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This paper reports advanced three-dimensional large-deformation finite element analyses investigating the effect of the padeye offset on the behaviour of plate anchors. The analyses varied the normalized padeye offset from 0 to 0.5 and identified two counterbalancing effects on the anchor bearing capacity induced by the padeye offset. These are the change in anchor inclination with respect to the direction of loading (detrimental due to the reduction of bearing area) and the reduction of loss of embedment (beneficial, as the anchor mobilizes stronger soil). The results provide insights to optimize the design of plate anchors. The underlying concepts also have applications for other types of anchors. Key words: plate anchor, large-deformation finite element analysis, clays, offshore engineering, loss of embedment, bearing capacity. Cet article presente des analyses par elements finis avancees en trois dimensions et en grande deformation servant a etudier l'effet de l'espacement des mains de fer sur le comportement des ancrages fi plaque. Les analyses ont fait varier l'espacement normalise des mains de fer de 0 a 0,5 et a identifie deux effets contre-balanciers sur la capacite portante des ancrages causes par l'espacement des mains de fer. Il s'agit de la variation de l'inclinaison de l'ancrage selon la direction de la charge (effet negatif du a la reduction de la surface portante) et de la reduction des pertes d'enfouissement (benefique puisque l'ancrage mobilise un sol plus fort). Ces resultats offre des informations pour optimiser la conception des ancrages a plaque. Les concepts de base ont aussi des applications pour d'autres types d'ancrage. [Traduit par la Redaction] Mots-cles: ancrage fi plaque, analyse par elements finis en grande deformation, argiles, ingenierie en mer, perte d'enfouissement, capacite portante., Introduction Plate anchors are an economic and efficient deep-water mooring solution, which have been used increasingly in recent years (Dove et al. 1998; Murff et al. 2005; Yang et al. [...]

Shallow skirted foundations can mobilize uplift resistance from end bearing in the short to medium term. However, uncertainty exists over the magnitude of reverse end bearing resistance compared with resistance in compression, and how this might be affected by a gap between the external face of the foundation skirt and the adjacent soil. The study presented in this paper explores this problem through centrifuge model tests, investigating the effect of skirt embedment ratio on (i) the magnitude of reverse end bearing capacity compared with compression capacity, (ii) the uplift displacement associated with spontaneous loss of suction during uplift, and (iii) the existence of a vertical gap along the external skirt-soil interface. The results show that (i) peak uplift capacity equivalent to compression capacity can be mobilized for a fully sealed foundation with an intact skirt-soil interface, (ii) suction required for reverse end bearing can be maintained through considerable foundation displacement, even for a low skirt embedment ratio, and (iii) the presence of a vertical gap along the external skirt-soil interface causes abrupt loss of suction beneath the top plate after minimal foundation displacement, with subsequent uplift capacity being markedly reduced. Key words: bearing capacity, centrifuge modelling, clays, footings-foundations, offshore engineering, suction. Les fondations chemisees peu profondes peuvent mobiliser de la resistance au soulevement a une extremite sur une periode de temps courte et moyenne. Cependant, il y a des incertitudes en lien avec la magnitude de la resistance a l'extremite inverse comparativement a la resistance en compression, ainsi que la facon dont cette magnitude est affectee par l'espace entre la face externe de la chemise de la fondation et le sol adjacent. L'etude presentee dans cet article explore cette problematique a l'aide d'essais de modelisation par centrifugeuse servant a evaluer l'effet du ratio d'ancrage de la chemise sur (i) la magnitude de la capacite portante de l'extremite inverse comparativement a la capacite en compression, (ii) le deplacement en soulevement associe a la perte de succion spontanee durant le soulevement et (iii) l'existence d'un espace vertical sur l'interface externe entre la chemise et le sol. Les resultats demontrent que (i) une capacite de soulevement maximale equivalente a la capacite en compression peut etre mobilisee dans le cas d'une fondation completement scellee avec un interface chemise-sol intact, (ii)la succion necessaire pour la capacite portante de l'extremite inverse peut etre maintenue malgre des deplacements considerables de la fondation, meme pour un faible ratio d'ancrage de la chemise et (iii) la presence d'un espace vertical le long de l'interface externe chemise-sol entrame une perte de succion abrupte sous la plaque superieure suite a un deplacement minimal de la fondation, et la capacite de soulevement est reduite significativement par la suite. [Traduit par la Redaction] Mots-cles: capacite portante, modelisation par centrifugeuse, argiles, semelles/fondations, ingenierie en mer, succion., Introduction Skirted foundations Skirted foundations comprise a top plate with a peripheral 'skirt'. The skirt penetrates the seabed until the top plate comes into contact with the seabed, confining a [...]

Current design practice for pipe-seabed interaction in soft soils is generally based on the assumption of undrained behaviour throughout laying and subsequent operation. In reality, drainage and consolidation around a partially embedded pipe can have a marked effect on the vertical penetration and horizontal breakout resistance. In this paper, a large-deformation finite element methodology coupled with the 'modified Cam clay' plasticity soil model has been developed to study the coupled consolidation behaviour of soil around partially embedded seabed pipelines. Simulations of penetration show that after laying, subsequent consolidation leads to further embedment by an amount dependent on the level of drainage that occurred during laying. Also, if the pipe is embedded under undrained conditions, the waiting period between laying and operation allows the soil around the pipe to consolidate under the pipe self-weight. The consolidation process results in an increase in the strength of the soil. The lateral breakout resistance and the direction of pipe movement on breakout thus depend on the consolidated strength of the soil around the pipe, as well as the applied loading. The envelopes of vertical-lateral combined loading bearing capacity differ markedly from those predicted assuming undrained behaviour throughout. Key words: pipeline, offshore engineering, clay, consolidation, penetration, finite element method. La pratique courante de conception de l'interaction tuyau-fond marin est generalement basee sur l'hypothese d'un comportement non draine durant le placement et durant l'operation subsequente. En realite, le drainage et la consolidation autour d'un tuyau partiellement enfoui peut avoir un effet marque sur la penetration verticale et la resistance horizontale a la separation. Dans cet article, une methodologie par elements finis a grande deformation couplee avec le modele de plasticite du sol << Cam clay modifie >> a ete developpee pour etudier le comportement couple en consolidation du sol autour de tuyaux partiellement enfouis dans le fond marin. Des simulations de penetration montrent que suite a la deposition, la consolidation subsequente entrame un enfouissement supplementaire dependamment du niveau de drainage s'etant produit durant la deposition. De plus, si le tuyau est enfoui en conditions non drainees, la periode d'attente entre la deposition et l'operation permet au sol autour du tuyau de consolider sous le poids du tuyau. Le processus de consolidation resulte en une augmentation de la resistance du sol. La resistance a la separation laterale et la direction du mouvement du tuyau lors de la separation dependent ainsi de la resistance a la consolidation du sol autour du tuyau, de meme que sur la charge appliquee. Les enveloppes de capacite portante en sollicitations verticales-laterales combinees different de faon marquee de celles predites en supposant un comportement non draine. [Traduit par la Redaction] Mots-cles: tuyau, ingenierie en mer, argile, consolidation, penetration, methode par elements finis., Introduction When offshore oil and gas reserves are exploited in deep-water, long pipelines are required within each field and are often used to transport the hydrocarbons to shore. In shallow [...]

Offshore developments for hydrocarbon resources have now progressed to water depths approaching 3000 m, with geotechnical design increasingly focused on soft sediments in the upper 30 m or so of the seabed. Due to the difficulties and high cost in recovering high-quality samples from deepwater sites, there is increasing dependence on in situ testing techniques for determining the geotechnical design parameters. This paper summarizes the findings from a joint industry project, undertaken by the Norwegian Geotechnical Institute and the Centre for Offshore Foundation Systems at The University of Western Australia, on the use of in situ testing for the characterization of deepwater soft soils. The project focused on theoretical and empirical studies for the interpretation of piezocone, T-bar, and ball penetration test data, linking the penetration resistance to shear strengths determined from in situ vane tests and laboratory tests on high-quality samples. Guidelines are summarized for interpreting in situ test data, particularly for estimating intact and remoulded undrained shear strengths from the penetration resistance measured by each type of penetrometer. Suggestions are also given for future development of in situ testing techniques to maximize the potential of in situ testing in characterization of deepwater soft soils. Key words: offshore soil investigations, soft clay, full flow penetrations, undrained shear strength. Les developpements des ressources d'hydrocarbures en mer atteignent maintenant des profondeurs de pres de 3000 m, et la conception geotechnique est de plus en plus centree [s.sub.ur] les sediments mous des premiers 30 m du fond marin. En raison des difficultes et des couts eleves associes a la recuperation d'echantillons de qualite des sites profonds, les techniques in situ voient leur utilisation augmenter lors de la determination des parametres geotechniques de conception. Cet article resume les resultats obtenus lors d'un projet industriel conjoint, entrepris par l'Institut geotechnique norvegien et par le Centre for Offshore Foundation Systems a l'Universite de Western Australia, [s.sub.ur] l'utilisation de methodes in situ pour la caracterisation des sols marins mous et profonds. Le projet s'est penche [s.sub.ur] les etudes theoriques et empiriques de l'interpretation des donnees provenant d' essais au piezocone, au T-bar et au penetrometre a bille, reliant la resistance a la penetration aux resistances en cisaillement determinees par des essais scissometriques in situ et en laboratoire effectues [s.sub.ur] des echantillons de qualite elevee. Des directives pour interpreter les donnees d'essais in situ sont resumees, en particulier pour l'estimation de la resistance au cisaillement non drainee intacte et remaniee a partir des resistances a la penetration obtenues pour chaque type de penetrometre. Des suggestions sont aussi fournies pour le developpement futur des techniques d'essai in situ afin de maximiser le potentiel de la caracterisation in situ des sols mous et profonds. Mots-cles : etudes des sols marins, argile molle, penetration en ecoulement complet, resistance au cisaillement non drainee. [Traduit par la Redaction], Introduction Geotechnical properties of near-surface seabed sediments are of increasing importance for deepwater hydrocarbon field developments, where offshore installations will typically comprise wellheads and subsea completions, pipelines, and shallow anchoring [...]

A manually operated penetrometer (DMS) fitted with cylindrical (T-bar) and ball penetrometer tips was developed for measuring the profiles of undisturbed and remolded undrained shear strength within box-core samples. This paper summarizes the findings of a series of miniature penetrometer tests and vane shear tests that were carried out on reconstituted clay from a local site in Western Australia. The aim of the tests was to evaluate the potential of the DMS in characterizing the shear strength of seabed surficial sediments. It was found that the DMS gave essentially identical T-bar and ball penetration resistances but these were up to 17% lower than the net cone resistance. From the comparison between the T-bar and ball penetration resistance and the shear strengths measured from vane shear tests, average N factors of 11 and 14 were obtained for intact and fully remolded conditions, respectively. The test results suggest that the DMS is a reliable and efficient means of obtaining intact and remolded shear strength profiles. DOI: 10.1061/(ASCE)GT.1943-5606.0000379 CE Database subject headings: Clays; Penetration tests; Shear strength; Cyclic tests; Soft soils; Measurement. Author keywords: Clays; Penetrometers; Penetration resistance; Shear strength; Cyclic tests.

Seabed pipelines must be designed to accommodate thermal expansion--which is commonly achieved through controlled lateral buckling--and to resist damage from submarine slides. In both cases, the pipe moves laterally by a significant distance and the overall pipeline response is strongly influenced by the lateral pipe-soil resistance. Here, the process of pipe penetration and lateral displacement is investigated using a large-deformation finite element method, with a softening rate-dependent soil model being incorporated. The calculated soil flow mechanisms, pipe resistances, and trajectories agree well with plasticity solutions and centrifuge test data. It was found that the lateral resistance is strongly influenced by soil heave during penetration and the berm formed ahead of the pipe during lateral displacement. For 'light' pipes, the pipe rises to the soil surface and the soil failure mechanism involves sliding at the base of the berm. In contrast, 'heavy' pipes dive downwards and a deep shearing zone is mobilized, expanding with continuing lateral movement. The different responses are reconciled by defining an 'effective embedment' that includes the effect of the soil berm or wall ahead of the pipe. The relationship between normalized lateral resistance and effective embedment is well fitted using a power law. Key words: pipeline, clay, finite element method, buckling, penetration. Les tuyaux placees au fond de la mer doivent etre concjus de maniere a contenir l'expansion thermique--ce qui est normalement accompli par flambement lateral controle--et a resister aux dommages causes par les glissements sousmarins. Dans les deux cas, le tuyau se deeplace lateralement sur une distance significative, et le comportement global du tuyau est fortement influence par la resistance laterale entre le tuyau et le sol. Dans cet article, le processus de penetration du tuyau et de deeplacement lateral est evaluee a l'aide d'une meethode par elements finis pour les grands deplacements, a laquelle un modele de sol avec l'adoucissement des deformations dependant d'un taux est ajoute. Les mecanismes d'ecoulement, les resistances des tuyaux et les trajectoires calcules correspondent bien avec les solutions de la theorie de la plasticite et les donneees des essais a la centrifuge. Il a ete determine que la resistance laterale est fortement influencee par le soulevement du sol durant la penetration et aussi par la berme formeee au devant du tuyau durant le deplacement lateral. Dans le cas de tuyaux << leegers >>, le tuyau monte a la surface du sol et un glissement a la base de la berme est implique; dans le mecanisme de rupture du sol. A l'oppose, les tuyaux << lourds >> se deeplacent vers le bas et une zone de cisaillement profonde est mobiliseee et s'etend a mesure que le mouvement lateral s'avance. Ces comportements diffeerents sont combines dans le parametre << enfouissement effectif >> qui inclus l'effet de la berme ou du mur en avant du tuyau. La relation entre la re;sistance late;rale normalise;e et l'enfouissement effectif est bien repre;sente;e par une loi de puissance. Mots-cles: tuyau, argile, meethode d'eelements finis, flambement, penetration. [Traduit par la Redaction], Introduction Seabed pipelines are an increasingly significant component of offshore hydrocarbon developments. As exploration moves into deeper waters, more distant from shore, the design and construction of the seabed pipelines [...]

Pipelines are frequently subjected to active loading from slide events both on land and in the offshore environment. Whether the pipeline is initially buried or lying close to the surface, and whether it crosses the unstable region or lies in the path of debris originating from further away, the main principles are unchanged. The pipeline will be subjected to active loading over some defined length, related to the width of the slide, and as it deforms will be restrained by transverse and longitudinal resistance in adjacent passive zones. Ultimately the pipeline may come to a stable deformed shape where the continued active loading from the slide is equilibrated by the membrane tension in the pipeline in addition to the passive resistance. This problem has been explored by various writers and these principles are well established. However, to date no attempt has been made to develop a standard set of parametric solutions, which is the purpose of the current paper. Both analytical and numerical solutions of the problem have been developed, initially for slides acting normal to the pipeline but later extended to general conditions with the slide impacting the pipeline at some angle. It is shown that analytical solutions based on certain idealizations maintain their accuracy over a wide parameter range, and the net effect of the slide in terms of stresses induced in the pipe wall and maximum displacement of the pipeline may be captured in appropriate dimensionless groups. Design charts are presented for slide widths of up to 10,000 times the pipeline diameter for a practical range of other parameters such as the ratios of passive normal and frictional resistance to the active loading. Although the solutions are limited by some of the idealizations, they should provide a useful starting point in design, providing a framework for a more detailed numerical analysis for the particular governing conditions. DOI: 10.1061/(ASCE)GT.1943-5606.0000314 CE Database subject headings: Design; Underwater pipelines; Soil-pipe interactions; Landslides; Lateral loads. Author keywords: Pipeline design; Submarine pipelines; Soil-pipe interactions; Landslides; Lateral loads.

Three-dimensional large deformation finite-element (FE) analyses were performed to investigate plate anchor capacity during vertical pullout. The remeshing and interpolation technique with small strain approach was expanded from two-dimensional to threedimensional conditions and coupled with the FE software, ABAQUS. A modified recovery of equilibrium in patches technique was developed to map stresses after each remeshing. Continuous pullout of rectangular plate anchors was simulated and the large deformation results for strip, circular, and rectangular anchors were compared with model test data, small strain FE results, and plastic limit solutions. Interface conditions of no breakaway (bonded) and immediate breakaway (no tension) were considered at the anchor base. The effects of anchor roughness, aspect ratio, soil properties, and soil overburden pressure were investigated. It was found that the anchor roughness had minimal effect on anchor performance. For square and circular deep anchors under immediate breakaway conditions, the maximum uplift capacity increased with soil elastic modulus, which suggests that lower bound limit analysis and small strain FE analysis may overestimate the capacity. The soil beneath the anchor base separates from the anchor at a certain embedment depth near the mudline, once tensile stresses were generated. The ratio of separation depth to anchor width was found to increase linearly with the ratio of soil undrained shear strength to the product of soil effective unit weight and anchor width and was independent of the initial anchor embedment depth. DOI: 10.1061/(ASCE)GT. 1943-5606.0000210 CE Database subject headings: Plate anchor; Large deformation analysis; Finite element method; Capacities; Clays. Author keywords: Anchors; Soil deformation; Finite-element method; Clays; Three-dimensional analysis.

This paper presents results and analyses of the dynamic behavior of a small-diameter pile driven in very soft clay, with its tip embedded to a depth of 4.5 m with a clear distance of 1-1.5 m above a stiffer substratum. The research program included static and dynamic load tests performed over a period of 15 days, with blows from three different drop heights. The dynamic signals were analyzed using two different pile-soil interaction models. The performance of the dynamic models in predicting the shaft and base behavior of the model pile, as well as the change in bearing capacity and in some model parameters the dynamic with time, are addressed in particular. Key words: dynamic pile tests, soft clay, soil models, set up. Cet article presente les resultats et analyses du comportement dynamique d'un pieu de faible diametre enfonce dans de l'argile tres molle, avec sa point a une profondeur de 4,5 m et a une distance libre de 1 a 1,5 m au-dessus d'une fondation plus dure. Le programme de recherche comportait des essais de chargement statiques et dynamiques effectues sur une periode 15 jours, et consistaient de coups de trois elevations de chute differentes. Les signaux dynamiques ont ete analyses a l'aide de deux modeles differents d'interaction pieu-sol. L'article discute de facon particuliere de la performance des modeles dynamiques pour predire le comportement de l'arbre et de la base du pieu modelise, ainsi que de la dynamique dans le temps de la capacite portante et d'autres parametres du modele. Mots-cles : essais dynamiques de pieux, argile molle, modeles de sol, installation. [Traduit par la Redaction], Introduction Fine-grained soils exhibit time-dependent behavior, affecting their stress--strain response and shear strength. The most common processes are associated with water migration (consolidation), but other phenomena are also recognized, such [...]

Vertically installed plate anchors have been investigated in this paper by numerical analysis and centrifuge modeling. In the numerical analysis, the large deformation finite-element method (remeshing and interpolation technique with small strain) was used to simulate strip plate anchor rotation. In the centrifuge model tests, transparent soils were used to observe square anchor rotation. The loss in anchor embedment during anchor keying was assessed for anchors in uniform and normally consolidated soils with anchor pullout angle varying from 30[degrees] to 90[degrees] to the horizontal. It was found that the loss in anchor embedment during anchor keying may be expressed in terms of a nondimensional anchor geometry factor, which is a function of the eccentricity of the padeye, angle of loading, and the net moment applied to the anchor at the stage where the applied load balances the anchor weight. However, once the anchor geometry factor reaches a certain value, the loss in anchor embedment stabilizes at 0.25-0.5 times the anchor width. The loss in anchor embedment decreases linearly with decreasing pullout angle. Simple formulae and design procedures have been proposed to estimate the loss in anchor embedment during keying. DOI: 10.1061/(ASCE)GT.1943-5606.0000098 CE Database subject headings: Anchors; Clays; Centrifuge models; Deformation; Finite element method; Imaging techniques; Rotation.

Spudcan foundations for offshore mobile drilling rigs are large saucer-shaped foundations that can penetrate several tens of meters into soft sediments. The penetration depth is typically predicted by considering a wished-in-place foundation at different depths and following traditional bearing capacity approaches to assess the depth at which the estimated capacity matches the applied loading. However, the geometry of the spudcan and its progressive mode of penetration lead to soil failure mechanisms that differ markedly from those relevant to onshore practice. This paper presents a new rational design approach for assessing spudcan penetration in single layer clays based on a study combining centrifuge model testing and large deformation finite-element (FE) analysis. The design approach takes account of the evolving failure mechanisms in the soil, which start with cavity formation and surface heave at shallow penetration, gradually transforming to backflow of soil over the spudcan. A detailed FE parametric study has explored the relevant range of normalized strength, strength nonhomogeneity, and spudcan base roughness, with results validated against centrifuge model test data. The penetration response curves are presented in terms of profiles of bearing capacity factors, forming nondimensional design charts along with simplified expressions for convenient use in practice. Comparisons with approaches suggested in the SNAME design code suggest an urgent need to update current practice. DOI: 10.1061/(ASCE)GT.1943-5606.0000054 CE Database subject headings: Load bearing capacity; Centrifuge models; Clays; Finite element method; Heterogeneity; Foundation design.

The undrained remolded shear strength of soft clays is of importance in geosystem design, particularly for offshore structures. Common methods to estimate remolded shear strength, such as correlations with cone penetration data, direct measurement with an in situ field vane shear device, and laboratory measurements, produce varied results and can be particularly costly and time consuming. Full-flow penetrometers (T-bar and Ball) provide an alternative rapid method to estimate remolded shear strength and soil sensitivity through remolding soil by repeated cycling of the penetrometer up and down over a given depth interval. The cyclic penetration resistance degradation curve inherently contains information regarding remolded strength and sensitivity. The objective of this paper is to assess the ability of full-flow penetrometers to predict remolded strength and soil sensitivity, and to develop a suite of predictive correlations in which these properties can be estimated in the absence of complementary laboratory or in situ test data. To accomplish this, full-flow penetration profiles and cyclic tests were performed at five well characterized soft clay sites, which together represent the broad range of soils in which the penetrometers will be often used. A previously developed model for the reduction in penetration resistance with cycling is modified to predict the entire degradation curve, including the remolded penetration resistance using only measurements obtained during initial penetrometer penetration and extraction. Using field vane shear strength as the reference measurement, correlations are developed to predict soil sensitivity and remolded shear strength based solely on full-flow penetrometer data, which is particularly useful in site investigation programs where site specific data are not yet available or are sparse. Finally, the usefulness of these relationships is demonstrated by implementing them for two additional soft clay sites. DOI: 10.1061/(ASCE)GT.1943-5606.0000037 CE Database subject headings: In situ tests; Drainage soft soils; Clays; Sediments.