Evolution Of Crack Field In No.3 Coal Roof Of Chengzhuang Coal Mine And Its Effect On High-efficiency Drainage Of Gas

The overburden rock fissures evolution and pressure relief gas migration law is the core technology of “coal and gas safety mining”.The main channel for pressure relief gas migration in fractured zones is also an important part of the overburden fracture field.The distribution of fracture area,morphology,and permeability in the fractured zone determines whether the long hole surface position of the roof is reasonable,and thus determines the effect of pressure relief gas drainage.This paper uses the theories of masonry beam theory,seepage mechanics,and fluid mechanics,and uses the methods of theoretical analysis,similarity simulation,numerical simulation,and on-site verification to study the rigid laps of internal rock blocks in the “O” ring.The calculation of the gas flow model under the U-type ventilating conditions is based on the calculation of the area of the fractured crack and the area of the broken fracture formed in the internal fracture block of the “O”-shaped ring.The observation of the crack field in the Chengzhuang Mine has verified the length of the model to the roof.The guiding significance of the reasonable layout of drilling holes has achieved the following results:(1)Based on the assumption of rigid block,the area of fracture fissure and separation fractures were calculated theoretically.It is considered that the area of the separation fractures were not very large in the inclined section,while the fracture fissure decreases rapidly on the inclined section.(2)The fracture fissure and separation fractures of overburden rock occurrence and development were analyzed,the evolution of two kinds of fracture experienced change,overburden by elastic zone to the plastic zone of crack to the high layer and development trend and showed "O" type ring distribution in three stages,in the final form of the fracture field in the crack opening angle,frequency,different distribution.(3)By observing the fractured field of overlying strata in the 4308 incoal face of Chengzhuang Mine,the effective range of the gas flow field is that the area above the top of the coal seam is greater than 20 and less than the area inside the incoal face,and the gas flow and concentration of the 2# borehole can be maintained.The high level shows that the best extraction location in the above-mentioned effective range is located in the left area of the lower part of the fissure field on the side of the return wind tunnel.(4)Based on the multi physics field coupling software COMSOL MULTIPHYSICS,the gas migration and concentration distribution in goaf under U ventilation were simulated.Under the U ventilation condition,the fluid velocity near the "O" type circle is about 3~5 times the velocity in the middle part of goaf.