In this study, a vacuum and surcharge combined one-dimensional consolidation model is developed. Terzaghi's consolidation theory is revisited by applying the initial and boundary conditions corresponding to combined vacuum and surcharge loading on a soil. A test apparatus is designed, manufactured, and assembled to verify the model. The apparatus has the capacity of applying designated vacuum and surcharge pressures to a soil specimen, and it allows for the measurement of the excess pore-water pressure, settlement, and volume change during the consolidation process. Two series of tests are performed using the apparatus on two reconstituted natural clay soils, namely, the Welland sediment at water contents close to its liquid limit and the Orleans clay, reconstituted and consolidated under an effective stress of 60 kPa. The former test series mimics the strengthening of a very soft soil, such as the hydraulic fill used in land reclamation. The latter test series is designed to study vacuumsurcharge combined strengthening of a consolidated soil. It is demonstrated from the experiments that the one-dimensional vacuum-surcharge consolidation model describes the consolidation behaviour of both soils well. The consolidation characteristics of the soils show no discrimination against the nature of the consolidation pressure, namely, whether they are consolidated under the vacuum pressure alone, under the surcharge pressure alone, or under a pressure generated by the combined application of vacuum and surcharge. The study concluded that the soil consolidation characteristics obtained from the conventional consolidation tests can be used in the design of vacuum preloading systems, provided that the one-dimensional loading condition prevails.Key words: consolidation, soil improvement, vacuum pressure, surcharge pressure, excess pore-water pressure, soil consolidation parameters.
The effects of electrode materials and current intermittence on the coefficient of electro-osmotic permeability and the voltage loss at the soil-electrode interfaces are investigated using a marine soil. An electro-osmotic testing cell is designed and fabricated to measure the electro-osmotic induced flow under known boundary conditions. Six pairs of electrodes are tested for the voltage loss at the soil- electrode interfaces and for the coefficient of electroosmotic permeability. The losses in the applied voltage are found to be dependent on the anode material and are less in metallic anodes (steel or copper) than carbon anodes. The coefficients of electro-osmotic permeability are relatively independent of the electrode materials and are controlled by the effective electric field intensity in the soil. The application of current intermittence generates a higher electro-osmotic flow than continuous d.c. for the same applied voltage and the open electric circuit is superior to the short electric circuit configuration. The coefficient of electro-osmotic permeability is maximum using current intermittence of 2 min on/1 min off and open-circuit configuration for the soil tested. Nous étudions, en utilisant un sol marin, les effets des matériaux des électrodes et de l'intermittence de courant sur le coefficient de perméabilitéélectro-osmotique et la perte de tension aux interfaces sol-électrode. Nous avons conçu et fabriquéune cellule d'essai électro-osmotique pour mesurer le flux provoquépar électro-osmose en conditions limites connues. Nous testons six paires d'électrodes pour la perte de tension aux interfaces sol-électrodes et pour le coefficient de perméabilité électroosmotique. Nous constatons que les pertes de tension appliquée dépendent du matériau de l'anode et sont moindres avec les anodes métalliques (acier ou cuivre) qu'avec les anodes en carbone. Les coefficients de perméabilité électro-osmotique sont relativement indépendants du matériau de l'électrode et sont fonction de l'intensité du champ é lectrique effectif dans le sol. L'application d'un courant intermittent produit un flux é lectro-osmotique plus e levéque l'application d'un courant direct continu pour la même tension appliquée; et le circuit é lectrique ouvert est supérieur àla configuration de circuit é lectrique court. Le coefficient de perméabilitéé lectro-osmotique est à son maximum quand on utilise un courant intermittent activé pendant 2 minutes et désactivépendant 1 minute et une configuration à circuit ouvert pour le sol testé
In this study, the electrokinetics-generated pore fluid transport in an offshore calcareous soil is investigated in three steps. The pore fluid of the soil specimen tested has a salinity equivalent to that of seawater (artificial or Aseawater). The electroosmotic flow rates are measured for the A-seawater and two stabilizing permeating solutions, i.e., 15% CaCl 2 and 10% Al 2 (SO 4 ) 3 ·18H 2 O solutions. The results show that electroosmosis generated significant flow in the soil and can effectively transport the two permeating solutions through soil pores filled with A-seawater. The maximum flow rate is observed in the test conducted with 15% CaCl 2 solution, followed by those of A-seawater and 10% Al 2 (SO 4 ) 3 ·18H 2 O solutions, respectively. The results also show the significant role of electromigration in transporting the cations in the permeating solutions from the anode to the cathode. In particular, it is found that the electrokineticsgenerated ionic transport for calcium (Ca 2+ ) is 6.3 times faster than that for aluminum (Al 3+ ). The surface charge properties of the calcareous soil are studied by measuring the zeta potentials of the soil solids suspended in electrolyte solutions of various types, concentrations, and pH values. The relationship between the experimental and theoretical coefficients of electroosmotic permeability, k e , is examined based on the results from the electrokinetic experiments and the Helmholtz-Smoluchowski model. It is concluded that the effectiveness of electroosmosis in transporting water can be predicted qualitatively or semiquantitatively from the zeta potential of the soil solids suspension. The influence of pore fluid pH on the zeta potential of the soil is also investigated. The study provides important information for the use of electrokinetics to facilitate in situ artificial cementation of calcareous soils for offshore foundation applications.Résumé : Dans cette étude, on étudie en trois étapes le transport du fluide interstitiel généré par électrocinétique dans un sol calcaire offshore. Le fluide interstitiel du spécimen de sol testé a une salinité équivalente à l'eau de mer (artificielle ou eau de mer A). On a mesuré la vitesse d'écoulement électro-osmotique pour l'eau de mer A et pour deux solutions stabilisantes en percolation, i.e., 15% CaCl 2 et 10% Al 2 (SO 4 ) 3 ·18H 2 O. Les résultats montrent que l'électro-osmose génère un écoulement appréciable dans le sol et peut transporter de façon efficiente les deux solutions d'infiltrant à travers les pores du sol remplis d'eau de mer A. La vitesse d"écoulement maximale est observée dans l'essai fait avec une solution de 15% de CaCl 2 , suivie par celle de solutions d'eau de mer A et de 10% Al 2 (SO 4 ) 3 ·18H 2 O, respectivement. Les résultats montrent également le rôle significatif de l'électro-migration pour le transport des cations dans les solutions s'infiltrant de l'anode vers la cathode. En particulier, on trouve que l'électro-cinétique génère le transport ionique pour le calcium Ca 2+ 6,3 fois plus rapideme...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.