Some experimentally based fundamental results on the mechanical behaviour of granular materials

Abstract

Porosity (or void ratio) is one of the most important index measures of granular materials. It alone is not, however, enough for a reasonably complete description of the basicproperties of materials of this kind. The fabric ellipsoid appears to be a good second index measure. It is closely related to the probability density function E(α, β) which defines the angular distribution of the contact normals. Based on experimental evidence the following is concluded. The fabric ellipsoid is closely related to the stress ellipsoid and characterizes a second-order tensor with a clear physical meaning; the principal axes of the fabric ellipsoid seem to tend toward those of the stress ellipsoid and thisappears to hold whether the principal stress axes rotate gradually or discontinuously during a course of deformation; and there seems to exist a quantitative relation between thefabric ellipsoid and the overall applied stresses, especially in the post-failure states.It appears that the function E(α, β) continuously changes in a manner so as to increase the ability of the material to withstand the increased applied stresses. The changes of the fabric, characterized by the changes of E(α, β), result in the hardening (or softening) of the granular materials in a given deformation course. La porositk (ou I'indice des vides) est sans nul doute l'une des mesures caracttristiques les plus importantes en ce qui concerne les matériaux granulaires. Cependant, elle ne permet pas, à elle seule, de fournir une description suffisamment compléte des propriétés de base de matériaux de ce type. L'ellipsoïe de la structure semble constituer une seconde mesure caractéristique intéressante. II est éttroitement associé à la fonction densitié probabilité E(α, β) qui définit la distribution angulaire des normales de contact. Sur la base de preuvres expérimentales, on obtient les conclusions suivantes: (a) l'ellipsoïde de la structure est étroitment associé Iéllipsoïde des contraintes et caracttrise un tenseur de second ordre ayant une signification physique Claire; (b) les axes principaux de l'ellipsoïde de la structure semblent tendre vers ceux de I'ellipsoïe des contraintes et il semble que ceci permette de déterminer si les axes principaux de contraintes tournent progressivement ou d'une maniére discontinue au tours d'une période déformation; et (c)il semble qu'il existe une relation quantitative entre I'ellipsoïde de la structure et les contraintes globales appliquées, principalement dans les tats aprés-rupture. I1 semble done que la fonction E(α, β) varie continuellement d'une maniére qui permette au matériau d'accroitre son aptitude à rsister aux contraintes appliquées accrues. C'-à-dire qu'e les variations de la structure, caractérisées par les variations de E(α, β), ont pour résultat le durcissement (ou le amollissement) des matériaux granulaires au tours d'unepéiode de déformation donnée.

Dynamics of dilative slope failure

“…However, the deposit in the experiment experience anisotropic stress conditions; the vertical stress is larger than the horizontal stress due to removal of the horizontal support. The different stress conditions alters the fabric of the deposit (Oda, 1972;Oda et al, 1980) and could change the values for , thus . More research on how to properly model the compressibility is required to resolve this discrepancy.…”

Force transmission in a packing of pentagonal particles

“…The shear strength of dry granular materials is generally attributed to the buildup of an anisotropic structure during shear due to friction between the particles and as a result of steric effects depending on particle shape [37,38,39]. Several methods have been used to quantify the fabric (structural) anisotropy of granular materials [13,40,41].…”

Modeling of Geomaterials Behavior

“…Oda (1977) illustrated the signiˆcance of the coordination number (number of contacts per particle) for soil response using glass ballotini as a model soil. These publications in Soils and Foundations in the 1970s directly in‰uenced the discussion on soil micromechanics given by Oda et al (1980). Oda (1982) used the ideas of Satake (1978) and Kanatani (1981) to calculate a fabric tensor for the contact normal orientations.…”