Study On Reasonable Size Of Coal Pillar In Fully Mechanized Mining Face With Large Mining Height Under Repeated Disturbance

With the rapid development of coal mining technology in China,the comprehensive mechanized mining technology with large mining height has become the main development direction of medium-thick coal seam mining.In order to ensure the safe and efficient mining of large mining height face and improve the recovery rate,it is of great practical significance to study the reasonable width of section coal pillar under the condition of repeated disturbance.Due to the objective difference of the mechanical conditions of the coal pillar between the tunneling period and the mining stage,there will be different reasonable widths for the coal pillar to remain stable in different stages.In view of the fact that the existing calculation theory of coal pillar width ignores the influence of one side of coal pillar on the abutment pressure of the other side during secondary mining,and it is difficult to quantitatively analyze the influence of caving rock mass on the stability of coal pillar.In order to ensure the safety and stability of coal pillar during tunneling,especially during mining,this paper takes 30109 working face of a mine in northern Shaanxi as the engineering background.in this paper,the reasonable width of coal pillar in 30109 working face of this mine at different stages is studied Systematic by means of laboratory test,theoretical analysis and numerical simulation.The main conclusions are as follows:(1)The section coal pillar needs to go through three stages:trench excavation,primary mining and secondary mining.In different stages,the coal pillar will be affected by different degrees of disturbance,and show different deformation and failure characteristics.The stable state of section coal pillar is closely related to the basic physical and mechanical parameters of coal and rock mass.Through field sampling and laboratory test,the basic physical and mechanical parameters of coal pillar in 30109 working face of a coal mine in northern Shaanxi are obtained.(2)Based on the mechanical model of abutment pressure of coal pillar in large mining height section during tunneling and primary mining,the limit equilibrium zone and fracture zone of coal pillar in the excavation stage are analyzed.Considering the influence of primary mining disturbance,the expanded width of the fracture zone on both sides of the coal pillar is discussed.The results show that after the completion of tunneling along the tunnel,a certain degree of elastic-plastic deformation will occur on both sides of the coal pillar under abutment pressure,and the primary mining will aggravate the plastic failure of the coal pillar rock mass.(3)Considering the influence of abutment pressure on one side of coal pillar on the overall deformation of coal pillar,the force analysis model of section coal pillar under the action of abutment pressure during secondary mining is constructed.The relationship between the width of limit equilibrium zone of coal pillar and the ultimate tensile strain of coal pillar rock mass is analyzed according to Hooke’s law.On this basis,a formula for calculating the reasonable width of coal pillar to keep stable during secondary mining is put forward,and the main factors affecting the width of limit equilibrium zone of coal pillar are analyzed.The results show that the buried depth of coal pillar,elastic modulus of rock,ultimate tensile strain and height of coal pillar have significant influence on the width of limit equilibrium zone of coal pillar.(4)The deformation range of coal pillar in 30109 working face of a coal mine in northern Shaanxi under different stages and widths is simulated by using FLAC3D numerical software.The analysis shows that during the driving along the tunnel,the coal pillar is less affected by the construction disturbance,and its plastic zone,stress and rock mass displacement are not large.During the first mining period,due to the influence of mining,the deformation and destruction of coal pillar is further intensified,and the bearing capacity of coal pillar is lower than that during excavation,but it can remain stable.During the period of secondary mining,the damage degree of coal pillar is the most significant due to the influence of secondary mining.When the width of coal pillar is more than 25m,the coal pillar is in a relatively stable state during excavation and mining,and when the width of coal pillar is less than 25m,the deformation of coal pillar is serious.(5)By using the above theoretical formula,this paper analyzes and calculates the reasonable width of the coal pillar in the 30109 working face of a coal mine in northern Shaanxi,which is stable in different stages,and determines that the reasonable width of the coal pillar in this working face is 19.1 m.Considering the safety and stability of coal pillar during mining,the reasonable width of coal pillar is determined to be 25m,and a reasonable support scheme is given.The field monitoring results show that the deformation control effect on both sides of coal pillar in 30109 working face is good,which can meet the needs of on-site production.