Study On Arrangement Of High-level Borehole For Gas Extraction In Pressure Releasing Area Based On The Rule Of Mining Fissure Growth

During the stoping of mining,the mining fissure formation and expansion of the overburden are influenced by the mine mining,and the gas passes through the mining fissure to the upper corner and the return airway,which causes the gas concentration exceeding the limit,and restricts the safe and efficient mining of the mine.In this dissertation,physical similarity simulation experiment,FLAC3D numerical simulation experiment,theoretical analysis and field engineering verification are used to study systematically the development rule of mining fissure growth and the circulation channels of pressure relief gas in the 20102 working face of Shennanwa coal mine and determine the layout scheme of high-level borehole for gas extraction.The results of the study show that:The relative gas gushing quantity of the working face is 11.76m3/t and the absolute gas gushing quantity is 22.87m3/min.It is necessary to establish the gas extraction system.It is appropriate to adopt high-level borehole drilling to extract gas and solve the problem of gas concentration exceeding the limit in the upper corner and the return airway during the stoping.The first weighting interval is 46m,the periodic weighting length is 14-22m,and the periodic weighting length averages is 17.33m.The comprehensive gas extraction effect and the periodic weighting length determine that the drilling interval is 21m.Through the analysis of abutment pressure,the joint position of the working face and the goaf is the stress concentration zone(the width is 16-22m).The fracture area is arched and located at the upper part of the stress concentration area,which is the key area of gas extraction.Combining the height of fractured zone and the location of borehole,the final hole position is determined to be 39 meters away from the return airway.During the stoping of the working face,it is within the 45m range of the 2#coal seam,which is the fracture development and the key area of gasextraction.Considering the height of the three zones(the caving zone distance to the 2#coal seam 16-20m,the fracture zone distance to the 2#coal seam 68-78m,the bending zone to the surface),the development area of fissure and the requirements of drilling construction,the final hole location is distance to the 2#coal seam 25-30m.By analyzing the experimental borehole gas extraction effect and borehole gas extraction flow field,the diameter of drilling hole is 153mm and the spacing between holes is 2m.Through borehole televiewer to observe the development of roof fissures determine the vertical length of casing reinforcement from 2#coal seam 7m.Based on the borehole layout parameters,we can know the effect of gas extraction.When the mine does not extract gas,the maximum concentration of the upper corner gas is 1.41%,the average concentration is 1.1%,the maximum concentration of the return airway is 1.1%,the average is 0.95%.When the gas is extracted from the mine,the maximum gas concentration in the upper corner is 0.76%,the average is 0.57%,and the maximum concentration of gas in the return airway is 0.78%,the average is 0.63%.The gas extraction effect is remarkable,which reduces the gas concentration in the upper corner and the return airway,and ensures the safe and efficient mining of the mine.