Inherent anisotropy in a sand

Abstract

Present knowledge of inherent anisotropy is reviewed and the development of a cubical triaxial cell for studying the inherent anisotropy of non-cohesive granular materials is described. This apparatus is unusual as it offers potential independent control of the three principal stresses through flexible stress controlled boundaries, and some discussion of the relative merits of different types of true triaxial cells is offered. Uniform local strain distributions were measured radiographically and favourable comparisons were made with shear box and conventional triaxial results. Samples were prepared in a tilting mould to give different directions of sample deposition with respect to the sample axes and applied principal stress directions. It was found that the inherent geometrical anisotropy produced in samples by pouring through air in one direction corresponded to a strength and prefailure stress-strain anisotropy. For the rounded Leighton Buzzard sand tested in drained triaxial compression, rotating the directions of pouring through 90°, relative to the principal stress axes, resulted in a change in stress ratio at failure of 10% for the same porosity. Differences of well over 200% in the axial strains taken to reach a given prefailure stress ratio were demonstrated. Coincidence between the principal axes of stress and strain increment was shown while these anisotropic effects were occurring. On passe en revue l'état présent des connaissances dans le domaine de l'anisotropie inhérente et on décrit le développement d'une cellule triaxale cubique permettant d'etudier l'anisotropie inhérente de matériaux granularies non-cohésifs. Cet appareil est inhabituel en ce qu'il offre une possibilité de contrôle indépendant des trois contraintes principales au moyen de surfaces flexibles controllées par les contraintes, et on discute des mérites relatifs des divers types de cellules purement triaxiales. On a mesuré les distributions des déformations locales uniformes par une méthode radiographique et on a effectué des comparaisons favorables avec les résultats obtenus dans une boite de cisaillement et dans une cellule triaxiale conventionnelle. On a préparé les échantillons dans un moule que l'on pouvait faire pivoter, de manière à donner diverses directions de dépositton d'échantillon par rapport aux axes de l'échantillon et aux directions des contraintes principales appliqutes. On a trouvé que l'anisotropie géométrique inhérente produite dans les échantillons obtenus en les versant dans l'air sous une certaine direction correspondait à une anisotropie contrainte-déformation pour la résistance et la prérupture. Pour le sable arrondi Leighton Buzzard qui a été utilisé lors des essais de compression triaxiaie avec drainage, une rotation de 90° dans la direction de versement par rapport à l'axe de la contrainte principale a eu pour conséquence un changement de rapport des contraintes à la rupture de 10% pour la même porosité. On a montré qu'il y avait des différences bien supérieures à 200% dans les déformations axiales nécessaires pour obtenir un rapport des contraintes donné. On a montré que les axes principaux des contraintes et des déformations étaient superposés lors de ces effets d'anisotropie.

Experimental investigation on the deformation characteristics of granular materials under drained rotational shear

“…Similar observations have been reported by Arthur and Menzies (1972) in cubical triaxial tests on tilted samples, Oda et al (1978) in plane strain tests, Arthur et al (1981) in directional shear cell tests and Cai et al (2013) in HCA tests.…”

“…Hence, soil anisotropy has attracted long-lasting interest of researchers and practitioners. Arthur and Menzies (1972) reviewed several early studies on the soil anisotropy. They prepared samples in a tilting mould to give different directions of sample deposition with respect to the applied principal stress directions, and found the specimen produced by pouring through air in one direction corresponded to a strength and pre-failure stress-strain anisotropy.…”

“…Oda et al 1978;Tatsuoka et al 1990, Alshibli andSture 2000;Wanatowski and Chu 2006), directional shear cells (Phillips and May 1967;Oda and Konishi 1974a, b;Wong and Arthur 1985), true triaxial apparatuses (Arthur and Menzies 1972;Yamada and Ishihara 1979;Ochiai and Lade 1983;Miura and Toki 1984;Abelev and Lade 2004) and hollow cylinder apparatuses (e.g., Symes et al 1988;Miura and Toki 1986;Vaid et al 1990;Gutierrez et al 1991;Nakata et al 1998;Rolo 2003;Lade et al 2008;Cai et al 2013). …”

Particle mechanics approach to continuum constitutive modelling

“…However, experiments by Al-Tabbaa (1984), Arthur and Menzies (1972), Arthur et al (1977) and others showed that even initially isotropic soils could develop induced anisotropy. This had been defined by Casagrande and Carillo (1944) as anisotropy associated with a history of shearing strain.…”

Fabric, force and strength anisotropies in granular materials: a micromechanical insight

“…Strength anisotropy is of key engineering importance in estimating the stability of infrastructures and has therefore attracted much research interest. Extensive efforts of experimental testing and constitutive modelling have been made to better estimate the strength and deformation of anisotropic granular soils [2,3,5,6,9,19,22,27,29,32,34,42]. Experiments have been carried out by preparing and testing specimens of different tilting angles or loading a soil specimen along various directions [20,29,30,45].…”