Distribution characteristics of"three-zone"in Bofang Coal Mine goaf and its application in high and long drilling extraction
In order to improve the efficiency of goaf gas extraction in No.3305 working face of Bofang Coal Mine,the evolution law of over-lying rock caving and fractures at different advancing distances of the working face was analyzed through numerical simulation,and then to determine the height of the"three-zone"of the No.3305 working face.Furthermore,the height of the"three-zone"in the goaf of the No.3305 working face was determined.Finally,the selection of directional high-level long borehole layout layers were analyzed,and the extrac-tion effect of directional high-level long boreholes was investigated in the No.3305 working face.The results of this study indicated that the maximum height of overlying rock caving zone on the No.3305 working face of Bofang Coal Mine are 17.5 m,while the maximum height of the caving zone is 56 m.The gas extraction amount of the directional high-level long borehole ranges from 2.06～11.09 m3/min,and the gas extraction concentration maintains at a high level,with an average concentration of 44％.It shows that the final hole of the high-level long borehole is located in the middle and lower part of the fracture zone,which can effectively extract the gas in the goaf.
gas extractionlong borehole"three-zone"goaffracture
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