Structure initiale et propriétés de liquéfaction statique d'un sable

Abstract

A partir de deux modes de reconstitution bien différenciés d'éprouvettes triaxiales de sable, le damage humide et la pluviation à sec, on met en évidence, sur un sable de référence, des différences de comportement mécanique associées significatives visà-vis du phénomène de liquéfaction « statique ». Le damage humide favorise l'initiation de l'instabilité de liquéfaction alors que la pluviation favorise un comportement plus stable, moins liquéfiable. L'observation microscopique des matériaux sableux correspondants permet de mettre en évidence deux structures bien différenciées, à savoir, pour le damage humide, une structure irrégulière dans laquelle prédominent des agrégats (grains agrégés) et des macropores, très contractante et instable et, pour la pluviation, une structure plus régulière, sans macropores, plus dilatante et plus stable. Ces observations montrent l'importance qu'il y aurait à caractériser, à l'aide de paramètres appropriés, la structure initiale des matériaux sableux, directement liée à leur mode de formation (naturel ou artificiel).

Internal states of model isotropic granular packings. I. Assembling process, geometry, and contact networks

“…Zhang and Makse could only approach configurations devoid of hyperstaticity on setting the friction coefficient to infinity (see Section IV D 6 below). The degree of force indeterminacy per degree of freedom on the backbone is still equal, from (34), to 0.141 in D samples and 0.145 in C ones, and varies very little with compression rate in the range we explored, which extends to significantly smaller values than the ones used in [83], as stressed above. It is not obvious whether special experimental situations might occur in which real granular assemblies approach vanishing degrees of hyperstaticity.…”

“…In simulations, A configurations approach their final density within a few tens of time τ = m/(aP ), and come to their final equilibrium with a few hundreds of τ . Comparable laboratory experiments in which dense samples are assembled are sample preparation with the pluviation or rain deposition technique, in which grains are deposited at constant flow rate under gravity, with a constant height of free fall [33,34,67,68]. Such an assembling technique produces homogeneous samples.…”

“…Because of the mechanisms associated with divalent beads z * 0 is strictly smaller than 4. Alternatively, one can define a "corrected" backbone coordination number z * * , as written in (34), which is equal to 4 in the absence of force indeterminacy. As to the global mechanical coordination number z 0 corresponding to the absence of force indeterminacy, its value, given by…”

“…Examples of traditional procedures in soil mechanics are rain deposition under gravity, also known as air pluviation (which produces homogeneous states if grain flow rate and height of free fall [33] are maintained constant) and layerwise deposition and dry or moist tamping. Those two methods were observed to produce, in the case of loose sands, different structures for the same packing density [34]. Densely packed particle assemblies can also be obtained in the laboratory by vibration, or application of repeated "taps" [35,36] to a loose deposit.…”

Efecto de la presión de confinamiento y el método de deposición sobre la respuesta de corte no drenada de arena de densidad media

“…Other studies have shown that specimens prepared by dry funnel pluviation tend to be less resistant than those reconstituted by wet deposition (Mulilis et al, 1977;Yamamuro and Wood, 2004). Other researchers have indicated that tests on samples prepared by dry funnel pluviation are more stable and dilatant than those prepared by wet deposition (Benahmed et al, 2004;Canou, 1989). Vaid et al (1999) confirmed this finding and also showed that wet deposition promotes the quicker onset of liquefaction compared to pluviation under water.…”