The rigid body limit equilibrium method(RBLEM) and finite element method(FEM) are two widely used approaches for rock slope's stability analysis currently. RBLEM introduced plethoric assumptions; while traditional...The rigid body limit equilibrium method(RBLEM) and finite element method(FEM) are two widely used approaches for rock slope's stability analysis currently. RBLEM introduced plethoric assumptions; while traditional FEM relied on artificial factors when determining factor of safety(FOS) and sliding surfaces. Based on the definition of structure instability that an elasto-plastic structure is not stable if it is unable to satisfy simultaneously equilibrium condition, kinematical admissibility and constitutive equations under given external loads, deformation reinforcement theory(DRT) is developed. With this theory, plastic complementary energy(PCE) can be used to evaluate the overall stability of rock slope, and the unbalanced force beyond the yield surface could be the identification of local failure. Compared with traditional slope stability analysis approaches, the PCE norm curve to strength reduced factor is introduced and the unbalanced force is applied to the determination of key sliding surfaces and required reinforcement. Typical and important issues in rock slope stability are tested in TFINE(a three-dimensional nonlinear finite element program), which is further applied to several representatives of high rock slope's stability evaluation and reinforcement engineering practice in southwest of China.展开更多
Soils with strain-softening behavior — manifesting as a reduction of strength with increasing plastic strain — are commonly found in the natural environment. For slopes in these soils,a progressive failure mechanism...Soils with strain-softening behavior — manifesting as a reduction of strength with increasing plastic strain — are commonly found in the natural environment. For slopes in these soils,a progressive failure mechanism can occur due to a reduction of strength with increasing strain. Finite element method based numerical approaches have been widely performed for simulating such failure mechanism,owning to their ability for tracing the formation and development of the localized shear strain. However,the reliability of the currently used approaches are often affected by poor convergence or significant mesh-dependency,and their applicability is limited by the use of complicated soil models. This paper aims to overcome these limitations by developing a finite element approach using a local arc-length controlled iterative algorithm as the solution strategy. In the proposed finite element approach,the soils are simulated with an elastoplastic constitutive model in conjunction with the Mohr-Coulomb yield function. The strain-softening behavior is represented by a piece-wise linearrelationship between the Mohr-Coulomb strength parameters and the deviatoric plastic strain. To assess the reliability of the proposed finite element approach,comparisons of the numerical solutions obtained by different finite element methods and meshes with various qualities are presented. Moreover,a landslide triggered by excavation in a real expressway construction project is analyzed by the presented finite element approach to demonstrate its applicability for practical engineering problems.展开更多
The stability behaviour of unsaturated soil slopes under rainfall conditions is investigated via a parametric finite element analysis, which is a fully coupled flow and deformation approach linked to a dynamic program...The stability behaviour of unsaturated soil slopes under rainfall conditions is investigated via a parametric finite element analysis, which is a fully coupled flow and deformation approach linked to a dynamic programming technique for determining the minimum factor of safety as well as its corresponding critical slip surface based on the stress fields from the numerical computation. The effects of rainfall features, soil strength parameters and permeability properties on slope stability are studied. The analyses revealed that the soil matric suction decreased during rainfall, especially in slopes with high permeability and/or with high suction angles of unsaturated soils. The influence of rainfall conditions on such slopes is quite obvious, and soil suction drops rapidly, which leads to a consequent quick reduction in the factor of safety.展开更多
Numerical analyses of earthquake effects on the deformation, stability, and load transfer of a slope covered by deposits are traditionally based on the assumption that the slope is a continuum. It would be problem...Numerical analyses of earthquake effects on the deformation, stability, and load transfer of a slope covered by deposits are traditionally based on the assumption that the slope is a continuum. It would be problematic, however, to extend these approaches to the simulation of the slide, collapse and disintegration of the deposits under seismic loading. Contrary to this, a discrete element method （DEM） provides a means to consider large displacement and rotation of the non-continuum. To take the advantages of both methods of continuum and non- continuum analyses, seismic responses of a slope covered by deposits are studied by coupling a twodimensional （a-D） finite difference method and a 2-D DEM, with the bedrock being modelled by the finite difference grids and the deposits being represented by disks. A smooth transition across the boundaries of the continuous/discontinuous domains is obtained by imposing the compatibility condition and equilibrium condition along their interfaces. In the course of computation, the same time-step value is chosen for both continuous and discontinuous domains. The free-field boundaries are adopted for lateral grids of bedrock domain to eliminate the radiation damping effect. When the static equilibrium under gravity load is obtained, dynamic calculation begins under excitation of the seismic wave input from the continuum model bottom. In this way, responses to the earthquake of a slope covered by deposits are analyzed dynamically. Combined with field monitoring data, deformation and stability of the slope are discussed. The effects of the relevant parameters of spectrum characteristic, duration, andpeak acceleration of seismic waves are further investigated and explained from the simulations.展开更多
Traditional rigid body limit equilibrium method （RBLEM） was adopted for the stability evaluation and analysis of rock slope under earthquake scenario. It is not able to provide the real stress distribution of the st...Traditional rigid body limit equilibrium method （RBLEM） was adopted for the stability evaluation and analysis of rock slope under earthquake scenario. It is not able to provide the real stress distribution of the structure, while the strength reduction method relies on the arbitrary decision on the failure criteria. The dynamic limit equilibrium solution was proposed for the stability analysis of sliding block based on 3-D multi-grid method, by incorporating implicit stepping integration FEM. There are two independent meshes created in the analysis： One original 3-D FEM mesh is for the simulation of target structure and provides the stress time-history, while the other surface grid is for the simulation of sliding surface and could be selected and designed freely. As long as the stress time-history of the geotechnical structure under earthquake scenario is obtained based on 3-D nonlinear dynamic FEM analysis, the time-history of the force on sliding surface could be derived by projecting the stress time-history from 3-D FEM mesh to surface grid. After that, the safety factor time-history of the sliding block will be determined through applying limit equilibrium method. With those information in place, the structure＇s aseismatic stability ean be further studied. The above theory and method were also applied to the aseismatic stability analysis of Dagangshan arch dam＇s right bank high slope and compared with the the result generated by Quasi-static method. The comparative analysis reveals that the method not only raises the FEM＇s capability in accurate simulation of complicated geologic structure, but also increases the flexibility and comprehensiveness of limit equilibrium method. This method is reliable and recommended for further application in other real geotechnical engineering.展开更多
The method of nonlinear finite element reliability analysis (FERA) of slope stability using the technique of slip surface stress analysis (SSA) is studied. The limit state function that can consider the direction of s...The method of nonlinear finite element reliability analysis (FERA) of slope stability using the technique of slip surface stress analysis (SSA) is studied. The limit state function that can consider the direction of slip surface is given, and the formula-tions of FERA based on incremental tangent stiffness method and modified Aitken accelerating algorithm are developed. The limited step length iteration method (LSLIM) is adopted to calculate the reliability index. The nonlinear FERA code using the SSA technique is developed and the main flow chart is illustrated. Numerical examples are used to demonstrate the efficiency and robustness of this method. It is found that the accelerating convergence algorithm proposed in this study proves to be very efficient for it can reduce the iteration number greatly, and LSLIM is also efficient for it can assure the convergence of the iteration of the reliability index.展开更多
基金Project(51479097)supported by the National Natural Science Foundation of ChinaProject(2013-KY-2)supported by State Key Laboratory of Hydroscience and Hydraulic Engineering,China
文摘The rigid body limit equilibrium method(RBLEM) and finite element method(FEM) are two widely used approaches for rock slope's stability analysis currently. RBLEM introduced plethoric assumptions; while traditional FEM relied on artificial factors when determining factor of safety(FOS) and sliding surfaces. Based on the definition of structure instability that an elasto-plastic structure is not stable if it is unable to satisfy simultaneously equilibrium condition, kinematical admissibility and constitutive equations under given external loads, deformation reinforcement theory(DRT) is developed. With this theory, plastic complementary energy(PCE) can be used to evaluate the overall stability of rock slope, and the unbalanced force beyond the yield surface could be the identification of local failure. Compared with traditional slope stability analysis approaches, the PCE norm curve to strength reduced factor is introduced and the unbalanced force is applied to the determination of key sliding surfaces and required reinforcement. Typical and important issues in rock slope stability are tested in TFINE(a three-dimensional nonlinear finite element program), which is further applied to several representatives of high rock slope's stability evaluation and reinforcement engineering practice in southwest of China.
基金funded by the Chinese National Basic Research Program (2010CB731503)
文摘Soils with strain-softening behavior — manifesting as a reduction of strength with increasing plastic strain — are commonly found in the natural environment. For slopes in these soils,a progressive failure mechanism can occur due to a reduction of strength with increasing strain. Finite element method based numerical approaches have been widely performed for simulating such failure mechanism,owning to their ability for tracing the formation and development of the localized shear strain. However,the reliability of the currently used approaches are often affected by poor convergence or significant mesh-dependency,and their applicability is limited by the use of complicated soil models. This paper aims to overcome these limitations by developing a finite element approach using a local arc-length controlled iterative algorithm as the solution strategy. In the proposed finite element approach,the soils are simulated with an elastoplastic constitutive model in conjunction with the Mohr-Coulomb yield function. The strain-softening behavior is represented by a piece-wise linearrelationship between the Mohr-Coulomb strength parameters and the deviatoric plastic strain. To assess the reliability of the proposed finite element approach,comparisons of the numerical solutions obtained by different finite element methods and meshes with various qualities are presented. Moreover,a landslide triggered by excavation in a real expressway construction project is analyzed by the presented finite element approach to demonstrate its applicability for practical engineering problems.
文摘The stability behaviour of unsaturated soil slopes under rainfall conditions is investigated via a parametric finite element analysis, which is a fully coupled flow and deformation approach linked to a dynamic programming technique for determining the minimum factor of safety as well as its corresponding critical slip surface based on the stress fields from the numerical computation. The effects of rainfall features, soil strength parameters and permeability properties on slope stability are studied. The analyses revealed that the soil matric suction decreased during rainfall, especially in slopes with high permeability and/or with high suction angles of unsaturated soils. The influence of rainfall conditions on such slopes is quite obvious, and soil suction drops rapidly, which leads to a consequent quick reduction in the factor of safety.
基金the National Basic Research Program of China (Grant No. 2008CB425802)
文摘Numerical analyses of earthquake effects on the deformation, stability, and load transfer of a slope covered by deposits are traditionally based on the assumption that the slope is a continuum. It would be problematic, however, to extend these approaches to the simulation of the slide, collapse and disintegration of the deposits under seismic loading. Contrary to this, a discrete element method （DEM） provides a means to consider large displacement and rotation of the non-continuum. To take the advantages of both methods of continuum and non- continuum analyses, seismic responses of a slope covered by deposits are studied by coupling a twodimensional （a-D） finite difference method and a 2-D DEM, with the bedrock being modelled by the finite difference grids and the deposits being represented by disks. A smooth transition across the boundaries of the continuous/discontinuous domains is obtained by imposing the compatibility condition and equilibrium condition along their interfaces. In the course of computation, the same time-step value is chosen for both continuous and discontinuous domains. The free-field boundaries are adopted for lateral grids of bedrock domain to eliminate the radiation damping effect. When the static equilibrium under gravity load is obtained, dynamic calculation begins under excitation of the seismic wave input from the continuum model bottom. In this way, responses to the earthquake of a slope covered by deposits are analyzed dynamically. Combined with field monitoring data, deformation and stability of the slope are discussed. The effects of the relevant parameters of spectrum characteristic, duration, andpeak acceleration of seismic waves are further investigated and explained from the simulations.
基金Project(2013-KY-2) supported by the State Key Laboratory of Hydroscience and Engineering of Hydroscience, ChinaProject(50925931)supported by the National Funds for Distinguished Young Scientists, China
文摘Traditional rigid body limit equilibrium method （RBLEM） was adopted for the stability evaluation and analysis of rock slope under earthquake scenario. It is not able to provide the real stress distribution of the structure, while the strength reduction method relies on the arbitrary decision on the failure criteria. The dynamic limit equilibrium solution was proposed for the stability analysis of sliding block based on 3-D multi-grid method, by incorporating implicit stepping integration FEM. There are two independent meshes created in the analysis： One original 3-D FEM mesh is for the simulation of target structure and provides the stress time-history, while the other surface grid is for the simulation of sliding surface and could be selected and designed freely. As long as the stress time-history of the geotechnical structure under earthquake scenario is obtained based on 3-D nonlinear dynamic FEM analysis, the time-history of the force on sliding surface could be derived by projecting the stress time-history from 3-D FEM mesh to surface grid. After that, the safety factor time-history of the sliding block will be determined through applying limit equilibrium method. With those information in place, the structure＇s aseismatic stability ean be further studied. The above theory and method were also applied to the aseismatic stability analysis of Dagangshan arch dam＇s right bank high slope and compared with the the result generated by Quasi-static method. The comparative analysis reveals that the method not only raises the FEM＇s capability in accurate simulation of complicated geologic structure, but also increases the flexibility and comprehensiveness of limit equilibrium method. This method is reliable and recommended for further application in other real geotechnical engineering.
基金supported by the National Natural Science Foundation of China (No. 50748033)the Specific Foundation for PhD of Hefei University of Technology (No. 2007GDBJ044), China
文摘The method of nonlinear finite element reliability analysis (FERA) of slope stability using the technique of slip surface stress analysis (SSA) is studied. The limit state function that can consider the direction of slip surface is given, and the formula-tions of FERA based on incremental tangent stiffness method and modified Aitken accelerating algorithm are developed. The limited step length iteration method (LSLIM) is adopted to calculate the reliability index. The nonlinear FERA code using the SSA technique is developed and the main flow chart is illustrated. Numerical examples are used to demonstrate the efficiency and robustness of this method. It is found that the accelerating convergence algorithm proposed in this study proves to be very efficient for it can reduce the iteration number greatly, and LSLIM is also efficient for it can assure the convergence of the iteration of the reliability index.
