Study On Deformation Mechanism And Failure Characteristics Of Layered Rock Masses Due To Excavation

In the geotechnical engineering, the anisotropy is a very important characteristic of rock masses, while layered rock masses usually display transverse isotropic behiviors which has obviously influence on deformation and stress distribution of rock mass due to excavation. Based on two kinds of typical layered rock masses engineering problems—steep obliquity layered rock masses in large-scale underground powerhouse and antidip layered rock masses in slope engineering, deformation characteristics and failure mechanism under excavation are synthetically analyzed by using theoretical analysis, deformation monitor analysis and numerical simulation in the Longtan Project. Major work and main conclusions are summarized as follows:(1) Based on three kinds of typical joints of layered rock masses, geologic features and structure effect on layered rock masses engineering are analyzed. Then failure types and failure mechanism of layered rock masses are further discussed.(2) Bring forward rapid back analysis method of small sample on initial geostress field parameter based on uniform design and particle-swarm least-squares support vector machine, 3D initial geostress field of underground powerhouse in the Longtan Project is studied, by back analysis, the regularities of in-situ stress field distribution along the depth are obtained.(3) Based on FLAC3 D and its convenient secondary development platform, a transverse isotropic deformation ubiquitous-joint model is put forward by introducing deformation anisotropy into ubiquitous-joint model.Then, the new model is certified using VC++ program language to develop new constitutive model and acquire the model dynamic link file which can be loaded and invoked directly in FLAC3 D.(4) Introducing nonlinear statistical methods, an analytic method for rock and soil mechanics deformation monitoring information based on change point analysis method is brought forward.(5) The influence factor's tendency chart of surrounding rock masses deformation is obtained by making use of orthogonal design and variance analysis to study main influence factors of deformability of layered rock masses in underground structures group.(6) The limit equilibrium method (G-B method) of antidip layered rock masses toppling is improved by considering the influence of underside rock-bridge, non-orthogonal jointed and hydraulic pressure which can explain the upper perched water accelerating slope toppling.(7) Deformation characteristic of surrounding rock masses of underground powerhouses due to excavation in the Longtan Project is studied by using the monitoring displacement analysis method and some other numerical simulations, such as finite element method, discrete element method, and FLAC3 Dmethod. Based on elastic model, Mohr-Coulomb model and transverse isotropic ubiquitous-joint model, stress distribution properties, deformation and failure characteristics of underground powerhouse are synthetically analyzed from multi-scale and multi-method, and some very important conclusions are drawn.(8) Deformation and failure characteristics of antidip layered high rock masses in the left water slope of Longtan project is studied by monitoring displacement analysis method, finite element method, discrete element method and FLAC3 D, And stability of the slope is evaluated.The study of two typical layered rock masses can be a good reference to hydroelectricity and traffic projects.