| Based on the engineering background of Sangshuping Coal Mine in Hancheng City,this paper starts with the mining of unequal thickness coal seam under the condition of thick hard sandstone roof and the stope space structure formed after the overburden rock is broken.The influence mechanism of ore pressure under the condition of unequal thickness coal seam mining is analyzed.The distribution characteristics of surrounding rock stress,displacement field,elastic deformation energy and plastic zone caused by different mining thickness were studied.In view of the coal seam mining problem under the thick hard roof,the design of roof pre-splitting blasting pressure relief and anti-reflection technology scheme,to ensure the safety and efficient mining face.The main research results and conclusions are as follows:Based on the theory of masonry beam and key layer,the overlying key layer of 4321 working surface is identified,and the mining thickness conditions for the formation of sub-key layer 1 "masonry beam" structure are analyzed and judged.WhenΔj≤Δmax,that is,M≤7.6m,the broken block of sub-key layer 1 has a small rotation space and can form a stable "masonry beam" structure.When M>7.6m,the rotation space of subkey stratum 1 is larger than its limit rotation,and the subkey stratum 1 will exist in the form of "cantilever beam" structure.Combined with the two kinds of structures of the overburden sub-key layer,the calculation methods of the working resistance of the support are presented respectively.According to mulberry ping 4321 face geological conditions,established the hard thick sandstone roof mining thick coal seam physical analog simulation experiment,with the working face advancing,vertical displacement line Ⅰ,Ⅱ,Ⅲ subsidence significantly greater than mined-out area near the face side of the other location;Under the influence of the thick hard sandstone roof,the slope of the subsidence curve near the working face is larger.With the increase of coal seam thickness,the overburden in the middle and upper part of the coal seam is far away from the coal seam,and the subsidence curve is approximately a smooth and continuous "parabolic" symmetrical distribution.However,the subsidence curve of the strata after the periodic fracture of the lower part of the coal seam does not show a symmetrical characteristic due to the increase of coal thickness,and it shows an asymmetric distribution of "wave slope".Using FLAC3D numerical simulation software,the mining model of thick and hard sandstone roof with unequal thickness is established.When the thickness of the coal seam increases from 3m to 10m,the vertical stress peak decreases gradually,and the length of the stress peak from the coal wall increases gradually.The advancing length of working face has a great influence on the maximum subsidence of coal seam roof.When the excavation distance reaches the length of working face,the growth trend of the maximum subsidence of goaf roof slows down gradually.The dynamic change process of overburden failure has obvious characteristics of longitudinal and transverse zoning.The dynamic evolution law of the elastic properties of rock mass under the direction of working face advance and working face layout is obtained.For thick hard thick coal seam of roof and low permeability of complex conditions,from two aspects of coal and rock mass unloading and gas anti-reflection comprehensive governance,pre-splitting blasting design roof pressure,the anti-reflection schemes to determine the reasonable blasting parameters,realized the safety of the hard roof caving,the average cycle to pressure step distance shortened to 12.7 m,stent during the relief valve is not open,after the roof blasting gas return air concentration was reduced by 46.7%,the largest to ensure the safety mining face.Figure 39 table 9 reference 65... |
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