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The undrained shear strength of contractive fine-grained soils changes with time, reducing due to pore pressure generation and increasing during consolidation. There is an increasing appetite to recognise these temporal soil strength changes in offshore geotechnical design, as it provides a basis for potentially less conservative designs. Contributions to this endeavour are reported across two companion papers. This first paper extends an existing effective stress framework that relates the generation of pore pressure to accumulated plastic shear strain, allowing undrained shear strength to be calculated within the context of critical-state soil mechanics. The main development is the extension of the computational domain to two dimensions, allowing calculations to be made for boundary value problems that cannot be satisfactorily simplified to one-dimensional conditions. The magnitude and distribution of accumulated shear strain surrounding objects buried in soil are quantified through a series of large deformation finite element analyses. These spatial distributions are described using a strain influence function in the new 2D framework to calculate the extent and magnitude of excess pore pressure, and in turn the mobilised soil strength around the buried object. The performance of the 2D framework is examined in the companion paper through retrospective simulations of experimental and numerical data. [ABSTRACT FROM AUTHOR]

Plate anchors are an attractive technology for mooring floating facilities; as relative to piles, suction caissons, and drag anchors, they provide a much higher capacity relative to their mass. Plate anchors may experience an extreme loading event that will cause geotechnical failure, although they will still retain a residual capacity. The displacement associated with bringing the anchor to failure will induce excess pore pressures that initially reduce soil strength but will dissipate over time, leading to regains in soil strength and hence anchor capacity. This paper considers the time scales and magnitude of this anchor capacity regain through a series of model scale experiments conducted in a geotechnical centrifuge. The experiments involved vertical loading of pre-embedded horizontally orientated circular anchors in normally consolidated kaolin clay. The results show that anchor capacity regain is a function of consolidation time and the level of resistance maintained on the anchor, with the longest consolidation time and highest maintained resistance leading to a capacity regain of approximately 60%. These capacity increases are described here using a simple hyperbolic function, which provides a basis for estimating the time needed for the residual anchor capacity to regain sufficient capacity following a movement event. [ABSTRACT FROM AUTHOR]

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Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Many curve-fitting procedures based on the Terzaghi uncoupled consolidation theory have been proposed for determination of the laboratory coefficient of primary consolidation, c[sub v] . This paper presents data from 10 oedometer tests performed on clay samples from three different sites, with the c[sub v] values having been obtained using four different fitting procedures. The in situ settlements of the clay layers were measured using borehole extensometers. In this way the in situ c[sub v] values of the same clay were determined and compared with the laboratory values. At times, the four methods show considerable differences in the values of c[sub v] determined in the laboratory. Casagrande's method gives values that differ from those of the other methods and is not always easily usable. The other three methods provide a more consistent evaluation of the values c[sub v] . The comparison between in situ and laboratory c[sub v] values is not straight forward, since these findings show that the macrostructure of the soil layer influences the behaviour of the whole layer, and the laboratory c[sub v] values, apart from the method used for their determination, are sometimes unable to interpret settlement over time.Key words: clay, coefficient of primary consolidation, consolidation, embankment.Plusieurs procédures de lissage de courbes basées sur la théorie de consolidation découplée de Terzaghi ont été proposées pour déterminer le coefficient de consolidation primaire c[sub v] , Cet article utilise des données provenant de dix essais oedométriques réalisés sur des échantillons d'argile provenant de trois sites différents, et des valeurs de c[sub v] ayant été obtenues au moyen de quatre différentes procédures de lissage comparées entre elles. De plus, les tassements in sltu des couches d'argile ont été mesurés au moyen d'extensomètres dans des forages. Ainsi, les valeurs de c[sub v] in situ de la même argile qui a été testée en laboratoire ont été déterminées et comparées avec les valeurs obtenues en laboratoire. Parfois, les quatre méthodes ont montré des différences considérables dans la détermination de c[sub v] en laboratoire. La méthode de Casagrande donne des valeurs qui diffèrent des autres méthodes et n'est pas toujours facile à utiliser. Les trois autres méthodes montrent une évaluation plus consistante des valeurs puisque le rapport entre deux de ces valeurs présente un rapport plus constant. La comparaison entre les valeurs de c[sub v] in situ et en laboratoire n'est pas toujours simple puisque les valeurs obtenues montrent que la microstructure de la couche d'argile influence le comportement de l'ensemble de la couche, et les valeurs de c[sub v] en laboratoire, quelle que soit la méthode utilisée pour leur détermination, ne permettent pas parfois d'interpréter le tassement en fonction du temps.Mots clés : argile, coefficient de consolidation primaire, consolidation, remblai.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

To analyze the effects of strain rate and viscoplastic strain on consolidation of natural clay, this paper presents a nonlinear viscoplastic model in which viscoplastic behaviour is modeled by a unique effective stress (σ'[sub v] ) – viscous strain (ℇ[sub v] ) – viscous strain rate (ℇ[sup ·] [sub v] ) relationship. The proposed model can consider the effects of strain rate and viscoplastic strain on consolidation, to take into account the difference in strain rate between laboratory and field conditions, and the combined processes of generation and dissipation of pore pressure during consolidation. This model can also predict the behaviour of clay during stepwise loading, constant rate of strain, and relaxation of effective stress. The predicted values using numerical analysis are compared with measured values in laboratory tests and in situ, under an embankment built on soft clay at Berthierville, Quebec. It is possible to estimate the consolidation behaviour of natural clay with reasonable accuracy using the proposed nonlinear viscoplastic model.Key words: consolidation, soft clay, strain rate, viscoplastic, relaxation.Dans le but d'analyser les effets de la vitesse de déformation et de la déformation viscoplastique sur la consolidation de l'argile naturelle, cet article présente un modèle viscoplastique non linéaire dans lequel le comportement est modélisé par une relation unique contrainte effective-déformation visqueuse-vitesse de déformation visqueuse σ'[sub v] – ℇ[sub v] – ℇ[sup ·] [sub v] . Le modèle proposé peut prendre en considération les effets de la vitesse de déformation et de la déformation viscoplastique sur la consolidation pour tenir compte de la différence dans les vitesses de déformation entre les conditions en laboratoire et sur le chantier, de même que les processus combinés de génération et de dissipation de la pression interstitielle durant la consolidation. Ce modèle peut aussi prédire le comportement de l'argile en incluant le chargement par étape, la vitesse de déformation constante, et la relaxation de la contrainte effective. Les valeurs prédites au moyen de l'analyse numérique sont comparées avec celles mesurées dans les essais en laboratoire et in situ sous un remblai construit sur de l'argile molle à Berthierville, Québec. Il est possible d'estimer le comportement en consolidation de l'argile naturelle avec une précision raisonnable au moyen du modèle viscoplastique non linéaire proposé. Mots clés : consolidation, argile molle, vitesse de déformation, viscoplastique, relaxation.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

Using settlement observations published for several embankments on marine clays of the Champlain Sea, an empirical model is proposed to estimate long-term settlements. The effect of the overconsolidation ratio is taken into consideration within the model. Footing- and raft-type foundation cases are considered to give guidelines when using the model for these foundation types. A specific embankment resting on a foundation of high water content clay with a high compressibility index demonstrates that a correction factor should be applied under these conditions.Key words: settlement, embankment, Champlain Sea clay, consolidation, empirical model.À l'aide de mesures de tassements publiées pour plusieurs remblais assis sur les argiles de la mer Champlain, un modèle empirique visant à estimer les tassements à long terme est proposé. L'effet du rapport de surconsolidation est pris en considération à l'intérieur du modèle. Quelques cas d'empattements et de radiers sont aussi considérés afin de préciser l'utilisation du modèle pour ces types de fondation. Le cas précis d'un remblai assis sur une argile à forte teneur en eau et ayant un indice de compressibilité élevé démontre qu'un facteur de correction doit s'appliquer dans ces conditions.Mots clés : tassement, remblais, argile de la mer Champlain, consolidation, modèle empirique. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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 vacuum–surcharge 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.Dans cette étude, on développe un modèle de consolidation unidimensionnelle par l'application combinée du vide et d'une surcharge. La théorie de consolidation de Terzaghi est révisée en appliquant les conditions aux frontières et initiales correspondant à une combinaison de chargement par vide et par surcharge. Un appareil d'essai est conçu, fabriqué et assemblé pour vérifier le modèle. L'appareil peut appliquer à un spécimen de sol des pressions de vide et de surcharge choisies, et permet la mesure de l'excédent de pression interstitielle, du tassement et du changement de volume durant le processus de consolidation. Deux séries d'essais ont été réalisés au moyen de l'appareil sur deux sols argileux naturels reconstitués, nommément le sédiment de Welland à des teneurs en eau près de la limite de liquidité, et l'argile d'Orléans, reconstitués et consolidés sous une pression effective de 60 kPa. La première série d"essais simule le renforcement d'un sol très mou tel qu'un remblai hydraulique utilisé dans la réhabilitation des terrains. La deuxième série d'essais est conçue pour étudier le renforcement d'un sol consolidé par la combinaison du vide et de la surcharge. En partant de ces expériences, on démontre que le modèle de consolidation unidimensionnelle par vide-surcharge décrit bien le comportement de consolidation des sols. Les caractéristiques de consolidation des sols ne montrent aucune distinction en fonction de la nature de la pression de consolidation, nommément, qu'elle soit générée par le vide seulement, par une surcharge, ou par une combinaison de vide et de surcharge. L'étude à conclu que les caractéristiques de consolidation obtenues par des essais conventionnels de consolidation peuvent être utilisées dans la conception de systèmes de préchargement sous vide, pourvu que la condition unidimensionnelle de chargement prévale.Mots clés : amélioration du sol, pression de vide, pression de surcharge, excédent de pression interstitielle, paramètres de consolidation du sol.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

The present research concerns a comparative analysis of the possible methods for estimating soft silty clay permeability to be used in the analysis of consolidation. For this purpose the consolidation response of a thick and homogeneous, instrumented soft silty clay deposit, on which an embankment was constructed, is back-analyzed using the finite-element method. To model the consolidation process, permeability data are carefully determined both from laboratory and in situ piezocone tests. One-dimensional and triaxial permeability test data are compared with the results of piezocone dissipation tests, the latter interpreted using four different solutions. The effects of anisotropy on permeability characteristics influencing the consolidation rate are also discussed.Key words: consolidation, embankment, finite-element analyses, permeability, piezocone, soft silty clay.La présente recherche traite d'une analyse comparative des méthodes possibles pour évaluer la perméabilité devant être utilisée dans l'analyse de la consolidation de l'argile limoneuse molle. À cette fin, on analyse à rebours au moyen de la méthode d'éléments finis la réponse en consolidation d'un dépôt instrumenté épais et homogène d'argile limoneuse molle sur lequel un remblai a été construit. Afin de modéliser le processus de consolidation, les données de perméabilité sont déterminées minutieusement au moyen d'essais en laboratoire et d'essais de piézocône in situ. Les données d'essais de perméabilité unidimensionnels et triaxiaux sont comparées avec les résultats des essais de dissipation au piézocône qui ont été interprétés au moyen de différentes solutions. On discute également les effets de l'anisotropie sur les caractéristiques de perméabilité influençant la vitesse de consolidation.Mots clés : consolidation, remblai, analyse en éléments finis, perméabilité, piézocône, argile limoneuse molle. [Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

The behaviour of geosynthetic-reinforced embankments constructed over soft cohesive soils installed with prefabricated vertical drains (PVDs) is investigated by numerically examining an embankment constructed over different foundation soils. The partial consolidation during embankment construction, the consequent shear strength gain of the foundation soil, and the effect of the use of reinforcement on the mobilization of shear strength are examined. It is shown that the combined use of reinforcement and PVDs can significantly increase embankment stability and potentially allow the rapid construction of higher embankments than could be achieved with either method of soil improvement alone. Construction rate and spacing of PVDs can significantly affect the degree of consolidation at the end of construction and the stability of the embankment. For the situation examined, the effect of well resistance of typical vertical drains is insignificant. A relatively simple method for calculating the degree of consolidation and the strength gain of the foundation soil during construction is evaluated based on finite element results and is shown to be reasonably conservative. A design procedure is proposed to combine the design of reinforcement and PVDs.Key words: soft clay, prefabricated vertical drain, reinforcement, embankment stability, consolidation, strength gain.Le comportement de remblais armés de géosynthétiques construits sur des sols mous cohérents équipés de drains verticaux préfabriqués (PVD) est étudié au moyen d'un examen numérique d'un remblai construit sur différents sols de fondation. On examine la consolidation partielle durant la construction du remblai, le gain de résistance au cisaillement du sol de fondation qui en découle, et l'effet de l'utilisation de l'armature sur la mobilisation de la résistance au cisaillement. Il est montré que l'utilisation combinée de l'armature et des PVD peut augmenter appréciablement la stabilité du remblai, et permettre potentiellement la construction rapide de remblais plus hauts que ceux qui pourraient être réalisés avec seulement l'une ou l'autre des méthodes d'amélioration. La vitesse de construction et l'espacement des PVD peuvent influencer appréciablement le degré de consolidation à la fin de la construction et la stabilité du remblai. Dans le cas étudié, l'effet de la résistance des drains verticaux est négligeable. Une méthode relativement simple de calcul du degré de consolidation et du gain de résistance du sol de fondation durant la construction est évaluée en partant des résultats d'éléments finis et s'est avérée être raisonnablement conservatrice. On propose une procédure de calcul pour combiner la conception de l'armature et des drains PVD.Mots clés : argile molle, drains verticaux préfabriqués, armature, stabilité de remblai, consolidation, gain de résistance.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

A pilot test was carried out at a land reclamation project site to study the effect of vertical drains on the rate of consolidation of a marine clay deposit in Singapore. Theoretical and numerical analyses were conducted to interpret the field measurements of pore pressure and settlement, and consolidation parameters were back-calculated. The back-calculated preconsolidation pressure is similar to that obtained from the laboratory consolidation test on undisturbed samples, but the field-deduced compression index is generally larger than that measured in the laboratory. The coefficient of consolidation back-calculated from the settlement measurement is larger than that from the pore-pressure measurement. The coefficient of consolidation for horizontal flow obtained from the Rowe cell test, which is comparable to that back-calculated from the field settlement measurement, is recommended for the preliminary design of vertical drains without the need of considering the smear effect.Key words: clays, consolidation, ground improvement, numerical modelling and analysis, permeability, vertical drains.Un essai pilote a été réalisé sur le site d'un projet de réhabilitation de terrain pour étudier l'effet des drains verticaux sur la vitesse de consolidation d'un dépôt d'argile marine à Singapore. Des analyses théorique et numérique ont été réalisées pour interpréter les mesures sur le terrain de la pression interstitielle et du tassement, et des paramètres de consolidation ont été calculés à rebours. La pression de consolidation calculée à rebours est similaire à celle obtenue par l'essai de consolidation en laboratoire sur des échantillons non remaniés, mais l'indice de compression déduit du terrain est généralement plus grand que celui mesuré en laboratoire. Le coefficient de consolidation calculé à rebours à partir des mesures de tassement est plus grand que celui obtenu par la mesure de la pression interstitielle. Le coefficient de consolidation pour l'écoulement horizontal obtenu par l'essai avec la cellule de Rowe, qui est comparable à celui calculé à rebours à partir de la mesure du tassement sur le terrain, est recommandé pour la conception préliminaire des drains verticaux sans prendre en compte l'effet de souillure d'argile remaniée.Mots clés : argiles, consolidation, amélioration des terrains, modélisation et analyse numériques, perméabilité, drains verticaux.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]