Study On Coal Wall Failure And Its Control Technology In Fully Mechanized Mining Face With Large Mining Height In Deep Coal Mine

The failure of coal wall in working face is one of the key factors affecting the technical efficiency of large mining height in fully mechanized mining,and the coal wall damage of deep mining height fully mechanized mining face and its Control technology research is of great significance.especially in the trend of deep development of coal seam mining.In this paper,the 3-1 coal seam depth of Hongqinghe Coal Mine is 582.53~872.67m and the recoverable thickness is5.80~8.41m.Based on the theoretical analysis,the Flac3D software is used for numerical simulation to exploit the large mining height fully mechanized mining method.Characteristics of support pressure distribution and plastic zone width in front of working face in deep thick and extra-thick coal seam,influence factors of coal wall destructiveness,initial support force of hydraulic support and horizontal thrust of guarding plate on coal wall stability and control The method of coal wall stability has been studied in depth and the following main conclusions have been obtained:(1)After the coal seam is mined,the original equilibrium stress of the coal wall at the working face is broken and redistributed.According to the position of the peak of the supporting stress,the front of the working surface can be divided into an elastic zone and a limit equilibrium zone.Through theoretical analysis,the formula for estimating the width of the plastic zone is dived.It can be seen from the above formula that the width of the plastic zone of the working face coal wall is proportional to the depth of the coal seam and the height of the coal seam,and is inversely proportional to the force of the support and the friction coefficient between the contact surface of the coal body and the top and bottom plates.In addition,the numerical simulation study was carried out with Flac3D software.The results show that when the buried depth of the coal seam increases from 600m to 900m,the peak value of the supporting pressure in front of the working face increases from 40MPa to 53MPa,and the stress concentration factor decreases from 2.67 to 2.36.The width of the plastic zone of the working face is increased from 6m to 12m.With the increase of the buried depth of the coal seam,the size and range of the supporting pressure in front of the coal wall of the working face are increasing,but the supporting pressure first increases and then decreases,and gradually Stabilize the process of changing at a certain value.Therefore,with the increase of the buried depth of the coal seam,the peak of the supporting pressure and the width of the plastic zone of the working face coal wall increase,but the peak stress concentration factor decreases.(2)The geological and mining technical factors affecting the damage of coal wall are summarized and analyzed.The orthogonal test scheme is designed.The Flac3D software is used for numerical simulation.The damage coefficient of the coal wall is calculated based on the Drucker-Prager criterion.The results show that the buried depth of the coal seam increases and the damage coefficient of the coal wall increases.The distance between the joint force and the coal wall is reduced,the initial support force of the hydraulic support is increased,the mining height is reduced,and the length of the working surface is reduced.The degree of damage of the coal wall,so as to effectively control the gang;whether the coal wall in the working face is damaged or not,determines whether the gang has occurred,and the primary and secondary ordering factors affecting the destructive factors of the coal wall are:burial depth>joint force point The distance between the coal wall>the initial support force of the hydraulic support>the height of the mining>the length of the working face,it can be seen from this sorting that the artificially adjusted joint force point to the coal wall distance,the initial support force and the length of the working face can reduce the coal wall The extent of the damage.The reasonable process parameters of mining the 3-1 coal seam by the large mining height fully mechanized mining method in Hongqinghe Coal Mine are:the distance from the joint force point to the coal wall is 2m,the initial support force of the hydraulic support is 12000kN,and the working face length is 225m.(3)By establishing the mechanical model and numerical simulation,the influence of the initial support force of the hydraulic support and the horizontal thrust of the guard plate on the stability of the coal wall of the working face is studied.It shows that the initial support force of the support increases from8000kN to 12000kN,and the front of the coal wall The peak value of vertical stress is reduced from 44 MPa to 40 MPa,but the peak-to-coal distance does not change much,about 7 m,and the damage area of the coal body in front of the coal wall is reduced from 13.95 m~2 to 7.44 m~2;When the horizontal thrust is increased from 100kN to 500kN,the horizontal displacement of the coal wall is reduced from 0.47m to 0.28m.At the same time,the damage area of the coal body in front of the coal wall is reduced from 7.75m~2 to 4.65m~2.Therefore,increasing the initial support force of the hydraulic support and the horizontal thrust of the guard plate is beneficial to maintaining the stability of the coal wall,thereby reducing the chance of forming a chip.When using large mining height fully mechanized mining for thick and extra-thick coal seams,the control methods of the working face coal wall are:improving the initial support force and working resistance of the hydraulic support,increasing the support force and support area of the guard plate,and accelerating the working face.Speed of advancement and improvement of the strength of the working face coal.