Study On Characteristics Of Strata Behaviors Of Mining Above Hollow Area In Yongning Coal Mine

In the process of coal mining,due to exploration conditions,mining technology,economic benefits and other reasons,the lower quality coal resources were first mined,and the relatively inferior recoverable coal seams in the upper part were abandoned.With the increasing demand for coal resources and the non-renewable resources,the contradiction between increasing the recovery rate of coal resources and avoiding waste of resources is becoming more and more important.With the existing theoretical foundation and science and technology,the recovery of coal seams that have not been proven or discarded for various reasons has become an effective way to extend the service life of mines,improve resource utilization,ease corporate pressure,and respond to national energy development routes.However,upstream mining faces many problems.Due to the exploitation of the lower coal seam,engineering disturbances have been caused to the upper coal seam and its surrounding rock structure,destroying its original stress state and causing structural damage,which brings a series of safety hazards to the exploitation of the upper coal seam.When the upper coal seam is located above the curved subsidence zone caused by the mining effect of the lower coal seam,the influence on the roadway excavation,working surface layout and mining of the upper coal seam is small;However,when the upper coal seam is located above the fracture zone or the fallen zone affected by the mining of the lower coal seam,the feasibility of mining and the design of the mining plan must be scientifically discussed and practically tested;When the upper coal seam is located on the irregular slump zone formed by the disturbance of the lower coal seam,it is difficult to have mining property due to the irregular flipping of the coal seam.After the upper coal seam is excavated in a large area in the lower coal seam,the interlayer rock layer is disturbed and moved,deformed and broken,and its bearing capacity is reduced.With the recovery of the upper coal seam,under the disturbance of the secondary engineering,the interlayer rock formation and the surrounding rock structure will be destroyed,which may lead to strong mining pressure such as sinking of the floor surface,causing huge casualties and economic losses.This paper takes the 42 mining area of Yongning Coal Industry in Luliang,Shanxi as the specific engineering background,and uses the combination of theoretical analysis,on-site measurement,laboratory test and numerical simulation to study the feasibility of ascending mining;Under the secondary disturbance,the deformation,movement and failure characteristics of the interlayer rock and surrounding rock structure are analyzed.The joint-surrounding rock interaction system under the secondary disturbance of the uplifting is analyzed,and the overall structural instability and catastrophic process is dynamically analyzed to seek to control the secondary disturbance.The feasibility measures of interlayer rock and surrounding rock structure explore the mechanism of open-pit mining pressure in close range and provide reliable theoretical analysis for close-up upwind mining.The main conclusions are as follows:(1)According to the short-distance mining conditions of the coal seam in the 42 mining area of Yongning Coal Mine,drilling peeping,mechanical test,theoretical analysis and numerical simulation are used to obtain: When the thickness of the interlayer rock between the No.4 coal seam and the 42 mining area coal seam is more than or equal to 18 m,the coal mining in the 42 mining area can be hollowed out;when the working face length of the No.4 coal seam is less than or equal to 150 m,the mining impact is 42.The impact of coal seams in the area is small.(2)The analysis of mine pressure monitoring during the 4206 working face propulsion process shows: When the working face is in the non-hollow area,the mining pressure of the traditional mining face is the same.When the working face is completely in the hollow area,the bearing capacity of the overburden is weakened,and the support load is slightly increased.When the working surface is completely in the hollow area,when the working surface passes through the edge of the hollowed out area,the load of the support increases significantly.Abnormal mine pressure phenomena such as coal wall slabs and slight bottom drums.(3)When the working face enters the edge of the hollowed out area,the pressure of the hydraulic support of the working face,the amount of drilling of the hydraulic support in the leading section,the degree of damage of the coal wall and the deformation of the roadway are observed.If the pressure of the hydraulic support increases rapidly,the amount of drilling of the hydraulic prop increases,When the coal wall is severely damaged and the strong pressure of the bottom drum is manifested,measures such as proper adjustment of the working surface,speeding up the advancement of the working surface,timely replacement of the leading single column,and taking the bottoming of the groove should be taken in time.If necessary,reinforcement measures such as grouting should be taken at the boundary of the hollowed out area.