Fracture Evolution and Its Fractal Characteristics of Overlying Rock in Shallow Burial Extremely Thick Coal Seam Fully Mechanized Mining
The mining of shallow burial extremely thick coal seams can easily induce the formation of air leakage channels through the surface of overlying rock fractures,resulting in difficulties in ventilation management of the working face and spontaneous combustion of downhole residual coal.Taking the 61202 working face of Dafanpu Coal Mine in Inner Mongolia as the research object,UDEC numerical simulation is used to analyze the stress changes and fracture characteristics of the overlying rock strata during the working face mining,and the fracture evolution law and its fractal characteristics of overlying rock are explored.The results indicate that under the condition of shallow burial extrememly thick coal seam fully mechanized mining,the stress of the overlying rock strata will go through three stages:pressure increase,pressure decrease,and re-pressure;The advancing distance of the working face of 0-50 m,60-240 m,and 245-450 m can be divided into three stages of fracture development:"accelerated dimension raising-decelerated dimension raising-stabilize dimension smoothly".The fractal dimension D during the fully mining stage is between 1.011 and 1.341;Based on the characteristics of the three-stage development of fractures,different control methods for fracture development at different stages are proposed to ensure safe production of the working face.The research results are helpful in revealing the development law of fractures in shallow burial extremely thick coal seam fully mechanized mining in the western region.
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