| China’s close-range coal seams are rich in resources and use underground mining methods to exploit underground coal resources.This mining method generally uses the bottom of the upper coal seam as the top plate for the lower coal seams,so that the upper coal seams will be mined after mining.It has a great influence on the surrounding rock stress and surrounding rock state in the lower coal seam.Especially when the interval between the two layers of coal between the layers is small,the strength of the floor of the upper coal layer is damaged to a certain extent,and the self stress of the overlying rock passes through the coal pillars left by the upper coal layer to the floor rock(coal).Layer transfer will produce a local stress increase area in the lower coal seam,and the underlying coal seam will have a more complex stress environment,which will bring great difficulties to the location selection of the roadway and the surrounding rock control during the mining of the lower coal seam.In this paper,the background conditions of the 4th and 4th extremely close coal seam with the interval of only 1m between Shanxi Huaye coal seam as the research background are studied.In order to ensure that the lower 4th coal seam mining roadway is located in the upper 4th coal roadway,the back roadway surrounding rock In terms of stability,the main factors affecting the stability of surrounding rock of roadway in Lower Coal Seam No.4 under the conditions of extremely close-distance coal seam formation are analyzed: the roadway is subject to the stress environment of the coal pillar in the upper part of the No.4 coal seam,the choice of roadway position,and roadway Surrounding rock properties,roadway support methods.Through theoretical analysis,numerical simulation,laboratory tests,site observations and other research methods,the roadway layout and roadway surrounding rock control of the mining roadway in the 1m ultra-close distance coal seam were studied.The main results of the study are as follows:(1)Through the analysis of stress distribution law of surrounding rock in upper coal seam mining,the mechanical model of stress in longwall mining stope is established by using slip field theory and elastoplastic theory,and the failure of bottom plate after mining of No.4 coal seam in Huaye Coal Mine is obtained.The maximum depth is 4.7m,far exceeding the interval between the 4th coal seam and the 4th coal seam.(2)Through the analysis of the stability of coal pillars,a calculation model for the plastic zone of coal pillars was established,and the calculation formula for the plastic zone width of coal pillars was obtained.Combined with the geological data of Huaye Coal Mine,the coal pillars in the stable section of No.4 coal seam were determined.The section between the 4108 working face and the 4109 working face is a stable pillar.(3)Through theoretical calculations and numerical simulations,the vertical stress and shear stress distribution laws of the floor rock surrounding the coal pillars with different widths after coal mining are analyzed,which provides theoretical guidance for the selection of the position of the lower coal seam in the lower 4th coal seam.It is determined that under the condition of 1m layer spacing,the layout of the lower coal seam mining roadway adopts an internal offset arrangement,which is more appropriate and the roadway should be placed in a position where the difference between the vertical stress and the principal stress is relatively small and the stress change is relatively uniform,in combination with the numerical simulation of the vertical stress,the main As a result of the stress difference and the equilibrium degree of its stress variation,the reasonable internal offset distance of the two straight grooves of the lower coal seam 4301 working face is 10 m.(4)Analyzing the failure characteristics and instability law of the roof of the roadway in the goaf,and determine the principle of the control of the roof in the lower coal roadway as follows: 1 fast load 2 vertical preload 3 lateral reinforcement;put forward the use of full-length anchor bolt Joint support of net + I-steel frame and three-dimensional joint control technology based on full-length anchorage of hydraulic expansion anchor and advance-in-place roofing method.Two kinds of support technologies control the roadway surrounding rock;through anchoring bolts for full length Network and I-steel-frame combined support methods are used for numerical simulation,and the feasibility of the support scheme is determined before the underground application.Through on-site industrial testing of the mine roadway pressure observation,the analysis of the roadway leading support monomer column,The deformation of the roadway surrounding rock is affected by the mining activity,and the roof after supporting the roadway is peeked.It is determined that the surrounding rock of the roadway in the lower 4th coal seam of the Huaye Coal Mine is controlled effectively. |
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