Search

A series of one-dimensional cation infiltration tests under different drainage/infiltration conditions, infiltration times, ion concentrations ([Na.sup.+]), and vertical stresses were performed to comprehensively understand the osmotic consolidation of bentonite. The local behaviour of the specimen was captured on a digital camera through a transparent acrylic oedometer ring by tracking the movements of the marker sands on the side of the specimen. The [Na.sup.+] concentration of the pore fluid throughout the specimen was measured after the test to investigate the spatiotemporal relationships between consolidation behaviour and cation infiltration. In the initial period of infiltration, the pore water pressure measured at the undrained bottom increased. A local swelling behaviour inside the specimen was observed during osmotic consolidation. The low permeability of expansive soils obstructs osmotically induced water drainage from the interlayer space of the expansive clay mineral, especially in regions far from the drainage boundary. This transition of pore water pressure affects the local mechanical behaviour; the dissipation of pore water pressure is followed by settlement. Therefore, the process of osmotic consolidation is totally longer than that of pure mechanical consolidation. Key words: expansive clay, osmotic consolidation, soil infiltration, cation concentration, bentonite, Introduction Expansive clays are investigated as a possible buffer material for radioactive wastes (e.g., Delage et al. 2010). However, these soils in actual ground cause slope failure, infrastructural damage, etc. [...]

It has recently been shown that the overall deformation characteristics of granular materials during liquefaction seems to be governed by local void ratio characteristics. The aim of this study is to investigate the relationship between mechanical properties and local void ratio changes during liquefaction in two materials of different weights (aluminium-type and plastic-type rod assemblies). A series of constant-volume cyclic bi-axial loading tests was conducted together with the image analysis obtaining local void behaviour. The experimental results demonstrate that the first liquefaction resistance of the plastic sample is higher than the aluminium one, corresponding to its smaller initial void ratio and less contractive behaviour observed in the early stage of drained monotonic compression. However, after experiencing the first liquefaction and subsequent re-consolidation histories, a liquefiable assembly of aluminium and plastic rods both became either denser (densification) or more homogenous (homogenization) in terms of local void ratio, suggesting an increase in liquefaction resistance in the next liquefaction stage. This work also includes a preliminary analogous study using a semi-3D discrete element method (DEM) with one single layer of spherical particles to simulate the similar liquefaction behaviour observed in the laboratory tests.

The strength and deformation characteristics of compacted soils are typically evaluated using triaxial compression tests on specimens that are compacted relatively uniformly in a laboratory. Soil compacted in the field using vibration rollers is nonuniform in the vertical depth direction; this is because the gradient of the dry density and saturation degree in the depth direction of each compaction layer is large, owing to the distribution of the load transmitted from the contact surface. As a quality control method for earth-filling works, nondestructive inspection indices—such as the soil stiffness index—are applied in some cases, and the average value of the nonuniform compaction layers is measured. Further, unsaturated specimens, which were retrieved from the test fill yielded during field compaction tests, and specimens obtained via compaction using the same soil as that in the laboratory were prepared, and then triaxial compression tests were performed. Local displacement transducers were installed to obtain local deformation characteristics, based on the vertical depth of the specimen, which were then compared with the average deformation characteristics of the entire specimen. The results show that the local low-stiffness section significantly affects the overall average; this makes it non-negligible because the specimen compacted in the field is nonuniform. However, because field-compacted soil has a local lowstiffness section near the surface layer compared with laboratory-compacted soil, evaluations based on the nondestructive inspection of the surface layer may result in underestimations.

Evaluations of water retention characteristics of typical iron ore fines (IOF) were presented, which was part of experimental works for the estimation of liquefaction potential of IOF heaps. The water retention tests were conducted in a suction range from 0.1 to [10.sup.6] kPa on two IOFs and two artificial soils with various testing techniques. It is observed that water retention characteristic curves of one IOF (IOF-B) converge in terms of the relationship between suction (S) and water content (w) regardless densities of specimens when S exceeds a threshold value ([S.sub.th]). Based on this finding, water retention characteristics are divided into density and materials affected zones. It is also found that IOFs generally have higher water retention ability than the two artificial soils, from which discussion is made on the effect of specific surface area and mineralogy on water retention characteristics of IOF. Finally, water retention characteristics are linked to compaction curves, from which, with the consideration that degree of saturation at peaks of compaction curves is relatively constant, a safety margin of a recently proposed regulation for maritime transportation of IOF is discussed. Key words: iron ore fines, water retention characteristics, suction-volumetric water ratio relationship, compaction. Des evaluations de caracteristiques de retention d'eau de fines de minerai de fer (<< IOF >>) typiques ont ete presentees, ce qui faisait partie des travaux experimentaux d'estimation du potentiel de liquefaction de tas d'IOF. Les essais de retention d'eau ont ete realises dans une gamme de succion de 0,1 a [10.sup.6] kPa sur deux IOF et deux sols artificiels en utilisant differentes techniques d'essais. On observe que les courbes de caracteristiques de retention d'eau d'un IOF (IOF-B) convergent en termes de relation entre la succion (S) et la teneur en eau (w) independamment des densites des echantillons lorsque S depasse une valeur seuil ([S.sub.th]). Sur la base de ces resultats, les caracteristiques de retention d'eau sont divisees en zones affectees par la densite et les materiaux. On constate egalement que les IOF ont generalement une capacite de retention d'eau superieure a celle des deux sols artificiels, d'ou il est question de l'effet de la surface specifique et de la mineralogie sur les caracteristiques de retention d'eau de l'IOF. Enfin, les caracteristiques de retention d'eau sont liees aux courbes de compactage, a partir desquelles, compte tenu du fait que le degre de saturation aux pointes des courbes de compactage est relativement constant, une marge de securite d'un reglement recemment propose pour le transport maritime des IOF est examinee. [Traduit par la Redaction] Mots-cles: fines de minerai de fer, caracteristiques de retention d'eau, rapport succion-humidite volumique, compactage., Introduction Iron ore fines (IOF) is a type of bulk cargoes commonly transported at sea. In 2009, casualties of two vessels loaded IOF happened near Indian ports (IMO 2010a, 2010b). [...]

The main purpose of the presented paper is to show the advantages and disadvantages of evaluating the small strain stiffness of cohesionless soils by means of different types of laboratory equipment. A series of consolidated undrained cyclic triaxial testes have been performed on saturated specimens made of Toyoura sand and Sofia sand having various dry densities. Relatively small unloading-reloading cycles have been applied on the specimens in order to obtain the 'static' Young's modulus. Furthermore two types of wave propagation techniques have been adopted for the sake of a 'dynamic' Young's modulus determination: one is using bender elements in the cross section of the specimen and the other is using trigger elements in the longitudinal section of the specimen to excite shear waves and two accelerometers which capture the waves' arrival in two points. On one hand the difference between the two types of dynamic measurements and static measurements is discussed and on the other hand some relationships between the abovementioned approaches are given.

Concerning the static liquefaction properties of an industrial cargo, i.e., iron ore fines (IOF), undrained monotonie behaviors of a type of IOF are revealed through conducting triaxial compression tests. It is found that IOF exhibit some similar behaviors as those of common sandy soils, while some very unusual behaviors are also observed. All IOF specimens with compaction degree of 84%-95% and confining pressure of 50-200 kPa exhibit dilative behavior from the beginning of axial loading until the deviator stresses reach their peaks ([q.sub.pk]). Then the dilative behavior transforms to a contractive behavior, and the contractive behavior continues until reaching the residual stress without observation of phase transformation and quasi steady state. These behaviors are not usually observed for common sandy soils based on extensive previous works. More studies may be necessary as these unusual behaviors imply that flow failure, similar to the undrained monotonic behavior of very loose sand, may be triggered regardless of the density of IOF. In addition, this study also establishes the relationships of IOF between its initial conditions, peak stress conditions, and residual conditions by employing classical knowledges developed for sandy soils. Key words: iron ore fines, undrained triaxial test, static liquefaction, steady state, collapse surface. En ce qui concerne les proprietes de liquefaction statique d'une marchandise industrielle, les fins minerais de fer (<< IOF >>), les comportements monotones non draines d'un type d'IOF sont reveles par des essais de compression triaxiale. Il est constate que les IOF presentent des comportements similaires a ceux des sols sableux communs, alors que certains comportements tres inhabituels sont egalement observes. Tous les specimens IOF avec un degre de compaction de 84-95 % et une pression de confinement de 50-200 kPa presentent un comportement dilatatif depuis le debut du chargement axial jusqu'a ce que les contraintes de deviateur atteignent leurs maximums ([q.sub.pk]). Le comportement dilatatif se transforme ensuite en comportement contractif, et le comportement de contraction continue jusqu'a atteindre la contrainte residuelle sans observation de transformation de phase et d'etat quasi d'equilibre. Ces comportements ne sont generalement pas observes pour les sols sablonneux communs sur la base d'importants travaux anterieurs. D'autres recherches peuvent etre necessaires, car ces comportements inhabituels impliquent que la defaillance de l'ecoulement, similaire au comportement monotone non draine du sable tres lache, peut etre declenchee independamment de la densite de l'IOF. En outre, cette recherche etablit egalement les relations de l'IOF entre ses conditions initiales, les conditions de contrainte maximale et les conditions residuelles en utilisant les connaissances classiques developpees pour les sols sableux. Mots-cles : fins minerais de fer, essai triaxial non draine, liquefaction statique, etat d'equilibre, surface d'effondrement., Introduction Iron ore fines (IOF) are transported as a type of bulk cargo for the iron-making industry. Together with some other cargoes, such as nickel ore and sinter feed bauxite, [...]