Mechanism and Technical Application of Danger Elimination in Advance Drilling of Working Face Based on Butterfly Theory
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 non-uniform 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 butterfly-degradation trend of the plastic zone of the surrounding rock ahead of the working face under the effect of large-diameter 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 30 m in the vertical goaf,and the significant influence distance can reach 90 m.The confining pressure ratio changes obviously within 10 m in the goaf,the axial lateral pressure coefficient changes more stably,and the ver-tical lateral coefficient fluctuates greatly near the goaf.The surrounding rock of the hole shows RPP ex-pansion characteristics in the non-isostatic stress field,that is,when the confining pressure ratio contin-ues to increase,the plastic zone of the surrounding rock of the hole will appear the evolution law of circu-lar-elliptical-butterfly shape,and its sensitivity is more and more intense and finally shows plastic deterio-ration,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 large-diameter boreholes ahead of the working face in a certain mine were designed with a borehole diam-eter of 600 mm and a spacing of 7.5 m.After on-site application,monitoring points were respectively set up in the working face and roadway for electromagnetic monitoring.The monitoring results showed a wea-ker pressure ahead of the working face and a significant effect of the unloading boreholes.
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