SANISAND: Simple anisotropic sand plasticity model

Abstract

SUMMARYSANISAND is the name used for a family of simple anisotropic sand constitutive models developed over the past few years within the framework of critical state soil mechanics and bounding surface plasticity. The existing SANISAND models use a narrow open cone-type yield surface with apex at the origin obeying rotational hardening, which implies that only changes of the stress ratio can cause plastic deformations, while constant stress-ratio loading induces only elastic response. In order to circumvent this limitation, the present member of the SANISAND family introduces a modified eight-curve equation as the analytical description of a narrow but closed cone-type yield surface that obeys rotational and isotropic hardening. This modification enables the prediction of plastic strains during any type of constant stress-ratio loading, a feature lacking from the previous SANISAND models, without losing their well-established predictive capability for all other loading conditions including the cyclic. In the process the plausible assumption is made that the plastic strain rate decomposes in two parts, one due to the change of stress ratio and a second due to loading under constant stress ratio, with isotropic hardening depending on the volumetric component of the latter part only. The model formulation is presented firstly in the triaxial stress space and subsequently its multiaxial generalization is developed following systematically the steps of the triaxial one. A detailed calibration procedure for the model constants is presented, while successful simulation of both drained and undrained behavior of sands under constant and variable stress-ratio loadings at various densities and confining pressures is obtained by the model.

Validation of a New Elastoplastic Constitutive Model Dedicated to the Cyclic Behaviour of Brittle Rock Materials

“…Contrary to rock materials, different models exist for the cyclic behaviour of sands such as the Prevost model (Prevost, 1985;Cerfontaine et al, 2015), generalised plasticity (Mira et al, 2009) or subloading surface (Hashiguchi, 2009). The formulation proposed hereinafter is based on the bounding surface plasticity (Dafalias, 1986), the pioneering work on its application in form a two surface plasticity model for sands (Manzari & Dafalias, 1997) which was later extended further (Dafalias & Manzari, 2004;Taiebat & Dafalias, 2008;Li & Dafalias, 2012;Dafalias & Taiebat, 2016) and adopted the title of SANISAND, an acronym term for Simple ANIsotropic SAND. This framework is mainly chosen for its ability to reproduce accumulation of plastic strain upon constant amplitude cycles, for its physically based concept and relative simplicity.…”

“…This work is derived from the bounding surface plasticity concept (Dafalias, 1986) and its application in the framework of SANISAND models (Manzari & Dafalias, 1997;Dafalias & Manzari, 2004;Taiebat & Dafalias, 2008;Li & Dafalias, 2012;Dafalias & Taiebat, 2016). This choice is justified by the capability of these models to reproduce accumulation of plastic strain for constant cycle amplitude.…”

“…where n α is a parameter that rules the stiffness and brittleness of the material, and h is defined as (Taiebat & Dafalias, 2008) …”

“…The full development of a multiaxial model is out of the scope of this paper. However generalisation of the model to a multiaxial formulation can be carried out following methodology proposed in (Taiebat & Dafalias, 2008). All the equations are systematically rewritten as function of tensors.…”

Drained and Undrained Shear Behavior of Compacted Coal Wash

“…Taiebat and Dafalias, 2008), a summary of the governing equations capturing anisotropic yielding is given by the following equations (Imam et al, 2005). …”