Study On Gas Migration Of Mined Coal Seam Under The Influence Of Fault

Fault,close distance coal seam,high gas and low permeability are the common characteristics of coal seam assignment in Guizhou,and the coupling of close coal mining and gas transport in the fault structure area seriously affects the safe and efficient production of coal mines in Guizhou.Therefore,this paper takes the actual working conditions of a coal mining face in a mine in Guizhou Province as the research background,and uses theoretical analysis,similar simulation test,numerical simulation and other research means to carry out the research.The results of the research can provide some reference for the mining of close coal seams in the fault structure area,comprehensive gas prevention and control,and ensure the safe and efficient production of coal mines in Guizhou.(1)The theoretical analysis of the mechanical mechanism of the upper and lower working face over the fault was conducted,and it was concluded that the way of advancing the upper working face over the fault is beneficial to the stability of the mining overburden structure compared with the way of mining the lower working face over the fault.The similar simulation test found that the upper working face will form a stable mining overburden structure when excavating to a certain distance from the fault and when excavating to the fault location,which verifies the results of the theoretical analysis.(2)After taking the way of picking the top diagonally upward directly over the fault,the top plate fragmentation at the fault location is very serious,while the sinkage is relatively large near the top of the fault,and the overall sinkage of the upper plate displacement of the positive fault is slightly smaller than the lower plate sinkage.Because of the existence of the fault,compared with the ordinary mining conditions,the largest overburden displacement sinkage will appear near the left side of the middle of the mining area,and the existence of the fault will also make the overburden "trapezoidal" collapse pattern on both sides of the fault is destroyed,the development of discontinuity.(3)By simulating the mining of the close coal seam in the fault structure area through the discrete element method procedure,the mining of the No.5 coal seam is almost unaffected by the fault,and the pressure relief pattern of the overlying rock layer is still presented as a conventional "saddle-like" distribution pattern.The barrier effect of the fault is obvious,which will cause the distribution of two different pressure relief areas of "one high and one low" in the lower rock layer.The bottom drum of the roadway near the top area of the fault is seriously deformed,and there are certain hidden dangers of mining.(4)Under the influence of repetitive disturbance of close seam mining,the mining of No.9 coal seam will cause another small "saddle-like" distribution pattern in the overlying unloading zone.Even if the fault is located in the pressure relief zone,the fault barrier effect is still significant.The stress concentration is more obvious at the local location of the upper working face and near the fault area,and the stress variation value is still larger at the end of the fault(top and bottom)compared with other locations,and the stress concentration is more obvious.(5)The theoretical empirical calculation and the numerical simulation calculate the development height of the riser zone and fracture zone of coal seam No.5 and No.9 are basically consistent;the maximum sinkage of mining overburden displacement of coal seam No.5 and No.9 from similar simulation test and numerical simulation are basically consistent.The spatial and temporal distribution characteristics of mining fissures are quantified by using fractal dimensions,revealing the dynamic evolution process of mining overburden fissures,and exploring the change trend of fractal dimension 1 and 2 of mining overburden fissures under the influence of repeated disturbance in the fault structure area.(6)The gas transport law of the mining fissure field of No.5 and No.9 coal seams in a mine in Guizhou was simulated by multi-physical field coupling simulation software,which initially revealed the gas transport law of close mining coal seams in the area of positive fault structure.Under U-shaped ventilation conditions,the gas accumulation in the upper corner position of the mining fissure field is serious,and the gas generally rises and gathers in the off-set development area of the overlying rock layer.Due to the existence of the fault,even if the mining fissure field of No.9 coal seam mining area is within the close range of No.5 coal seam mining pressure relief,the gas concentration in the mining fissure field is still high and the gradient of gas concentration changes is large,and the gas will circulate actively and accumulate easily near the fault structure.The gas concentration at the upper level of the fault is slightly higher than that at the lower level.