The Paper describes an experimental investigation of the stress-strain behaviour of anisotropically consolidated clayey sands, carried out using instrumented and computer-controlled triaxial cells. The specimens were prepared by sedimenting Ham river sand into a kaolin suspension. For a given granular void ratio, as the clay content of the sedi-mented clayey sands increases from 4-6 to 10%, the undrained brittleness and strains to phase transformation also increase, when the specimens are sheared in compression. When sheared in extension, liquefaction takes place for clay contents up to 7-5%. Increases in granular void ratio give rise to increased brittleness and potential to liquefaction. The effects of overconsolidation on strength and stiffness characteristics have been examined. The effective stress paths for undrained shear of the normally consolidated soil form a boundary for the effective stress paths for the lightly overconsolidated soil. L'article décrit une étude expérimentale, effectuée a l'aide de cellules triaxiales instrumentées et con-trôlées par des ordinateurs, du comportement de sables argileux consolidés de façon anisotrope. Les échantillons ont été préparés par sédimentation du sable fluviatile (Ham) dans une suspension de kaolin. Pour un indice des vides entre les grains d'une valeur donnée, à mesure que le contenu d'argile dans les sables argileux sédimentés s'accroît de 4,6 a 10% la fragilité non-drainée et la transformation des déformations en phases s'augmentent aussi lorsque les échantillons sont soumis au cisaillement sous compression. Dans le cas du cisaillement sous extension la liquéfaction a lieu pour des teneurs en argile jusqu'à 7,5%. Des augmentations de l'indice des vides entre les grains provoquent un accroissement de la fragilité et de la liquéfaction potentielle. Les effets de la sur-consolidation sur les caractérisques de résistance et de raideur ont été examines. Les chemins effectifs de contrainte pour le cisaillement non-drainé du sol normalement consolide constituent une limite pour les chemins effectifs de contrainte dans le sol lé-gèrement surconsolidé.
A database of the mechanical behavior of 25 natural sands was compiled from the existing literature. Particle shape and size analysis, obtained by Dynamic Imaging Analysis, for each material in the database has subsequently been linked to its mechanical properties; selected sands were also subject to interferometry study for particle surface roughness measurements. This paper reviews the effect of the particle shape properties of these sands on their Critical State and stiffness parameters, introducing a new parameter to optimize the correlations.
The results of oedometer and triaxial tests on high-quality intact samples of four natural stiff clays are presented and compared with the corresponding results for reconstituted clays. By this means it has been possible to identify the influence of the micro-structure on the compressibility and peak strength of the natural clays. All four clays exhibit rapid loss of strength after peak with well-defined post-rupture strength envelopes. At low confining pressures the post-rupture angles of shearing resistance are all close to the corresponding intrinsic critical state values, but for some of the clays there is a small cohesive intercept. At higher confining pressures the post-rupture angles of shearing resistance are less than the corresponding critical state values. It is concluded that the strength reduction that takes place from peak to post-rupture strength is due primarily to breakage of interparticle bonds, but that at higher confining pressures some particle orientation also takes place. Les résultats dessais oedométriques et triaxiaux sur des échantillons de bonne qualité et intacts, obtenus à partir de quatre argiles raides, non remaniées, sont présentés. Ces résultats sont comparés à ceux obtenus sur des argiles remaniées. ll est alors possible didentifier Iinfluence de la microstructure sur la compressibilité et la résistance au pic des argiles naturelles. Les quatre montrent une décroissance rapide de la résistance après le pic ainsi que des enveloppes de résistance post-rupture bien marquées. A des pressions de confinement faibles, les angles de résistance au cisaillement post-rupture sont tons proches des valeurs intrinseques critiques, mais certaines argiles présentent une faible coh6sion. A des pressions de confinement plus élevées, les angles de résistance au cisaillement post-rupture ont une valeur inférieure aux valeurs de ľétat critique correspondant. On peut donc conclure que la baisse de la résistance entre le pic et la résistance post-rupture est essentiellement due à la rupture de liaisons interparticulaires, mais que lorsque la pression de confinement est élevée, une réorganisation des particules pent aussi avoir lieu.
The response of two clayey sands to undrained cyclic triaxial loading is described. Both the stress history and the cyclic stress level have been varied. The behaviour is compared with that observed for the clayey sands tested under monotonic loading. Effective stress paths for the normally consolidated soils loaded monotonically in triaxial compression and extension are shown to form a hounding envelope which determines the pattern of behaviour under cyclic loading. A threshold strain is identified, below which cyclic straining results in stable behaviour. Above the threshold strain, pore pressures and strains accumulate under cyclic loading at a rate that increases as the effective stress state approaches the bounding envelope. On reaching the bounding envelope in triaxial compression, the clayey sands strain-soften. On reaching the bounding envelope in triaxial extension, there is liquefaction.
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