Research on optimization of extraction pipeline connection mode of replacing roadway with borehole in top coal caving face

In order to solve the problem of gas management in upper corner of caving coal face during production,a method of replacing connecting roadway with large diameter drilling hole is proposed to extract gas in the corner of caving coal face.Fluent software is used to simulate the distribution rule of gas concentration in goaf under natural conditions and the influence of different pipeline connection methods on the distribution rule of gas concentration in goaf of No.2-105 top coal caving face of Tenghui Coal Industry,so as to determine the reasonable connection mode of extraction pipeline.The simulation results show that the large diameter horizontal drilling can replace the contact roadway to control the gas problem in the corner of the working face of the top coal caving with high gas content.The gas concentration in the upper corner is 0.25% when the drainage pipe is connected with double hole and double pipe,and the gas drainage effect is the best.The field application results show that the maximum value of extraction purity of 1～6 groups of large-diameter boreholes is 1.05,1.11,1.03,1.06,1.08 and 1.04 m3/min,respectively,which meet the expected requirements of tenghui Coal Industry on gas management in upper corner.In the process of large diameter drilling,the gas concentration in the upper corner is all within controllable range.The gas concentration in the upper corner is 0.32%～0.74%.When the drilling is 20～25 m away from the working face,the gas concentration in the upper corner is in the weak period of controlling the upper corner by large diameter drilling.The technique of "replacing the roadway with the hole" can effectively solve the difficult problem of gas management in high gas caving coal face.