Equivalent stress approach in creation of elastoplastic constitutive models for unsaturated soils

This paper introduces an equivalent stress for elastoplastic modeling of unsaturated soils. This equivalent stress unifies various models for unsaturated soils with regard to the stress variables used and allows for a simple separation of the saturated and unsaturated phases of behavior. Moreover, the equivalent stress computed for a given model for unsaturated soil can be used in an existing model for saturated soil so it will gain the ability to model the former. The unsaturated plastic volumetric behavior of the new model is inherited mostly from the parent model for unsaturated soil. The behavior upon shearing depends on both models: the shape of the yield locus is inherited from the original model and the increase of the elastic zone (and possible shift of the elastic zone) from unsaturation depends on the model for the unsaturated soil from which the equivalent stress was taken

Enhancing Constitutive Models for Soils: Adding the Capability to Model Nonlinear Small Strain in Shear

The deviatoric stress-deviatoric strain relationship in soils is highly nonlinear, especially in the small strain range. However, the constitutive models which aim to replicate the small strain nonlinearity are often complex and rarely used in geotechnical engineering practice. The goal of this study is to offer a simple way for updating the existing constitutive models, widely used in geotechnical practice, to take into account the small strain shear modulus changes. The study uses an existing small strain relationship to derive a yield surface. When the yield surface is introduced to an existing soil model, it enhances the model with the nonlinear deviatoric stress-deviatoric strain relationship in the small strain range. The paper also gives an example of such a model enhancement by combining the new yield surface with the Modified Cam Clay constitutive model. The validation simulations of the undrained triaxial tests on London Clay and Ham River sand with the upgraded constitutive models replicate the experiments clearly better than the base models, without any changes to existing model parameters and the core source code associated with the base model

A comparative study of stress integration methods for the Barcelona basic model

The paper compares the accuracy and stability of implicit and explicit stress integration schemes applied to the Barcelona Basic Model. In addition, the effect of the integration scheme on the convergence of Newton–Raphson algorithm is studied. By running a Newton–Raphson algorithm for a single stress point, the number of iterations required to reach convergence gives some insight on the convergence of the finite element solution at the global level. The explicit algorithms tested incorporate substepping with error control and are based on Runge–Kutta methods of different orders or on the Richardson extrapolation method. The implicit return-mapping algorithms follow the procedures of Simo and Hughes [1] and Hofmann [2]

A new SPH-based approach to simulation of granular flows using viscous damping and stress regularisation

Original paperThe smoothed particle hydrodynamics (SPH) method was recently extended to simulate granular materials by the authors and demonstrated to be a powerful continuum numerical method to deal with the post-flow behaviour of granular materials. However, most existing SPH simulations of granular flows suffer from significant stress oscillation during the post-failure process, despite the use of an artificial viscosity to damp out stress fluctuation. In this paper, a new SPH approach combining viscous damping with stress/strain regularisation is proposed for simulations of granular flows. It is shown that the proposed SPH algorithm can improve the overall accuracy of the SPH performance by accurately predicting the smooth stress distribution during the post-failure process. It can also effectively remove the stress oscillation issue in the standard SPH model without having to use the standard SPH artificial viscosity that requires unphysical parameters. The predictions by the proposed SPH approach show very good agreement with experimental and numerical results reported in the literature. This suggests that the proposed method could be considered as a promising continuum alternative for simulations of granular flows.Cuong T. Nguyen, Chi T. Nguyen, Ha H. Bui, Giang D. Nguyen, Ryoichi Fukagaw