seam in close distance is analyzed.The influence of residual coal pillar size,lateral failure depth,mining stress concentration factor and goaf width on the stress distribution characteristics of underlying coal seam in close distance is discussed.Revealed the instability mechanism of surrounding rock of mining roadway under extremely close distance thin coal seam gradual interval layer;considering the failure characteristics of roadway surrounding rock and the self-bearing characteristics of surrounding rock,the idea of controlling the surrounding rock of the mining roadway under the gradual change interval layer of extremely close thin coal seam is put forward.The reasonable position of the mining roadway under the gradual change interval layer of extremely close thin coal seam is studied,and the failure law of the surrounding rock of the mining roadway under different interval layers is analyzed.The technical scheme of active and passive combined support of’bolt+steel mesh+I-steel shed’for the mining roadway under the gradual change interval layer of extremely close thin coal seam is determined.The support effect of the mining roadway under different interval layers is evaluated by numerical simulation,and the field test is carried out in the 317 auxiliary transportation channel of 6-2 lower coal seam.The results show that the surrounding rock control effect of the combined support scheme with’I-steel shed’passive support as the main support and’bolt+steel mesh’active support as the auxiliary support is better,which meets the safe use requirements of the mining roadway under the gradient interval layer of extremely close thin coal seam,and provides a reference for roadway layout and support under similar conditions.