Study On The Bearing Characteristics Of Shallow Insufficient Collapsed Gob And Hazard Induced Mechanism In Lower Seam Mining

Setting the dynamic failure,the mechanism of support failure and the control technology in the process of roof collapse under the shallow insufficient collapsed gobs as the background of this thesis,using theoretical calculation,physical simulation,numerical calculation and field measurement etc.multiple methods,revealing the stability characteristics of the roof in the interval gob,exploding the synergistic load-bearing characteristics of the interval pillar and fractured rock mass(FRM),analyzing the propagation of concentrated load in the roof of lower coal,roof behaviors and forming mechanism of impact load,and going to put forward to a method to weaken the dynamic load produced by roof behavior.The research results are going to provide relevant theory support and engineering scheme reference for safely and efficiently mining under similar mining conditions in adjacent mining areas.The mechanical model of the main roof under uniform load and linear load has been established for quantify the internal stress and displacement distribution in the main roof,based on the strength criterion,the characteristics of roof stability of the interval gob under different landforms are determined.The least squares method is using to interpolate the surface contours for establishing the numerical model of coal seam mining under the insufficenr collapsed gob.It is going to reconstructing and inverting the roof behaviors of the interval gob.The 3DEC equivalent representation method was first put forward for the broken rock mass in the mined-out area,and exploited the programs about 3D Voronoi blocks generation,multiple refinement and subdivision.Complement the defect of the built-in modeling algorithm of 3DEC program,calibrated the intact rock mass and joint mechanics parameters,the algorithm of Weibull distribution model is using to realize the random assignment of property parameters of broken rock mass,the compaction characteristics of FRM with different bulking factor is studied.Combined with the bulking factor of main roof and the vertical displacement distribution in the clamped beam,calculated the bearing range and bearing characteristic expression of the gob.Based on the Burgers-Mohr model,a model of the stability and bearing characteristics of the pillar is established,the expression of the overlying load of the pillar under gentle and gully will be obtained respectively.Based on the overburden load,pillar strength and renormalization group theory,the one-dimensional recombinant pillar group model is established,probability density function of instability of pillar is described by Weibull distribution function,the stability of pillars hasbeen evaluated by the theory of fixed point equation.The propagation law of the stress in the floor of the interval gobs was studied by using the theory of the semi-infinite plane and the coordinate translation method,the concentration depth under the pillars is determined by the stress concentration coefficient,therefore,the stress distribution characteristics of the lower coal roof are described clearly.The field measurement and numerical calculation results revealed the change law of the support force in longwall panel under the barrier pillars and mined-out area,described the mechanism of dynamic load formation while repeated mining,and put forward the pre-splitting pillars method with deep holes,optimized holes layout and charge structure,reduced the dynamic load produced by the two layers of gob roof breakage and pillars failure,realized safety mining of lower coal seam.