Study On The Influence Of Different Key Strata Positions Under Thick Loose Strata On Migration Law Of Mining Overlying Strata

In the process of continuous excavation of underground coal and rock mass,the overlying strata movement law in the mining field undergoes a"time-space"dynamic evolution process.With the continuous development of fissures and redistribution of stress,the overlying strata movement evolution law is different under different geological conditions,among which the study on strata movement law is less under the geological condition of thick loose layer.In this paper,Yunjialing Coal Mine is taken as the engineering background,based on the theory of key stratum,combined with the research and conclusions of many scholars at home and abroad in different ways and methods,firstly,the surface subsidence amount and surface subsidence speed are described,and the surface subsidence law under thick loose stratum is obtained.Then,the movement of bedrock under thick loose stratum is studied downward.Through the establishment of two groups of physical simulation comparative experiments of similar materials with different main and sub-key stratum positions,the movement of overlying strata under thick loose stratum is studied comparatively by using various monitoring methods.For the stress distribution of mining overburden,the finite difference numerical simulation software FLAC~3DD is used to analyze the macro mine pressure of 12305 working face under thick loose layer.The main conclusions are as follows:(1)Although the surface subsidence trend under thick unconsolidated layer is similar to mine subsidence trend under other conditions,the subsidence amount is larger and the range is wider.The left and right full mining angles are 70 and 61,the movement angle and boundary angle are 67 and 57 respectively,and the subsidence coefficient is 0.78.(2)Through the comparative analysis of physical simulation experiments of similar materials in different key layer positions,the cross-validation of four scientific testing techniques with high precision,high efficiency and high definition,including fiber grating sensor monitoring,dial indicator measurement,digital close-range photogrammetry and 2D-DIC global deformation field monitoring,shows that when controlling the weighting of working face,the main key layer is the rock layer that causes weighting characteristics of working face,and the breaking of key layer also causes the breaking and sinking of overlying rock.Although there is a slight deviation in monitoring with these four methods,the detection results for the movement law of mining overlying strata are basically the same.The finite difference numerical simulation software FLAC~3DD is used to analyze the maximum vertical stress of 12305 working face under thick loose layer is 35.9Mpa,the maximum floor heave of goaf floor is 1.99 m,and the goaf floor is obviously damaged by shear force within 30 m.