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An experimental study of the behaviour of sands under generalized drainage boundary conditions is presented. The influence of partially drained conditions, which generally is a reflection of the loading rate and the permeability of the soil, has been studied by limiting the volumetric deformation between drained and undrained states. The effect of potential pore-pressure variations in situ has been assessed by simulating various levels of volumetric deformation during shear. Conventional drained and undrained tests were also carried out on the same sands to enable a direct evaluation of the effect of drainage. A triaxial device with the ability to control strain-paths was used to carry out the tests, and all tests were performed under compression loading with no change in total lateral stress. A systematic change in the stress-strain response was noted as the drainage conditions gradually change from drained to undrained. The maximum excess pore pressure generated owing to inhibition of drainage is almost linearly related to the amount of drainage blocked. These results support the contention that the undrained state may not represent the most damaging scenario under field loading conditions. Much smaller minimum shear strength values compared with the undrained strength were measured when pore-pressure boundary conditions caused expansive volume changes. The domain of strain-softening response, and hence liquefaction susceptibility, increased owing to such loading. Résumé :On présente une étude expérimentale du comportement des sables dans des conditions généralisées de drainage aux frontières. On a étudié l'influence des conditions partiellement drainées, qui s'explique généralement par la vitesse de chargement et la perméabilité du sol, en limitant la déformation volumétrique entre les états drainés et non drainés. L'effet des variations potentielles de la pression interstitielle in situ a été évalué en simulant divers niveaux de déformation volumétrique au cours du cisaillement. On a aussi fait des essais traditionnels drainés et non drainés sur les mêmes sables pour permettre une évaluation directe de l'effet du drainage. Un appareil triaxial à cheminement de contrainte contrôlé a été utilisé lors des essais, et tous les essais ont été effectués sous un effort de compression sans changement aux contraintes latérales totales. On a observé un changement systématique de la réponse contraintedéformation lorsque les conditions de drainage changeaient graduellement de drainées à non drainées. L'excédent maximum de pression interstitielle généré dû à l'inhibition du drainage est presque en relation linéaire avec la quantité de drainage bloqué. Ces résultats appuient la contention que l'état non drainé peut ne pas représenter le scénario le plus dommageable dans les conditions de chargement sur le terrain. On a mesuré des valeurs minimales de résistance au cisaillement beaucoup plus petites que celles de la résistance non drainée lorsque les conditions de pression interstitielle aux frontières produisaient des chang...

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An experimental study of the behaviour of an alluvial sand under different strain increment paths representing shear–volume coupled deformation is presented. Both pore pressure and pore volume change simultaneously in these tests. Linear strain paths with different levels of limiting volumetric strain and nonlinear strain paths that simulate different pore pressure boundary conditions were applied to the soil specimen in the laboratory. The strain paths imposed included both expansive and contractive volumetric deformation. Nonuniform excess pore pressures generated during earthquakes (on account of the heterogeneity in natural soils) often lead to such deformation in situ following the end of strong shaking. The shear strength of the soil could decrease significantly when the pore pressure boundary conditions result in volume inflow that leads to a considerable reduction of the effective confining stress. The rate of volume inflow plays a significant role on the resulting stress–strain and pore pressure responses. Both the peak and the minimum shear strength mobilized during the test were significantly dependent on the strain path. The effective stress ratio at the instant of peak pore pressure is independent of the strain path followed, and it is equal to the effective stress ratio noted at the instant of phase transformation in undrained tests.