Classification And Instability Mechanism Of Anchored "Beam-arch" Composite Structure In Rock Burst Roadways With Top-coal

The rock burst of roadways with top-coal in China is frequent,and the roof disaster is particularly serious due to many factors,among which the characteristics of the roof anchoring structure play an important role in the rock burst of roadways with top-coal.This thesis presents a comprehensive study of the anchoring “beam-arch”structure of roadways with top-coal,based on engineering research,theoretical analysis,physical experiments,numerical simulation and machine learning.It investigates the classification model of the structure,the mechanism of rock burst instability,the risk assessment of rock burst and the prevention and control practice.A statistical analysis of rock burst cases reveals a positive correlation between the frequency and severity of rock burst damage and the thickness of top-coal in roadways.The occurrence of roadway rock burst is influenced by geological structure,abutment pressure,cyclic dynamic and other factors.The rock burst characteristics of the roadway are less related to the energy released by the surrounding rock when the support strength is higher.This thesis reveals the different types of anchored “beam-arch” structures of the roof of the roadways with top-coal,depending on the thickness of the top coal.These include the “superimposed-beam and arch” structure for the roadways with thin topcoal,the “composite-beam and arch” and “combined arch” structure for roadways with thick top-coal,and the “combined arch” structure for the roadways with extra thick top-coal.The thesis also clarifies the transformation process from “beam” to “arch”under the dual characteristics of “beam-arch” of thick coal beam.The thesis examines the factors affecting the bearing strength of the “beam” in roadways with top-coal,such as the vertical load and the width of the roadway.It also determines the optimal thickness of the outer “bearing arch”(3～5m)and the inner arch(40～50% of the anchor cable length).It further clarifies that the roof failure and the wall failure of the roadways with top-coal are different types of instability: structural instability and rock burst nuclear failure,respectively.This thesis explores the amplification effect of the anchored “beam-arch”structure on the external dynamic and static stress,and proposes a mechanism for the rock burst instability of the roadways with top-coal.The mechanism involves the failure of the internal structural stress of the “beam” or the “arch” when it exceeds its tensile or shear limit strength under dynamic and static stress,respectively.The thesis argues that the stress amplification effect of the structure is the key factor for the rock burst instability of the roof of the roadways with top-coal.The thesis also reveals a positive correlation between the diffraction dynamic stress of P and S waves and the frequency and peak particle velocity of elastic waves,and constructs an evaluation method for the instability of the anchored “beam-arch” structure under dynamic stress.This thesis reveals the intensification effect of the cyclic dynamic on the rock burst failure of the roadways with top-coal.It proposes a positive correlation between the stress increment of the surrounding rock and the energy level and frequency of the cyclic dynamic.It also establishes a cumulative expression for the stress increment of the surrounding rock under the cyclic dynamic.Moreover,it summarizes the characteristics of the anti-rockburst strength loss of the anchored “beam-arch”structure under the cyclic dynamic load.This thesis summarizes the disturbance characteristics and effects of stress environment,dynamic characteristics and surrounding rock structure on the anchored“beam-arch” structure.It reveals the essence of the stress disturbance of the surrounding rock is the increase of lateral pressure coefficient under the main stress deflection.It also clarifies the positive correlation between the fracture length of the surrounding rock of the roadway and the dynamic stress strength and frequency.The results indicate that the peak values of the roof and wall fracture length of the roadway occur at 40° and 10° of the coal seam inclination angle,respectively,and that the fracture morphology of the inner layer of the roof changes from “beam” to “arch”shape when the top-coal thickness exceeds 6m.This thesis establishes a neural network evaluation method of rock burst hazard of the roadways with top-coal.It proposes a purpose of rock burst prevention and control for stress environment,dynamic characteristics and roof structure.It constructs a prevention and control process of self-influencing factor analysis,rock burst risk assessment and pressure relief measures.It applies the research results in PJH 103 working face and Shanzhai 25031 working face,and demonstrates remarkable prevention and control effects and good socio-economic effects.This thesis has 189 figures,29 tables and 237 references.