Macro-Mesoscopic Failure Process And Numerical Simulation Of Fractured Rock Mass

With the construction of major infrastructure projects for transportation,water conservancy and hydropower,China has become the country with the largest scale and difficulty in the construction of tunnels around the world.These tunnels and other rock projects will encounter various complicated geological conditions and external environmental conditions during the construction process.The large deformation of fragmented surrounding rock and the large volume of landslides induced by it are a common form of disaster in tunnel engineering.Therefore,the analysis and study of the deformation and failure process of fractured rock mass have a very important practical and social significance for the long-term stability of tunnel operation.After a long period of formation,the rock has a large number of random natural defects in its formation process.Its deformation and failure law is affected by the surrounding mechanical environment and its own strength conditions.In addition to the above factors,the influence of its own crack should also be considered in the deformation and failure mechanism of cracked rock.Moreover,the entiredeformation-collapse process of the tunnel fractured surrounding rock is essentially a continuous to non-continuous process.Therefore,it is not scientific to analyze the whole process simply by continuous method.For the area where the collapse has occurred,it should be regarded as non-Continuous area.So we combine the continuous and discontinuous analysis methods to study the deformation and collapse-failure process of fractured rock mass.In this paper,the indoor photoelasticity test is used to analyze the deformation evolution law of fractured rock mass from macroscopic and meso-scopic perspectives based on the energy dissipation theory,and a regional coupling numerical analysis method based on bridge domain method is proposed.The main research content of this paper is as follows:(1)Using a reflective photoelastic instrument,a uniaxial compression test for multi-scale rock deformation and failure with different angle cracks was carried out.The stress and strain of the whole surface of the specimen was calculated based on the optical-stress law.Combining with the results of stress and strain measured by the microcomputer-controlled electro-hydraulic servo universal testing machine,the common impact of the specimen size and crack angle of the fissured rock were analyzed for the strength and failure mode of the fractured rock.And the evolution of cracked rock was studied.(2)Based on the principle of energy dissipation and the theory of strain energy density,combined with laboratory tests,a continuous method was used to study the energy change of fractured rock mass in a nonlinear damage process from a macro perspective.The damage variable is introduced,and the damage constitutive model of fracture rock considering the size effect is established.The relationship between the damage constitutive model parameters and the specimen size and joint inclination angle is discussed.The energy criterion for nonlinear damage damage of fractured rock is proposed.Based on the above constitutive equations and discriminant criteria,the calculation program of fracture of the fractured rock mass is developed,which is based on the FLAC3D software platform.The nonlinear damage process of fractured rock mass is simulated and analyzed.The simulation results are basically the same as the test results.(3)Based on Helmholtz free energy,the contact damage variable is introduced.From the mesoscopic level,the relationship between particle forces and displacements in particle discrete element is analyzed,and a particle damage contact model is built.Based on the open source discrete element software YADE,the above-mentioned damage contact model is used to numerically simulate the deformation and failure process of fractured rock under uniaxial compression conditions.It is verified by laboratory tests.At the same time,numerical experiments on the meso-deformation failure of fractured rock under triaxial compression are carried out.And the influence of crack angle and specimen size on the deformation failure process under triaxial compression is analyzed.(4)Based on the bridge-domain method,the energy weight function is introduced,and the compensation forces(torques)of different models are derived.A macro-mechanical failure coupling analysis model of fractured rock was established,and the program code of the coupling region was developed.The progressive failure process of fractured rock was calculated and compared with that of the pure discrete element model,verifying the correctness and effectiveness of the above coupling method.(5)Based on the above research,using the Chaohui highway tunnel and Changgang tunnel project as background,the pure discrete element model of particle damage contact and the regional coupling model proposed in this paper are adopted to analyze the process of large deformation-collapse of tunnel surrounding rock under different load conditions.