Elastoplastic Constitutive Models For Unsaturated Soils With Finite Element Modeling And The Applications In Slope Deformation Analysis

Soils consist of solid granules and pores between those granules.Correspond to saturated and unsaturated soils,the pores it can be fully or partly saturated by liquids.Unsaturated soils are widely distributed above the ground water table around world.The saturation of unsaturated soils changes with the influence of hydrological environment,such as rainfall and ground water table fluctuation.The degree of saturation affects the stress-strain behavior with two main aspects,on one hand the effective stress of soils drops with degree of saturation raises,another respect the material features of unsaturated soils,for example the size of the yield surface,will change with saturation degree changes.Slope deformation and stability are fundamental issues in engineering practices.Reports show that the precipitation and underground water table fluctuation plays an important role in slope's deformation evolution.However,soil slope contains large amount of unsaturated soils because of the terrain and the underground water table distributing.It has a great effect to analyses the slope deformation features with pore fluid flow-stress coupling.Reports show that most researches about slope deformation and stability with pore fluid flow-stress coupling based on effective stress principle.A few literatures relied on the material features of unsaturated soils associated with degree of saturations' variation.Therefore,compute deformation and stability of unsaturated soils slope associated with constitutive model of unsaturated soils be of great significant.Additionally few of current methods considered about hydraulic hysteresis with finite element method numerical modeling.As a realization,focusing on the unsaturated soils constitutive model numerical modeling with hydraulic hysteresis has a theoretical significance.Respect to the importance of unsaturated soils stress-strain relations in researching slope deformation evolution,concerning the insufficient of unsaturated soils constitutive model numerical modeling,a finite-element treatment associated with an extended camclay constitutive model for unsaturated soils has been adopted during this research.An explicit stress integration algorithm with a sub-stepping scheme for unsaturated soils extended camclay model been implemented using Abaqus Umat subroutine.Based on the foundation of extended camclay model,an extended bounding surface elasto-plastic constitutive model for unsaturated soils associated with degree of saturation been established in this thesis.An Umat subroutine described the stress-strain behavior of the extended bounding surface model for unsaturated soils with sub-stepping explicit stress integration method had been added into Abaqus.Finally,the extended camclay model and the extended bounding surface model for unsaturated soils have been applied in transient flow analysis for an ideal slope model deformation process modeling under rain fall condition.Compare to the simulation result from the conventional modified camclay model,the extended camclay model and the extended bounding surface model show strong reliability and wide range of adaptability for modeling unsaturated soils properties.The main results are listed as follows(1)Unsaturated soils extended camclay model with explicit stress integrationConnecting the yield surface function,hardening law and flow rule of the extended camclay model for unsaturated soils,assistant with consistence condition,the elasto-plastic stiffness matrix been derived by assuming the saturation increment as a strain component.Use explicit modified Euler method with error control sub-stepping scheme to solve the constitutive ordinary differential equation.Compere with conventional stress integration algorithm,this new algorithm for unsaturated soils is more briefly and clearly.Then the unsaturated soils extended camclay model was added in Abaqus to carry out numerical experiments under various conditions.The correctness of the model program was verified,and the applicability of the model was explored.The extended camclay model shows a good agreement with unsaturated soils stress-strain behavior.Moreover,because of the hydraulic hysteresis effect considering,the extended camclay model shows more suitable for dry-wet cycle process simulating.(2)Unsaturated soils extended bounding surface model with explicit stress integration.According to the unsaturation hardening law of the extended camclay model,an extended bounding surface model been built for unsaturated soils in order to simulate load-reloading effect on the properties of unsaturated soils stress-strain behavior.Combine with the bounding surface equation,non-associated flow rule and hardening law,the elasto-plastic stiffness matrix been derived by assuming the saturation increment as a strain component.Use explicit modified Euler method with error control sub-stepping scheme to solve the constitutive ordinary differential equation.The extended bounding surface model plays a good agreement with phenomenon of both loading-reloading and dry-wet cycle process of unsaturated soils.(3)Shear band soils unsaturated direct shear test and model parameter fittingTake soil specimen from shear band of Huangtupo landslide in the Three Gorges reservoir,do the direct shear test with different value of constant matric suctions.Use extended camclay model and extended bounding surface model to simulate the direct shear test and fit the model parameters.The simulation results shows that,the extended camclay model performance an obvious strain hardening during the whole plastic deformation stage,while the extended bounding surface model represent an obvious strain hardening in the begging followed by a strain softening stage.Compared with the extended Cambridge model,the fitting result of extended boundary surface model is closer to the experimental curve.(4)Study on deformation evolution of ideal slope model under heavy rainfall infiltration.For the ideal slope model,the extended camclay model of unsaturated soils and the extended boundary surface model are used to simulate the deformation evolution characteristics under the condition of strong rainfall infiltration,with the parameters fitted by the direct shear test.The simulation results are compared with those of the traditional modified camclay model using the pore fluid flow-stress coupling analysis.The analysis results reflect a significant influence by the saturation transformation to the deformation performance of ideal slope model under rain fall condition.Because of the saturation changes,slope displacement computed by extended bounding surface model and extended camclay model are larger than the displacement simulated by modified camclay model.Moreover,the strain distribution of extended bounding surface model and extended camclay model are obviously affected by rainfall infiltration and more concentrated on the slope surface than that of the modified camclay model.The deformation performance of ideal slope modeled by three constitutive relations show three stages of slope deformation evolution with time,which are initial deformation stage,stable deformation stage,and accelerated deformation stage until failure.Because of the absence of the pure elastic deformation in extended bounding surface model,turning between stable deformation stage and accelerated deformation stage is vague,but the results from extended camclay and modified camclay are very clear.So the extended bounding surface model is more suitable for simulating the high fluid clay material.