Stability Analysis Of Tunnel Surrounding Rock Based On Transverse Isotropic Damage Model

In engineering practice,most of the surrounding rocks involved are layered rocks,and their mechanical parameters will gradually deteriorate with excavation unloading.However,in conventional engineering calculations,the surrounding rock is often assumed to be a homogeneous rock mass with constant mechanical parameters,which leads to large errors in the calculation results.In order to comprehensively consider the influence of rock strength anisotropy and damage deterioration of mechanical parameters on the stability of surrounding rock,this thesis obtains the mechanical parameters of layered rock mass under each dip angle through uniaxial compression test,calculates its damage variables respectively,studies the change law of damage variables with dip angle,corrects the transversely isotropic elastic model and yield criterion based on two sets of damage variables to obtain the transversely isotropic damage model,verifies its rationality through numerical tests,and applies it to tunnel engineering examples.The main contents of this thesis are as follows:?1?Discuss the purpose and significance of the topic selection;The research status of strength anisotropy of layered rock mass,damage mechanics of rock mass,numerical tests and numerical analysis of surrounding rock are summarized.The main work content and technical route of this thesis are pointed out.?2?The layered rock mass is made into standard cylindrical specimens according to different bedding plane inclination angles for uniaxial compression tests;The development law of stress-strain curves of each group of specimens was analyzed.The compressive strength and elastic modulus of each group of specimens are calculated separately,and their variation law with the inclination angle of bedding plane is discussed.?3?Through the statistical strength theory of rock damage and Weibull distribution equation,the damage variables of each group of specimens are solved,and the development trend of the damage variables is discussed.Anisotropy of damage variables is analyzed based on different strain levels.The anisotropy of the damage variable is quantitatively described by the anisotropy of the damage variable.The correlation between the damage variable size and the failure mode of the specimen was analyzed.?4?The transversely isotropic elastic matrix is modified by two sets of damage variables parallel to the plane and along the normal direction of the plane;The transverse isotropic damage model in the global coordinate system is obtained by coordinate transformation.The damage matrix is extracted and its mechanical properties are analyzed.The Mohr-Coulomb yield criterion is modified with damage variables,and is used together with the maximum tensile stress criterion as the yield criterion of the transversely isotropic damage model.?5?Secondary development of transversely isotropic damage model with C++;Based on the self-defined constitutive model,FLAC³DD software is used to simulate the uniaxial compression test done in this thesis.By comparing the calculated compressive strength and elastic modulus with the test results,the rationality of the simulated curve at the front part of the peak is verified.The rationality of the simulated curve at the post-peak part is verified by numerical simulation using a set of triaxial compression tests.?6?Establish a solid model of the tunnel project,and carry out numerical simulation on the initial supporting stage of the tunnel project based on the transversely isotropic damage model and Mohr-Coulomb model respectively,and compare the two calculation results from the aspects of stress,displacement,failure area and internal force of the supporting structure,etc.Based on the monitoring results,the vault settlement and sidewall convergence are compared to verify the reliability of the transversely isotropic damage model.?7?Finally,the conclusions and achievements of this thesis are summarized,and the problems that need to be further studied are prospected.In this thesis,considering the anisotropy of mechanical properties and damage deterioration of mechanical parameters of layered rock mass,a transversely isotropic damage model is derived.After secondary development by C++,a self-defined constitutive model is embedded into FLAC^3D,which can provide a reference for the calculation of surrounding rock stability in tunnel engineering.