Research On Dynamic Evolution Law Of Mining Overburden Failure Under Thin Bedrock With Shallow Coal Seam

Water inrush and sand burst under thin bedrock in shallow coal seam is one of the types of roof water damage.Mine water inrush disasters have been plagued by the healthy development of the coal industry,especially in the mining areas of western China,where water inrush and sand bursting are particularly serious.This is because most of the mining areas in the West are shallow coal seams and the overlying bedrock is relatively thin.Once the overlying rock fissures caused by the mining of coal seams run through the aquifer,water inrush and sand bursting are easy to occur.Preventing water inrush hazards in high-intensity mining conditions under the thin bedrock water body of shallow coal seams,ensuring the safe development of coal resources,and avoiding the threat of water inrush and sand collapse during the construction of mines and production processes,which is of great significance to the protection of miners’ lives and national property Meaning.This paper takes the 31114 working face of Jinjie Coal Mine as the geological background,analyzes its hydrogeological conditions,uses empirical formula method,measured analogy method,physical similar model test method and FLAC3 D numerical simulation method to explore the failure laws of mining overburden and draw conclusion.These four methods have obtained similar conclusions,and the ratios of collapse to fracture and fracture to fracture are 3 and 14,respectively,and the overburden failure process is divided into: first collapse section-collapse zone development section-fracture zone development section-cover rock Deformation stabilization section,these four stages.By analyzing the vertical displacement and vertical stress in the physical similarity model test and numerical simulation model,it is obtained that the vertical stress value changes dynamically with the mining of the coal seam: when mining is directly below the measurement point,the overburden layer has a pressure relief effect.When the working face advances farther,the measurement point may enter the coal wall affected area to produce a boosting effect;the measurement points at the same position on the horizontal plane 30,40 m above the coal seam have the same spatial and temporal evolution trend with the advancement of the coal seam,and the 50 m above the coal seam almost Affected by coal seam advancement.Perform a series of processing such as binarization on the fracture pictures of mining overburden,and use PCAS to quantitatively analyze the fractures and obtain the spatial and temporal evolution of the fractures with the working surface: the fracture rate,the number of fractures,and the total length These three indicators,in the process of coal seam mining,have the same general trend of time-space evolution evolution,and all have an upward trend.The average length first decreased slightly after increasing to a certain peak.The average width is decreasing overall.The four stages of productionopening-through-closing occur in the process of coal seam mining crack change process.Combined with the theory of flood risk source,the risk assessment method of fuzzy mathematics is used to assess the flood risk on 31114 face.By analyzing and refining the source of water inrush danger,the target layer,the indicator layer and indicator layer indicators are established respectively Set of comments,and assign points for different evaluation levels;combining the previous real stratigraphic conditions,similar model tests and numerical simulation results to establish a fuzzy secondary index when the working surface is advanced 20,40,60,80,100,120 m,respectively Relation matrix and comprehensive evaluation vector,and then recursive upwards,and finally make a fuzzy mathematical comprehensive evaluation of the overall target(the risk of water inrush from shallow coal seams);put forward effective preventive measures and governance measures for the risk evaluation given by fuzzy mathematics.