| Coal is the main energy source in China,but there are more high gas and low permeability coal seams,which leads to frequent gas accidents in the mining process.This paper focuses on the characteristics of mining-induced stress-fissure gas migration in the Ji15 coal seam of the No.8 mine,and its influence mechanism on the gas emission in the Ji16-17 coal seam(the close relief layer).Based on the actual geological conditions of Pingmei No.8 Coal Mine,the distribution characteristics of fracture field in the mining process of Ji 15 coal seam were simulated by using the bidirectional loadable multi-function analog device and 3DEC numerical simulation software.Established considering stress,gas adsorption,desorption,coal mining damage and permeability anisotropy of multi-factor coupling model,the model for calculating by using numerical simulation software COMSOL,studied the first layer of different length of mining,unloading stress change characteristics and simulation to study the initial mining layer after pressure relief mining characteristics of gas migration,and the simulation results to verify each other.The main conclusions are as follows:(1)For eight ore has Ji15 coal seam and leveling has only 4 m Ji16-17 coal seam spacing,considering the Ji15 coal seam in the process of mining floor below the damage degree of rock is larger,and damage to the permeability significantly increased effect should not be ignored,so set up considering gas desorption,coal mining stress,damage and permeability anisotropy of multi-factor coupling model.To improve the accuracy of gas seepage numerical simulation.(2)Based on the similar simulation experiment,the evolution of mining-induced fracture field in Ji15 coal seam shows that the initial compression occurs when the coal seam is mined to 35m,the average compression step distance after that is 16.43m,and the fracture fracture Angle ranges from 32° to 67°.When the working face advanced to 150m,the fractures on both sides developed well and formed a "trapezoidal fracture zone" with the bed-separated fractures on the upper part.The bed-separated fractures in the middle area were compacted and distributed asymmetrically in the annular fracture zone on the open hole cut and the coal pillar side of the working face.(3)The study of stress field variation based on numerical simulation shows that the stress field is always symmetrically distributed along the middle of the goaf during the advance of the working face in the first mining layer,the pressure relief area of coal and rock mass is similar to an ellipse,and the stress concentration phenomenon exists behind the cut hole and in front of the working face.With the continuous advancement of the coal face,the pressure relief range of coal and rock around the goaf increases gradually,and the pressure relief degree and the stress concentration degree at both ends also increase continuously.The full unloading length of the unloading layer is in direct proportion to the advancing distance of the working face.With the increase of the advancing distance of the working face,the full unloading range of the unloading layer can reach about 85%.(4)The simulation analysis of seepage field evolution of adjacent coal seams induced by mining in J15 coal seam of No.8 Mine of Pingmei Coal Mine shows that the decrease degree of gas pressure in relief layer is not obvious within 200h after the first coal seam is mined.With the passage of time,the gas pressure begins to decrease gradually,and the decrease amplitude of gas pressure in the middle area of relief layer is the largest.Uniform distribution load,coal seam gas pressure and initial permeability of coal seam are all positively correlated to the decrease rate of gas pressure in pressure-relieved coal seam,among which,the original gas pressure of coal seam has the least significant influence,and the initial permeability has the largest significant influence.The research results in this paper can provide a reference for the analysis of stress-fissure gas migration characteristics induced by the first mining layer in Pingmei No.8 Mine and other mines with similar conditions,and guide the optimization of gas drainage drilling design,so as to achieve the purpose of gas dynamic disaster prevention and control and safe and efficient coal mining.Figure[58]Table[6]Reference[101]... |
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