Constitutive Model And Numerical Analysis Of Structured Soil

In this paper, cement and ice are mixed with silty clay in freezing room to make artificial structured soil samples for a series of tests, including isotropic compression, constant-sphere-stress triaxial compression, drained and undrained triaxial compression at several strain rates, and cyclic triaxial compression under constant confining pressure and constant sphere stress. The influence of structure, viscosity, consolidation pressure, drainage condition and stress path, on the mechanic and deformation characteristic of structured soil is studied. The same study is conducted parallely on remoulded soil for comparision. Based on experimental investigation, two anisotropic elastic visco-plastic damaging (EVPD) models-reference time surface model and reference time line model, are proposed for simulation of time-dependent deformation of structured soil under monotonic loading. Two anisotropic elasto-plastic and damaging(EPD) models梑ounding surface masonry model and hypoplasticity disturbed state concept(DSC)model, are presented for simulation of deformation of structured soil under complex loading. These four models' parameters can be determined conveniently by tests with simple stress path. The reference time surface EVPD model is developed traditionally, seperating viscous deformation from instant plastic deformation (including damaging deformation); while in the reference time line EVPD model, it is considered that viscous deformation occurs at any stage of loading, so the viscous deformation and instant plastic deformation (including damaging deformation) are not seperated but modelled as a whole. In the bounding surface masonry model, the sliding yield surface is considered as isotropic hardening and rotating hardening bounding surface, and the masonry model is expanded from monotonic loading to complex loading. In the hypoplasticity DSC model, the scalar normalized stress ratio r| is defined relevant to stress turning angle, and based on disturbed state concept and hypoplasticity theory, the anisotropic plastic modulus is derived to describe the deformationcharacteristic of structured soil under complex loading, including unloading extraction. The validity of the four models has been verified through the comparison between predicted results and the experimental data under monotonic and complex loading. In addition, the capability of the hypoplasticity DSC model is emphaticly studied to simulate complex loading such as stress path turning, rotating shear, rotation of the axis of principal stress, etc.In order to make the proposed models applicable to practice, the matrix of the reference time line EVPD model and hypoplasticity DSC model are derived for FEM numerical analysis. The decoupling solution methods for static and dynamic Biot consolidation equation are proposed. For the static problem, EVPD FEM analysis is performed for a test embankment in an international competition in Finland. The computed results are compared with measured data, and the coupling effect of structure, viscosity and consolidation is discussed. For dynamic problem, the unsimultaneous staggered iteration FEM method with explicit central difference scheme is used for the elasto-plastic analysis of the dynamic response of a soil foundation. The computed results show good agreement with soil mechanic knowledge.At last, fluid dynamic mechanics theory and wave propagation dynamic FEM method are used to analysize a blast centrifuge model test, and the computed results agree well with the measured data. Some useful conclusions are drawn from the analysis.