Study On The Disaster-Causing Mechanism And Control Criteria Of The Hard And Thick Roof Strata Based On Medium Thick Plate Theory

There are a large number of coal seams with hard thick roof in China.When long-wall mining is carried out in this kind of coal mine,strong ground pressure behavior is easy to occur,such as the accidents of large-scale roof-cutting weighting,hydraulic support crushing,rib spalling and roof falls,which seriously affect the safety of mining.The first weighting interval of roof in long-wall working face is generally not more than 40 m.It cannot meet the condition of thin plate whose thickness-span ratio ranges from 0.125 to 0.2 even if the main roof is thinner.However,it is not appropriate to analyze the stress and breakage of roof according to the thin plate theory especially in hard thick roof working face.In addition,the weighting internal,the weighting strength and the weighting duration are generally different in the inclined direction of working face,especially in the super-long working face.Therefore,In order to reveal the form of space breaking after the hard roof is broken,based on the theory of medium thick plate,this paper studies the damage mechanism of hard thick roof and puts forward the control methods.There are three fully mechanized longwall working faces with hard and thick roof are taken as the engineering background of this paper,including top-coal caving face with large mining height and large height work face with composite roof.The theoretical analysis,numerical and physical simulation are used in this study.The theoretical analysis of deformation and failure of the hard and thick roof,the spatial form of the broken thick roof and the movement behavior of overlying strata,and the mechanism of roof failure and dynamic load occurrence are studied systematically in this thesis.The innovative achievements have been made in the following aspects:(1)The theoretical model of the medium-thick plate is deduced which is appropriate for the hard and thick roof of a coal mine.The theoretical solution of the deformation and stress distribution of the first mining face and the island face is given.The mechanical model of overburden breakage and movement is established,the formulas of failure location and angle are given,and the spatial form of overburden movement is analyzed.(2)The damage mechanism of the hard and thick roof is revealed.A method to calculate the dynamic load of roof shear failure is proposed.The stiffness coupling effect in support-surrounding rock system is analyzed.The comprehensive supports selection method of "dynamic load method-stiffness coupling" is innovated.A new method of flexible large deformation reinforcement of coal body is proposed,and the parameters of the flexible reinforcement are optimized.(3)A 3D physical simulation platform is developed to simulate the fracture evolution of the hard and thick roof.The stiffness testing system and experimental method are developed to test the stiffness of the support and immediate roof under the condition of thick roof.The dynamic impact coefficient is also corrected.Based on the stress and strain and deflection equations in the theory of medium and thick roof,the failure location,fracture shape of the roof can be determined.The 3D physical simulation platform successfully simulates the failure behavior and spatial structure of hard roof under different conditions of overburden thickness.The movement characteristics of the roof in the inclined working face with large angle are validated by the field measurement and the surface subsidence law obtained by probability integral method.The developed stiffness testing system is used for impact tests under different roof conditions to correct the dynamic load coefficient of thick plate breakage.The determined "dynamic load method-stiffness coupling" comprehensive supports selection method guides the selection of hydraulic support.The flexible large deformation reinforcement technology has realized the effective disaster control of surrounding rock in the stope.The research results of this thesis are verified by the engineering application,which provide a theoretical basis for coal mining under similar conditions,and has both theoretical and practical significance.