Gas Migration Law And Prevention Technology In Hard And Extra Thick Roof Coal Seam

The No.3-5 coal seam of the Carboniferous main mining in Datong mining area belongs to the extra—thick coal seam.Due to the large thickness of the mining coal seam and the wide range of mining influence,the harmful gas in the goaf migrates to the working face,resulting in the hidden danger of gas overrun in the working face.Gas disasters occur repeatedly in the Carboniferous working face of Datong mining area.Therefore,this paper makes an in—depth study on the gas migration law and prevention technology of extra—thick coal seam.Based on the theory of key strata and the theory of material mechanics,the theoretical analysis of the development process and development height of overburden failure is carried out.Combined with UDEC numerical simulation method,the height and failure characteristics of the three zones of overburden in 8207 working face are determined.The development height of overburden caving zone is 31 m,and the development height of fracture zone is 90 m.Based on the porosity distribution equation of goaf and the characteristics of gas migration,the law of gas migration in stope is analyzed,and the rationality of gas migration law is verified by field measurement.The gas migration law of 8207 working face was analyzed by Fluent simulation software.The results show that the 8207 working face in the use of one into a return ventilation mode,the upper corner area of gas accumulation,gas concentration can reach 5 %.The gas distribution in the goaf is : in the direction of the goaf,the deeper the goaf,the slighter the air leakage,the higher the gas concentration;in the inclined direction of the goaf,the closer to the return airway,the higher the gas concentration near the return airway due to the air leakage and return of the goaf;in the vertical direction of the goaf,because the gas density is less than the air,the gas moves upward under the action of floating,and the concentration is higher.The vertical distance of 18 m and the horizontal distance of 15 m of the high drainage roadway are determined as the best high drainage roadway orientation by simulation.Under this scheme,the prevention and control effect of gas overrun in the working face is the best.The simulation results show that the maximum gas concentration in the upper corner is only 0.63 %,the maximum gas concentration in the working face is only 0.57 %,and the gas extraction concentration is 3.92 %.Determine 7 k Pa as the best extraction negative pressure,not only can well control the working face,the upper corner gas concentration,and will not be due to excessive air leakage and the risk of spontaneous combustion;the optimal extraction weight range is 0.33 ～ 1.With the aid of mine gas field monitoring data,it is concluded that the average gas concentration in the upper corner of the working face is 0.247 % after using the high drainage roadway as the gas prevention and control technology,and the average gas extraction rate during the pressure period of the working face can reach 80.8 %.it is verified that high drainage roadway can effectively control the gas concentration of working face.By studying the fracture evolution law of 8207 working face and overlying strata,the gas migration law is analyzed,and the gas prevention and control technology of high drainage roadway in extra—thick coal seam with hard roof is established.The application and promotion of research results can provide support for the development of gas prevention and control in similar mining face.