Study On Evolution Law Of Overburden Fractures And Gas Control In 209 Working Face Of Huangling No.2 Coal Mine

Gas hidden dangers generally exist in the process of coal mining in Huangling mining area.Due to the unreasonable design parameters of gas drainage,the gas drainage capacity of some mines is low and the effect of gas control is poor.It is of great theoretical and practical significance to study the fracture evolution law of the overlying strata of the working face and determine the reasonable drainage position for accurate gas drainage.Taking 209 working face of Huangling No.2 coal mine as the object,this paper studies the fracture evolution law of overlying strata in the mining process of 209 working face by using the method of numerical simulation and on-site microseismic monitoring,and then judges the spatial position of fracture zone,so as to provide a scientific basis for gas drainage design and gas control in goaf and high fracture zone of this working face.It is found that during the advancement of the working face,the overburden in the goaf along the strike produces a pressure relief zone,and the stress gradient gradually increases from the inside to the outside and from the center to the periphery.With the advance of the working face,the range and height of the full pressure relief area gradually increase,and the height finally stabilizes at about 70m away from the coal seam.Along the strike,the overburden in front of the working face forms a pressure relief area,a stress rise area an d an original rock stress area.Microseismic monitoring shows that in the initial stage of periodic roof pressure,the roof cracks in goaf begin to breed,produce and expand,and are mainly longitudinal cracks;With the advance of the working face,new fractures are continuously generated in the middle and lower roof of the goaf and connected with the original fractures to form a roof fracture zone.The fracture development height is between 60-80m,and the average height of the fracture zone is about 70m;After the cracks in the lower roof of the goaf are connected,a large range of collapse occurs,and the upper roof is separated.So far,the one-time periodic pressure is basically formed.During the on-site monitoring period,a total of 7 periodic incoming pressures were generated,and the average step distance of periodic incoming pressure was about 20m.According to the results of numerical simulation and microseismic field monitoring,the high-level borehole is optimized,the gas drainage effect of working face 209 is significantly improved,and the safe and efficient mining of working face is ensured.