Numberical Simulation Of Mechanical Properties And Failure Meachanism Of Fissured Surrounding Rock Using Particle Flow Code

With the high speed development of underground engineering construction in our country, the geological conditions in the process of tunnel construction are becoming more and more complex, especially jointed cracks in the surrounding rock which not only destroys the integrity of the rock mass but also are a impact on the stress and deformation fracture mode of surrounding rock directly, therefore, it has important theoretical and practical significance to study the mechanical properties and failure mechanism of fissured surrounding rock. But the limitations of theoretical and experimental studies of indoor areas restricted its research progress, the numerical simulation method can be used to study the mechanical behavior and failure mechanism of the surrounding rock in the excavation process from the microscopic view better. Considering The Daxiangling Niba mountain tunnel as the engineering background, based on the indoor fractured rhyolite uniaxial and arched tunnels under biaxial compression test,this paper use the particle flow program PFC2D based on discrete element method to research the mechanical characteristics and failure mechanism of surrounding rock under uniaxial compression and biaxial compression. The main contents and results of this paper are as follows:(1) This paper describes the basic principle of discrete element particle flow program PFC2D; through debugging the parameters of fine particles concept, discusses the influence of the parallel bond and friction coefficient of the particles on the macroscopic parameters of rock mass:parallel bond stiffness mainly affects the elastic modulus, parallel bond strength mainly affects the peak intensity, radius coefficient has greater affect on elastic modulus and peak strength, friction coefficient in the range of 0 to 2 has greater affect on the elastic modulus and peak strength, with friction coefficient continuing to increase the affect will be less affected; Determine the fractured rhyolite specimen reasonable mesoscopic parameters.(2) Applying PFC2D to simulate rhyolite specimens under uniaxial compression test, verify that using PFC2D to study the mechanical properties and failure mechanism is feasible by comparing the results of laboratory tests and numerical simulations, then analyze the failure mechanism from microscopic view.(3) This paper analyzes the different preset crack parameters (the angle of single fracture, the rock bridge angle of intermittent double fracture) do the influence on the rock specimen strength characteristics and crack propagation mode combining macroscopic and mesoscopic aspect.(4) By biaxial compression numerical simulation test on surrounding rock of Shing Mun tunnel, we verify the method’s feasibility from fracturing mode of surrounding rock and the train analysis of lateral wall combining with the indoor test results of Shing Mun tunnel, then analyze the fracture mechanism of the surrounding rock mass based on the surrounding rock crack expansion mode, the fracture development characteristics and change characteristics of contact force.(5) Preset different inclinations and different sizes of joints in different positions of surrounding rock of Shing Mun tunnel, then study influence principles that the existing joint have on surrounding rock strength,failure mode and the surrounding rock stability.