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Many offshore geotechnical problems--such as cyclic T-bar penetration and lateral buckling of pipelines--are affected by the tendency of fine-grained soils to strain-soften due to remoulding. Careful calibration of the constitutive model parameters that control strain softening is essential for accurate simulation of these processes. This is usually achieved by matching constitutive model response with standard element test data, which implicitly assumes that homogeneous stress/strain fields exist within the sample. However, popular element test protocols (e.g., triaxial, simple shear) cannot apply sufficient deformation-- at least as measured at the boundaries--to achieve fully remoulded conditions. This work explores the potential to determine strain-softening parameters experimentally, directly from image-based full-field deformation measurements and external loading data. Artificial data generated from finite element simulations of biaxial compression and T-bar penetration tests, using a non-locally regularised strain-softening constitutive model based on Modified Cam Clay, are then used to demonstrate the potential of the proposed technique. The results demonstrate significant potential for the application of the technique to identify constitutive parameters from full-field measurements even when polluted with modest measurement noise. Key words: large deformation modelling, particle image velocimetry, full-field deformation measurement, constitutive parameter calibration, 1. Introduction Geotechnical problems--particularly in the field of offshore geomechanics----often involve significant remoulding of soil due to large movements of structural elements. Selected examples of such problems are cyclic T-bar [...]

The risk posed by seabed instability is of increasing significance as offshore activities including oil and gas developments continue to expand in this century. Many studies have considered runout of debris flows resulting from submarine landslides and potential impact on offshore infrastructure. However, initiation of slab failure resulting from shear band propagation (SBP) at the onset of a landslide has received less attention, although it is of key importance for estimating the scale and consequences of landslides. The present paper explores arrest of SBP as well as global slab failure above the shear band. The complete evolution of a submarine landslide from shear band initiation, propagation, slab failure, and arrest of SBP is observed through large-deformation finite element (LDFE) modelling. Governing equations for both dynamic and quasi-static SBP are established and solved, with results showing good agreement with the LDFE results. Lower limits for the final shear band length and for global slab failure are proposed for cases with high strain-rate dependency of shear strength, where shear band propagation is quasi-static; upper limits are proposed for cases without rate effects where the behaviour is dynamic. Key words: failure, landslides, shear strength, slopes, offshore engineering. Les risques poses par l'instabilite des fonds marins sont de plus en plus importants, car les activites d'exploitation de mer, y compris les developpements petroliers et gaziers, continuent de prendre de l'ampleur au cours de ce siecle. De nombreuses etudes ont pris en compte le debordement des coulees de debris resultant des glissements sous-marins et l'impact potentiel sur les infrastructures d'exploitation de mer. Cependant, l'initiation de la rupture de la plaque resultant de la propagation de la bande de cisaillement (PBC) au debut d'un glissement a recu moins d'attention, bien qu'elle soit d'une importance capitale pour estimer l'echelle et les consequences des glissements. Le present article explore l'arret de la PBC ainsi que la rupture de la plaque globale au-dessus de la bande de cisaillement. L'evolution complete d'un glissement sous-marin a partir de l'initiation de la bande de cisaillement, de la propagation, de la rupture de la plaque et de l'arret de la SBP est observee grace a une modelisation par elements finis de grandes deformations (<< LDFE >>). Les equations determinantes pour la PBC dynamiques et quasi statiques sont etablies et resolues, les resultats montrant un bon accord avec les resultats par LDFE. Des limites inferieures pour la longueur finale de la bande de cisaillement et pour la rupture globale de la plaque sont proposees pour les cas ou la vitesse de deformation depend fortement de la resistance au cisaillement, ou la propagation de la bande de cisaillement est quasi statique; des limites superieures sont proposees pour les cas sans effets de taux lorsque le comportement est dynamique. [Traduit par la Redaction] Mots-cles: echec, glissements, resistance au cisaillement, pentes, ingenierie d'exploitation de mer., Introduction Instability of submarine or subaqueous slopes is ubiquitous throughout the world, including much studied examples such as the giant Storegga landslide that occurred 8200 years ago in the North [...]

Current site investigation practice for offshore pipeline design relies on soil parameters gathered from boreholes or in situ test soundings to depths of 1-2 m below the mudline. At these depths, the fine-grained seabed is very soft and possesses low undrained strength, which can be difficult to measure. This paper describes a centrifuge test programme undertaken to evaluate the feasibility and performance of a novel penetrometer designed to assess the shallow strength of soft seabed over continuous horizontal profiles. This device is termed the vertically oriented penetrometer (VOP). Tests were performed on a normally consolidated kaolin sample, with the VOP translated horizontally at velocities ranging from 1 to 30 mm/s, after embedding the VOP at 30 and 45 mm depths. All tests involved many cycles of VOP forward and backward movement to assess its potential to derive the ratio of intact to fully remoulded strength. Strength determination is achieved by dragging the VOP at a specified embedment depth along the soil surface, and deriving the soil strength from the measured resistance as if the VOP were a laterally loaded pile. The VOP is shown to yield comparable strength measurements to that of a T-bar penetrometer. The VOP is a potentially valuable addition to the range of tools used to characterize soil strength, both in small-scale centrifuge models and, following practical development, potentially also in the field. Key words: clays, penetrometer, pipeline, shear strength, site investigation. Pour concevoir des pipelines en mer, on se base habituellement sur les parametres du sol mesures dans les trous de forage ou lors de sondages d'essai sur le terrain realises a des profondeurs comprises entre 1 et 2 m sous le fond marin. A ces profondeurs, le sol finement granuleux est tres mou et presente une faible resistance non drainee, qui peut etre difficile a mesurer. Le present article decrit un programme d'essais en centrifugeuse visant a evaluer la faisabilite et les performances d'un nouveau type de penetrometre permettant d'estimer la resistance superficielle d'un fond marin mou sur des profils horizontaux continus. Cet appareil est appele penetrometre oriente verticalement (POV). Les essais ont ete effectues sur un echantillon de kaolin normalement consolide, le POV etant soumis a une translation a des vitesses variant entre 1 et 30 mm/s, apres enfouissement du POV a des profondeurs de 30 et 45 mm. Tous les essais ont consiste en nombreux cycles de mouvements du POV en avant et en arriere, afin que l'on puisse evaluer sa capacite a mesurer le quotient de la resistance au cisaillement a l'etat intact par la resistance au cisaillement a l'etat totalement remanie. On a pu determiner la resistance en tramant le POV a une profondeur d'enfouissement specifique le long de la surface du sol et en deduisant la resistance du sol a partir de la resistance mesuree, comme si le POV etait un pieu charge lateralement. On constate que le POV fournit des mesures de resistance comparables a celles obtenues a l'aide d'un penetrometre a barre en T. Le POV est donc tres utile et pourrait s'ajouter a l'eventail des outils servant a caracteriser la resistance du sol dans le cadre d'essais en centrifugeuse sur des modeles reduits et possiblement sur le terrain apres une phase de developpement pratique. [Traduit par la Redaction] Mots-cles: argiles, penetrometre, pipeline, resistance au cisaillement, etude sur le terrain., Introduction This paper describes the development of a novel device for measuring the near-surface soil undrained strength, named the vertically oriented penetrometer (VOP). This device is a short rigid cylinder, [...]

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.

This paper presents a numerical investigation of the effect of foundation size on the response of shallow circular foundations on siliceous and calcareous sands. The study is based on the predictive capabilities of the MIT-S1 soil model for simulating both the compression and shear behaviors of natural sands over a wide range of densities, [K.sub.0] values and confining pressures. The paper highlights the variations in the deformation mechanisms for the siliceous and calcareous sands cases. The assessment of the bearing capacity factor, [N.sub.[gamma]], is examined, showing a dramatic decrease in the values with increasing foundation size for the case of footings on calcareous sands, eventually converging to a terminal [N.sub.[gamma]] value. At this stage the sand resistance is insensitive to variations in initial density and foundation size because the sand tends to loose its initial characteristics due to grain crushing, leading the material rapidly toward ultimate conditions. In the silicious sand case, it is found that, eventually, for extremely large footing diameters, the deformation mechanism progresses toward a punching shear mechanism, rather than the classical rapture pattern accompanied by surface heave as employed in current bearing capacity equations. A dimensional transition between the failure mechanisms can clearly be defined, referred to as a 'critical size' in the [N.sub.[gamma]]-D relationship. CE Database subject headings: Sand; Calcareous soils; Silica; Shallow foundations; Size effect; Finite element method; Numerical analysis.

A CPT-based method is presented for estimating the self-weight penetration and suction required during the installation of suction caissons in medium dense to dense sand. Existing methods, although fundamental in nature, suffer from the difficulty in estimating key input parameters such as an appropriate bearing factor for the tip resistance and frictional coefficients for skirt friction. Instead, the proposed method is based directly on the cone resistance profile, starting with the Det norske Veritas approach for calculating the installation resistance of skirted foundations. The approach is modified to include a simple linear reduction in end beating on the skirt tips and internal friction with the level of suction, with those components of resistance assumed to reduce to zero once the suction reaches the critical level corresponding to hydraulic failure of the soil plug. The method is coupled with a seepage model so that, for a given pumping rate, the penetration and corresponding resistance can both be expressed as a function of time. Results of calculations with this complete model are shown to compare well with data from centrifuge model tests and with published data from suction caisson installations. CE Database subject headings: Suction; Caissons; Sand; Cone penetration; Installation; Pumps; Centrifuge models.

This paper discusses the development of a framework for classifying soil using normalized piezocone test (CPTU) data from the corrected tip resistance ([q.sub.t]) and penetration pore-water pressure at the shoulder ([u.sub.2]). Parametric studies for normalized cone tip resistance (Q = [q.sub.cnet]/[[sigma]'.sub.v0]) and normalized excess pressures ([DELTA][u.sub.2]/[[sigma]'.sub.v0]) as a function of overconsolidation ratio (OCR=[[sigma]'.sub.vy]/[[sigma]'.sub.v0]) during undrained penetration are combined with piezocone data from clay sites, as well as results from relatively uniform thick deposits of sands, silts, and varietal clays from around the globe. The study focuses on separating the influence of yield stress ratio from that of partial consolidation on normalized CPTU parameters, which both tend to increase Q and decrease the pore pressure parameter ([B.sub.q] = [DELTA][u.sub.2]/[q.sub.cnet]). The resulting recommended classification chart is significantly different from existing charts, and implies that assessment of data in Q-[DELTA][u.sub.2]/[[sigma]'.sub.v0] space is superior to Q-[B.sub.q] space when evaluating piezocone data for a range of soil types. Still, there are zones of overlap for silty soils and heavily overconsolidated clays, thus requiring that supplementary information to Q and [DELTA][u.sub.2]/[[sigma]'.sub.v0] be obtained in unfamiliar geologies, including variable rate penetration tests, dissipation tests, CPT friction ratio, or soil sampling. CE Database subject headings: Soil classification; Cone penetration tests; Silts; Sand; Clays; Overconsolidated soils.

The behavior of strip and circular plate anchors during vertical pullout in uniform and normally consolidated clays was studied in this paper by means of small strain and large deformation finite-element analyses. Both fully bonded (attached), and 'vented' (no suction on rear face), anchors were considered. The current numerical results were compared with existing laboratory test data, finite-element results, and analytical solutions. This study showed that, in small strain analysis, the scatter of existing data was mainly due to the effect of soil stiffness. In large deformation analysis, when soil and anchor base were attached with suction, the pullout capacity factor formed a unique curve independent of the soil strength ([s.sub.u]), soil effective unit weight ([gamma]') and anchor size (B=width of strip anchor and D=diameter of circular anchor). The transitional embedment depth ratio, [H.sub.SD]/B or [H.sub.SD]/D, (where [H.sub.SD]=transition depth between shallow and deep embedment) was 1.4 for a strip anchor and 0.75 for a circular anchor. The ultimate pullout capacity factors ([N.sub.c]) for deep embedment were 11.6 and 11.7 for smooth and rough strip anchors and 13.1 and 13.7 for smooth and rough circular anchors, respectively. However, when the anchor base was vented, the soil stayed attached to the anchor base for deep embedment, and the pullout capacity was therefore the same as for the attached anchor. The separation depth ratio, [H.sub.S]/B or [H.sub.S]/D, (where [H.sub.s]=embedment depth at which the soil and anchor base separated) was found to increase linearly with the normalized strength ratio, [s.sub.u]/[gamma]' B or [s.sub.u]/[gamma]'D. CE Database subject headings: Anchors; Pull out resistance; Soil strength; Deep water; Finite element method; Deformation.

The study is on the electrokinetic strengthening of caisson anchors embedded in offshore calcareous sand. The effects of electrode configuration on the effectiveness of electrokinetic treatment are investigated based on electric field analysis and are verified by results from a series of large scale laboratory tests on caisson models of 200 mm diam and 400 mm height, embedded in calcareous sand submerged under seawater. The electrokinetic treatment generates cementation of soil solids as well as bonding between soil and caisson shafts, which leads to increases in the side resistance and overall pullout resistance. The effectiveness of electrokinetic treatment is directly related to the electric field intensity. A linear relationship is observed between the increase in the side resistance and energy consumption. The study shows that the effectiveness of electrokinetic treatments can be maximized by the optimization of the electric field distribution through the electrode configuration. DOI: 10.1061/(ASCE)1090-0241(2008)134:3(352) CE Database subject headings: Soil stabilization; Caissons; Anchors; Cements; Soil-structure interaction; Pull-out resistance.

Suction caissons are increasingly being used for offshore anchors because of their ease of installation. However, for soil profiles that have sand overlain by layers of silt, there are reasons to believe that it may not be possible to install suction caissons. This may happen because the low permeability of the silt will create a hydraulic blockage, and thus diminish the upward hydraulic gradient required to reduce the penetration resistance in the sand to enable caisson penetration. The tendency of the silt to be sucked up, and its effect on the underlying sand, are not clearly understood. Furthermore, the blockage by the silt layer may be less than if a clay layer is present. This is because scouring of the silt may occur, allowing an upward seepage gradient to develop, and hence causing a reduction in penetration resistance. A series of suction caisson installation tests have been conducted in a geotechnical centrifuge to provide data on the penetration resistance and mechanisms for soil profiles where silt layers are present, either on top, or interbedded between layers of sand. In these tests, the thickness of the silt layer and its depth below the sand surface have also been varied. It has been found that if silt overlies the sand, a larger suction force is required for installation than when installation occurs in homogeneous sand, but that this force is still much smaller than the soil resistance when the caisson is pushed into the ground. When a silt layer is present, the suction pressures are observed to follow a similar trend that is independent of the position and thickness of the silt layer. Scouring of silt was evident in the tests, and significant upward movement of the soil plug inside the caisson was observed in all soil profiles when silt layers were present. The plug height was seen to reduce after the suction was turned off, suggesting that the resulting heave was unstable. DOI: 10.1061/(ASCE)1090-0241(2007)133:10(1183) CE Database subject headings: Suction; Caissons; Installation; Offshore structures; Layered soils; Sand; Silts.

Abstract: Large deformation finite element (LDFE) analyses were performed to study the installation of caissons by suction and jacking in normally consolidated clay. The penetration of the caisson wall was [...]

Background: Meniscal tears in the avascular zones do not heal. Although tissue-engineering approaches using cells seeded onto scaffolds could expand the indication for meniscal repair, harvesting autologous cells could cause [...]

This paper discusses the effects of penetration rate on the penetration resistance in soft clay for various shaped penetrometers (cone, T-bar, ball, and plate) and for T-bars with different aspect ratios. Constant rate ('normal') and variable rate ('twitch') penetration tests, where the penetration rate was successively halved over eight steps with the penetrometer advanced by one or two diameters in each step, were undertaken in the beam centrifuge at the University of Western Australia. The tests were conducted on samples reconstituted from clay collected from the Burswood site in Western Australia. The twitch tests showed higher penetration resistance than the corresponding normal tests after the penetration rate had been reduced by a factor of 16 due to cumulative effects of partial consolidation. The penetration rate at which the resistance started to increase due to partial consolidation was used to estimate the consolidation coefficient, [c.sub.v], of the reconstituted clay. The interpreted [c.sub.v] values were similar to values estimated from other consolidation data, both in the centrifuge and from laboratory Rowe cell and constant rate of strain consolidation tests. In addition, results from in situ twitch tests at the Burswood site were examined to evaluate viscous effects on the penetration resistance. DOI: 10.1061/(ASCE)1090-0241(2006)132:9(1188) CE Database subject headings: Centrifuge model; Clays; Loading rate; Penetration resistance; Penetration tests; Viscosity.

Ref.: Can. Geotech. J. 52(6): 682-693 (2015) dx.doi.org/10.1139/cgj-2014-0120. On page 689, right column, eighth line of the second paragraph, replace 'Mmax/B2Lsu = 4.17' with '[M.sub.max]/[B2Ls.sub.u] = 2.05'. Received 20 July [...]

There is little information in the geotechnical literature regarding the influence of the type of cement on the engineering behavior of cemented soils. This paper explores the mechanical behavior of a calcareous soil under triaxial loading after treatment with different types of cement, namely Portland cement, gypsum, and calcite. To identify the specific effects of each cement type a parametric study was undertaken, where factors such as density and unconfined compressive strength were maintained constant for each cementing agent. Samples of the cemented soil were examined under optical and electron microscopy to understand the bond mechanism created by each cement. Results from triaxial testing have shown that, despite having the same unconfined compressive strength and density, the effective stress paths and postyield response are significantly different, mainly because of the different volumetric response upon shearing. Samples prepared using Portland cement showed ductile yield and strong dilation afterwards; calcite and gypsum-cemented samples exhibited brittle yield, generally followed by contractive behavior. The paper discusses the results and explains the reasons behind the differences in the mechanical response. DOI: 10.1061/(ASCE) 1090-0241(2002) 128:6(520) CE Database keywords: Calcareous soils; Portland cements; Contraction; Triaxial tests; Gypsum.

The results of centrifuge modeling of pipe-soil interaction for shallowly embedded offshore pipelines are presented. A non-associated bounding surface model is constructed in vertical-horizontal (V-H) load space on the basis of test data and the theory of plasticity to simulate the response of a pipeline embedded in sandy soil under combined (vertical and horizontal) monotonic loading, taking into account possible pre-loading effects. The model needs nine parameters that can be back calculated from model or field tests and in some cases estimated theoretically. It provides a suitable basis for modeling the load-displacement response of shallowly embedded offshore pipelines. The model reproduces the key features of the load-displacement response of pipelines observed in centrifuge model tests. In particular, the adoption of bounding surface plasticity allows a gradual transition from elastic to plastic response to be simulated and the introduction of a non-associated flow rule allows the model to predict the strain-softening behavior of pipes under horizontal loading. The lateral breakout resistance predicted by the model agrees very well with experimental data. CE Database keywords: Offshore pipelines; Calcareous sand; Bounding surface; Models; Plasticity.

Finite element analysis of dynamic foundation problems requires the use of transmitting boundaries to model the radiation of waves from the finite element mesh into the far field. Problems involving inelastic behavior of the soil in the near field are most readily solved in the time domain. The standard viscous boundary is widely used in such situations. However, in axisymmetric situations this boundary is inappropriate. This paper develops plane strain boundary equations for axisymmetric shear and dilation waves based on an approximation of the form of the outward traveling waves. These boundary equations are shown to be equivalent to mechanical systems with frequency independent components. The complex stiffnesses of the new boundaries are compared with the equivalent viscous and plane strain boundary stiffnesses, and the new boundaries are found to agree closely with the plane strain boundaries. The response of an extended axisymmetric finite element mesh subjected to a transient force of the type generated by pile hammers is computed and compared to the responses of the same mesh truncated with various transmitting boundaries.

In most soil types, it is generally assumed that the shaft capacity of a pile is identical under both tensile and compressive loading. However, there is widespread experimental evidence that in sand the shaft capacity is significantly lower for tensile loading, or uplift, than for compressive loading. This paper describes the results of a parametric study that was conducted to explore the theoretical basis for such differences. It is shown that the primary cause of lower tensile capacity is due to a Poisson's ratio effect, and that the ratio of tensile to compressive shaft capacity may be expressed as a function of the relative compressibility of the pile and the slenderness ratio. Design recommendations are proposed, and corroborated with results from high-quality field tests.

The piled raft is a geotechnical composite construction, consisting of the three elements piles, raft, and soil, which is applied for the foundation of tall buildings in an increasing number. In a parametric study, 259 different piled raft configurations have been analyzed by means of three-dimensional elastoplastic finite element analyses. In the study, the pile positions, the pile number, the pile length, and the raft-soil stiffness ratio as well as the load distribution on the raft has been varied. In the scope of this paper, the results of the parametric study are presented and design strategies for an optimized design of piled rafts subjected to nonuniform vertical loading are discussed. DOI: 10.1061/(ASCE)1090-0241(2004)130:1(1) CE Database subject headings: Foundation design; Pile foundations; Raft foundations; Vertical loads; Numerical analysis; Finite element method; Differential settlement, Bending moments.