Effect of microstructure on undrained behaviour of sands

Abstract

This paper presents a mathematical modelling of the effects of initial fabric on the mechanical behaviour of sand. A stress-dilatancy model that incorporates microstructural aspects of sand is hereby obtained while writing energy conservation for an ensemble of particles over a representative elementary volume at micro-and macro-scales. The resulting stress-dilatancy model, when used within an elastoplastic framework, successfully reproduces certain aspects of sand behaviour that are reflective of its microstructure under both drained and undrained conditions. The role of microstructure in relation to the characterization of steady, quasi-steady, and phase-transformation states is discussed within the framework of the model. Numerical simulations obtained from the proposed model are generally very consistent with experimental observations and provide insightful information.Résumé : Cet article présente une modélisation mathématique des effets de la fabrique initiale sur le comportement mécanique du sable. Un modèle de dilatance sous contrainte qui incorpore les aspects microstructuraux du sable est obtenu ici en écrivant la conservation d'énergie pour un ensemble de particules dans un volume élémentaire représentatif aux échelles micro et macro. Le modèle résultant de dilatance sous contrainte, lorsque utilisé dans un cadre élastoplastique, reproduit avec succès certains aspects du comportement du sable qui réfléchissent la microstructure dans des conditions tant drainées que non drainées. Le rôle de la microstructure en rapport avec la caractérisation des états permanent, quasi permanent et de transformation de phase est discuté dans le cadre du modèle. On trouve que les simulations numériques obtenues avec le modèle proposé sont généralement très consistantes avec les observations expérimentales en plus de donner des informations très pertinentes.

Effect of fabric on the strength of granular materials in biaxial compression

“…Wan and Guo [6] accounted the effect of inherent anisotropy in micro-level analysis by the ratio of projection of major to minor principal values of the fabric tensor along the direction of the principal stresses. Li & Dafalias [7,8] incorporate this effect by the fabric tensor which was proposed by Oda and Nakayama [16].…”

“…To include the fabric evolution (or induced anisotropy) a function in which changes of the contact normals is included must be defined. Wan and Guo [6] used the following equation:…”

“…The equation can predict the difference between samples due to the fabric which is a combination of the inherent and induced anisotropy as follows: (6) ,where m is a constant that depends on the interparticle friction angle, ȝ and the shape of the particles. When the samples are subjected to the shear loads have a same density their difference in the shear strength due to the fabric can be attributed to the equation (6).…”

“…In other words, the combination of anisotropic parameters (for inherent and induced anisotropy) as the proposed form in Eq. (6), is proportion with the shear strength. The variation of right side of Eq.…”

“…By using this method a constitutive model was proposed to account fabric anisotropy. Direct incorporation the effect of fabric in the constitutive equations starts with the work of Wan and Guo [6]. They used the ratio of the components of the fabric tensor as an affective parameter to show the effect of fabric and its evolution during shearing mechanism.…”