Sustainable Mining and Metallurgy

The paper is aimed at the problem of impact dynamic disasters caused by stress concentration ahead of the working face in mining. The universal axial and vertical stress distribution patterns in the mining space were studied through numerical simulations. The plastic damage mechanism of surrounding rock due to the action of nonuniform stress field was theoretically analyzed. The extension characteristics of the plastic zone of the surrounding rock under sustained stress field evolution were obtained. The mechanism of the butterflydegradation trend of the plastic zone of the surrounding rock ahead of the working face under the effect of largediameter unloading boreholes was explained. The results show that when the advancing length is greater than two square, the stress around the goaf tends to be stable, and the minimum principal stress P₃ along the goaf is affected by stress unloading, and there is an inflection point at the boundary of the goaf. The maximum principal stress P₁ increases sharply within 30m in the vertical goaf, and the significant influence distance can reach 90m. The confining pressure ratio changes obviously within 10m in the goaf, the axial lateral pressure coefficient changes more stably, and the vertical lateral coefficient fluctuates greatly near the goaf. The surrounding rock of the hole shows RPP expansion characteristics in the nonisostatic stress field, that is, when the confining pressure ratio continues to increase, the plastic zone of the surrounding rock of the hole will appear the evolution law of circularellipticalbutterfly shape, and its sensitivity is more and more intense and finally shows plastic deterioration, surrounding rock instability, energy release, which explains the pressure relief mechanism of large diameter borehole in front of the working face.Based on the above research, the layout parameters of largediameter boreholes ahead of the working face in a certain mine were designed with a borehole diameter of 600mm and a spacing of 7.5m. After onsite application, monitoring points were respectively set up in the working face and roadway for electromagnetic monitoring. The monitoring results showed a weaker pressure ahead of the working face and a significant effect of the unloading boreholes.