Composite clay is a mixture of clay, as the main body, and aggregates, which are floating within the clayey matrix. The undrained behavior of composite clay in its natural or compacted state, e.g., core material of embankment dams, has great importance for geotechnical engineers. An extensive test program was conducted on kaolin-gravel and kaolin-sand mixtures to investigate various effects of aggregates on the mechanical behavior of the mixtures during strain-controlled monotonic and cyclic loadings. Monotonic test results reveal that increasing the aggregate content leads to a gradual increase in shear strength. Meanwhile, when the aggregate content is raised, the pore pressure increases for both monotonic and cyclic loading. It is also found that the presence of aggregates within a cohesive matrix leads to formation of a heterogeneous matrix in the clayey part of composite clays. This heterogeneity in turn causes pore pressure to be increased with an increase in the aggregate content during both monotonic and cyclic loading. In addition, test results show that aggregate size does not influence mechanical behavior appreciably. The results of this experimental research program are presented and discussed in this paper.Résumé : L'argile composite est un mélange constitué d'argile comme composante principale et d'agrégats qui flottent dans la matrice argileuse. Le comportement non drainé des argiles composites dans leur état naturel ou tassé, par. ex., matériau du noyau des barrages en terre, a une grande importance pour les ingénieurs géotechniciens. Un programme d'essais élaboré a été conduit sur les mélanges kaolin-gravier et kaolin-sable pour étudier divers effets de l'agrégat sur le comportement mécanique des mélanges durant les chargements monotoniques et cycliques à déformation contrôlée. Les résultats des essais monotoniques ont révélé que la résistance au cisaillement augmente avec l'augmentation de la teneur en agrégats. En même temps, lorsque la teneur en agrégats est augmentée, la pression interstitielle augmente pour les chargements monotoniques de même que cycliques. On trouve également que la présence des agrégats dans la matrice cohérente conduit à la formation d'une matrice hétérogène dans la partie argileuse des argiles composites. À son tour, l'hétérogénéité produit une augmentation de la pression interstitielle avec l'augmentation de la teneur en agré-gats durant les chargements tant monotoniques que cycliques. De plus, les résultats des essais montrent que la grosseur des agrégats influence appréciablement le comportement mécanique. Dans cet article, on présente et discute les résul-tats de ce programme de recherche expérimental.
The performance of a geologic carbon storage site strongly depends on the capillary pressure of sealing rock and formations. While wettability of minerals is a key factor in capillary pressure, published contact angles are inconsistent. This study explores the discrepancy of published contact angles in order to reduce the uncertainty of measured laboratory contact angles, and understand the variation of contact angles at unsaturated CO 2 -water conditions. A ratio of droplet dimension and triple line (or contact line) are used to explain the observed wide range of contact angles and the variation of contact angle at unsaturated conditions. Results show that the shape factor has a good agreement with contact angle change during CO 2 dissolution in water. Silica substrate has clear two pinned and slip stages of triple line during CO 2 droplet dissolution, which cause contact angle on silica substrate to increase from 34.58 to 42.18. However, mica substrate has the repeated pinned and slip stages due to the heterogeneity of mica surface, which cause contact angle to increase dramatically from 25.48 to 68.18. Thus, both the impact of the unsaturated CO 2 -water conditions on the wide range of contact angle and the heterogeneity of mineral surface should be considered when one estimates capillary pressure based on contact angle in geological CO 2 sequestration.
R( 1) where P C is capillary pressure, P CO2 is CO 2 pressure, P water is water pressure, c CO2-water is the water-CO 2 interfacial tension, h is the water contact angle on mineral surface, and R is pore radius.
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