Three-dimensional Slope Stability And Failute Analysis Using Shear Strength Reduction Finite Element Method (SSR-FEM)

In engineering practice, the slope stability is usually analzed by the two-dimensional approach. However, most slope failures are three-dimensional in nature, especially for natural slopes or slopes under local surcharge or seisimic loads. In particular, the stabililty analysis of two-dimensional can't reflect the actual state and failure process of slope. So, the three-dimensional stability analysis is popularly expected to evaluate the stability of slopes or stabilized slopes in practice. At present, shear strength reduction finite element method (SSR-FEM), an effective approach, has been widely used in 3D slope stability analysis and accepted by many experts and scholars. But some problems have still not been completely solved. For example, the influence of finite element mesh size on the calculation accuracy; the influence of boundary conditions and strength parameters of rock and soil on 3D slope stability and the potential slip surface; the stability analysis for three-dimensional excavated slopes and the effects under external loads such as the surcharge on the top of slopes and seismic loads; and the application of shear strength reduction finite element method (SSR-FEM) in practical engineering. Based on this, some studies are carried out systematically as below:1) Discussion on the basic issues of 3D slope stability analysisThe SSR-FEM is first adopted to study the effect of element size, instability criteria on the factor of safety and the failure mode. Further, the influence of boundary conditions on the stability and the potential slip surface of 3D slope is discussed. Comparative analysis on the deformation and stability of three-dimensional slope with and without orginal stress in the soils is also made. After that, the relationship between the deformation of 3D slope and strength reduction factor (SRF) is illustrated to visualize the SSR-FEM. The studies can provide a necessary basis for the application of SSR-FEM in 3D slope stability analysis.2) Three-dimensional slope stability and failure analysisThe influence of internal friction angle and cohesion of soils, and slope inclination on slope stability and failure mode such as the depth of potential slip surface, out-slip point and the back crack of slip surface, under different boundary conditions are comprehensively analyzed. Also, the stability and failure mode of 3D slope under uniform locally loaded and pseudo-static seismic loads such as horizontal, vertical and the combination of the two are discussed. In addition, the stability and failure mode of three-dimensional slope with thin weak layer under natural condition and uniform surcharge are compared in details.3) Stability analysis of 3D slopes considering the excavated process and environmental loads by SSR-FEMThe deformation and overall stability of 3D slopes during excavated process is analyzed. The comparative research on the stability and failure mode for 3D slope with and without excavation loads also made. Emphasis is given to discover the influence of uniform loads on the stability and failure mode, even the magnitude and acting position of the loading. By using pseudo-static method, the effect of two horizontal seismic loading on the stability of 3D slope and failure mode is also analyzed. When the slope contains a thin weak layer, the results computed demonstrate that the potential slip surface remarkably depend on the weak layer. The research can provide a reference for similar practical engineering.4) Strengrh reduction FE method's application to Cha'an landslideCombined with the practical engineering, shear strength reduction finite element method(SSR-FEM) is used to analyze the stability and failure mechanism for Cha'an landslide in Dalian of China, some vital factors such as excavated process, groundwater condition, vehicle loads and seismic load are enough considered. Then the limit equilibrium method (LEM) is also adopted to compare with the results from SSR-FEM. Based on this, an old Cha'an landslide is numerically analyzed using the three-dimensional strength reduction elast-plastic FE method. The practice has proved that SSR-FEM is an effective approach to evaluate the three-dimensional slope stability and failure mode.