A calculation method of reasonable size of coal pillar in large mining height section based on elastic theory

There are significant differences in abutment pressure distribution and rock mass deformation on both sides of section coal pillar under different working conditions, the influence of different abutment pressures on the overall stability of coal pillar is considered, based on the elastic mechanics calculation model of coal pillar in large mining height section, the stress-strain components of any unit rock mass of coal pillar under abutment pressure are analyzed. Through the establishment of large mining height pillar elastic-plastic interface on the rock column model, it is determined that unit rock mass will first undergo horizontal tensile failure at 0.65 times the height of coal pillar, based on Hooke's law, the relationship between the ultimate stretching strain of rock mass and the width of limit equilibrium zone of coal pillar is proposed. According to the mechanical characteristics of the rock mass in the coal pillar fracture zone, the calculation formula of the width of the coal pillar fracture zone is derived by using the Mohr-Coulomb criterion. The results show that: ①The width of limit equilibrium zone of coal pillar is inversely related to ultimate tensile strain and elastic modulus of rock mass and positively related to buried depth and height of coal pillar;②The height of coal pillar and the interface friction angle between coal pillar and roof and floor are the key factors affecting the width of fracture zone; ③Under different working conditions on both sides of coal pillar, due to the positive relationship between the ultimate tensile strain of coal pillar rock mass and its lateral pressure, the lateral pressure on the gob side of the section coal pillar is larger than that on the roadway side, and the ultimate tensile strain of the rock mass on the gob side is correspondingly larger, which shows that the width of the limit equilibrium area on the gob side is smaller than that on the side of the gateway. Finally, the above theoretical formula is applied to the analysis and calculation of the width of limit equilibrium zone and fracture zone of coal pillar in large mining height section of 30109 working face in a mine in Northern Shaanxi, and the reasonable width of coal pillar and its supporting scheme under different working conditions on both sides of the working face are given. The engineering application shows that the deformation control effect of surrounding rock along the working face is good, which can meet the demand of field production.