Research On Deformation And Failure Characteristics Of Coal Seam Above The Complex Goaf In Qianjiaying Mine

Qianjiaying Coal Mine in Kailuan mining area,due to the problem of mining connection,the lower coal seam is mined first and then the upper coal seam is mined.The 1359 W working face studied in this paper is located in 5 coal seam,and there are 3 goafs in 7 coal seam below,forming2 coal pillars,one of which is the goaf of 9 coal seam,Due to the problem of mining system,the layout of mining roadway in No.5 coal seam can only intersect with the mining roadway in the underlying coal seam at a nearly vertical angle.The influence of the underlying goaf on No.5 coal seam is more complex.It is of great significance for the safety of 1359 W working face to study the influence of underlying goaf on coal seam 5.In this paper,theoretical analysis combined with numerical simulation is used to analyze the deformation and stress of coal seam 5 affected by the mining of coal seam 7 and 9 below,so as to judge the mining feasibility of 1359 W working face.Three dimensional laser scanner was used to measure the deformation of No.5 coal seam and the roadway deformation of 1359 W working face.Finally,the mine pressure behavior in the mining process is analyzed,and the working resistance of the hydraulic support in the working face is recorded.The research results show that 1359 W working face is located in the upper part of the fracture zone in the goaf of the underlying coal seam.After a long time,the 5 coal seam is stabilized again.The maximum deformation of the 5coal seam overlying the superimposed area of the goaf of the underlying two coal seams is 2.8 m,and the maximum deformation of the 5 coal seam overlying the goaf of a single coal seam is 1.3m.Taking the roof of transportation roadway as an example,in the monitoring period,more than50% of the roof displacement of the roadway above the coal pillar is 33.6 mm ? 38.9 mm,more than 50% of the roof displacement of the roadway above the goaf is 15.9 mm ? 19.8 mm,more than 50% of the roof displacement of the roadway above the solid coal is about 20 mm,and the roof deformation of the return air roadway also shows similar rules.In the process of working face mining,the stress of the hydraulic support passing through the underlying goaf will increase,but it does not reach the alarm value,and the working resistance of the hydraulic support in other positions is stable.It is concluded that the underlying goaf will cause 5 coal seam undulation,and the support shape should be adjusted properly in the process of mining.The coal pillar between the goafs of the underlying coal seam will accelerate the surrounding rock deformation of the overlying coal seam roadway,and the goaf of the underlying coal seam will produce pressure relief effect on the overlying coal seam,and increase the cracks of the overlying coal seam,The displacement of the individual position of the mining roadway in the overlying coal seam is greater than that of the surrounding rock.In the process of mining,we can strengthen the support for the area above the coal pillar where the roadway is located between the goaf of the underlying coal seam,and the area where the roadway is located above the goaf of the underlying coal seam should take measures to prevent the harm caused by spalling.Overall,1359 W working face can be safely mined.The research results can be used for reference to the upward mining near the working face in the same coal seam.