Discussion on determination method of the limit equilibrium zone width based on the deformation analysis of coal wall

The redistribution of the stress in surrounding rock will generally occur after the excavation of the mining roadway. The coal mass deforms under the action of upper concentrated stress and the limit equilibrium zone within the coal-side,whose theoretical width is an important basis for reasonably determining the support scheme and parameters. At present,the width of the limit equilibrium zone is solved according to the stress equilibrium differential equation of the coal-wall based on the stress medium equilibrium theory of loosed material or the width equation about the limit equilibrium zone by the nonlinear Mohr-Coulomb criterion considering the engineering disturbance level and geolog- ical strength of coal body. Summarizing the existing research methods on the limit equilibrium zone,this paper established the mechanical calculation model of the coal-side under high bearing pressure,and the stress-strain components of the coal body within the coal-side were analyzed using the theory of elasticity mechanics. The unit coal body with the maximum horizontal tension strain under the action of peak bearing pressure was located at the 0. 65 times height of roadway,which was determined by the vertical slice model of the coal body at elastic-plastic interface. Then the the- oretical formula connecting the ultimate tensile strain of the coal body with the limit equilibrium zone width was put forward. The analysis shows that the width of the limit equilibrium zone of the coal-wall is dependent on the parameters of the coal mass such as ultimate tensile strain,Poisson’ s ratio,elastic modulus,primary rock stress,the maximum bearing pressure as well as the elastic zone width of the coal-wall. Specifically,the width of the limit equilibrium zone of coal-wall increases with the buried depth addition of the roadway,but decreases rapidly with the increase of the e- lastic modulus of the coal as well as its ultimate tensile strain. On this basis,the limit equilibrium zone and the width of the failure zone of the coal-wall in the 350-400 m section of the transport roadway in 14501 mining face of Bailiang Coal Mine were calculated by the proposed theoretical formulas,and the bolt support parameters of the coal-wall were optimized,and some good supporting effects were obtained. The above research can be used to predict and analyze the limit equilibrium zone of the coal-wall in deep buried seam roadway.