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The most commonly used procedure for prediction of the behaviour of laterally loaded piles is the P–y curve formulation, which gives a simple but efficient framework to predict the response of the pile. This framework is limited to a single direction of loading, while there are several situations in which a pile is subjected to lateral loads with varying direction, as for example in the case of wind or wave loads. Here an extended framework for P–y curve modelling is presented, in which several springs are considered around the pile perimeter at each depth. The advantage of this framework is that it remains as simple and practical as the original P–y curve method and does not need any further information or parameters. A procedure is proposed for the extension of a given unidirectional model to the corresponding multi-directional one. The effects of multi-directional loading are discussed based on the simulation results. With a change in loading direction, misalignment between load direction and total displacement occurs. In addition, this quite simple model enables deduction of the profile of irreversible soil displacements around the pile at various depths.

International audience; An offshore wind farm will be developed in France at the Fecamp site covering in excess of 67 km². In this location, medium to high density chalk containing flint nodules is found. In this paper, some of the hydro-mechanical properties of this specific marine chalk are presented, aiming to characterize the first meters of the chalk more precisely for the design of gravity base foundations. A series of un-drained static and cyclic triaxial tests carried out on 100 mm and 300 mm diameter specimens of weathered chalk are presented. Specimens have been recovered from 100 mm, 300 and 500 mm diameter vibrocore sections. Results show, upon undrained static tests, that the material presents essentially dilative behaviour and usually generates negative excess pore water pressures during shear. Upon undrained cyclic tests, the material shows a progressive development of fairly significant positive excess pore water pressures and relatively high values of axial strains. Results also indicate that the excess pore water pressure dissipation, after a sequence of cycles, induces a densification of the material which results, upon post-cyclic undrained static shear, in a more dilative response resulting in higher values of undrained shear strength.

International audience; Due to its heterogeneous nature and the presence of flint nodules, weathered chalk can be difficult to recover offshore in an intact state. On an offshore wind farm site comprising medium to high-density Chalk with flint, several sampling tools have been deployed including Geobor s rotary coring, push sampling, standard vibrocore of 100mm diameter and large diameter vibrocore of 300mm and 500mm diameter. Results of laboratory tests show the impact of the sampling, the sub-sampling and sample diameter on the behaviour of the tested chalk. If the drilling tends to partially remould the chalk, the vibro coring tends to density the chalk, this effect seems to be less pronounced with the increase of core diameter. The different states of densification are difficult to see on the density measurement but more visible on the dilative behaviour observed during the isotropic consolidated triaxial tests. The variation of permeability and the effect of cycles on the behaviour of the chalk are also discussed in the paper.

La plupart des éoliennes offshore sont fondées sur monopieux. L’augmentation constante de la capacité des turbines et l’insuffisance des procédures évoquées dans les documents normatifs, notamment en ce qui concerne la prise en compte des chargements cycliques, posent des défis pour leur dimensionnement. Dans le cas des sites français, la présence de sols et roches carbonatés, dont le comportement est encore mal connu aujourd’hui, rend la tâche encore plus complexe. Le projet SOLCYP+, lancé en 2017 pour une durée de 3 ans, doit permettre de disposer de nouvelles méthodologies fiables et robustes pour le dimensionnement des monopieux de grand diamètre y compris dans le contexte géotechnique du plateau continental français. Cet article présente une description détaillée du projet ANR SOLCYP+. On aborde, tout d’abord, le contexte, la problématique et les objectifs du projet puis, dans un second temps, on décrit plus en détail les quatre principales tâches scientifiques.

Abstract The first deep water geotechnical survey in South China Sea has been performed at Liwan 3–1 Field in Pearl River Mouth Bassin. The investigation comprised Piezocone Penetrometer Tests (PCPT), T-bar, insitu vane tests, pore pressure dissipation tests, jumbo piston cores, box cores, along with advanced laboratory testing. The in-situ and laboratory data results obtained have been used together with the geophysical data (AUV data) to provide the soil design parameters used for the design of the deepest PLEM and Manifold foundations (i.e. between 1300 and 1500m WD). The high quality and variety of in-situ and laboratory tests performed enable a sound comparison with other deep water sediments. Most of the soil properties of the Liwan 3–1 clays are in the range of those encountered in the Gulf of Guinea (Colliat et al. 2010). The use of scanning electron microscopy (SEM) revealed highly structured clay what is in accordance with the relatively high sensitivity of about 5 to 9 obtained from T-bar tests after 30 cycles. However some particularities arise in their mechanical behavior. The shear strength anisotropy (i.e. answer under different modes of shearing) is for example not significant. It can also be noted that the increase of shear strength with time or with the rate of shearing (i.e. respectively the thixotropy and rate effects) are less pronounced. Introduction Located about 300 kilometres southeast of Hong Kong, Liwan field is a major offshore gas discovery. The field contains contingent reserves of between 4 trillion and 6 trillion cubic feet of gas based on the Liwan 3-1-1 discovery well drilled in mid-2006 in Block 29/26. An AUV survey took place in 2009-2010 across five pipeline routes and two sites in the Liwan area. Some gravity cores were also taken at that time. An extensive geotechnical site investigation took then place in 2011 to investigate the deep water structure locations (Liwan 3–1 PLEM, manifolds and SDH), shallower locations (LH 29–1 manifold and SDA) and pipeline routes. This survey also included specific geohazard locations aiming at quantify the susceptibility of soil slope instability along the Liwan 3-1 to CEP pipeline route. The Liwan 3–1 field is located on the lower continental slope of the South China Sea (Figure 1a), in water depths comprised between 1300 and 1500m. Seabed gradients in the vicinity of the proposed seabed structures can be significant. The PLEM Location itself is located on a slope of 2.6°, on the east wall of a submarine canyon (Figure 1b). This large submarine canyon runs from north to south, crossing the LW 3–1 area, and is located between the West Manifold Location and the PLEM Location. A detailed engineering geolocical model together with a slope stability assessment and a debris flow model were developped along the canyon but will not be discussed in this paper. The present paper focuses on the deep water sediments encountered at the Liwan 3–1 structure locations. The soil investigation strategy, the soil physical and geotechnical properties are discussed and compared to the experience gained for deep water projects in the Gulf of Guinea and particularly to the state of the art paper presented at the ISFOG 2010 Conference in Perth (Colliat et al. 2010). The first Chinese deep water field offers many similitudes to other deepwater fields when looking at the shallow sediment properties. Some particularities were however highlighted by the laboratory test results. The impact of the observed differences on future foundation design and installation are discussed in the present paper.