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The ball penetrometer is a full-flow penetrometer used as an alternative to the traditional cone penetrometer for characterizing the strength of soft sediments, particularly for offshore engineering, due to its large projection area. However, if the ball is penetrated under partially drained conditions, the resistance of the ball changes with the penetration velocity. The performance of ball penetration is examined employing a coupled large-deformation finite-element method. The reliability of numerical simulations under undrained and partially drained penetrations is verified by comparing with previous tests in the chamber and centrifuge. The backbone curve determining the penetration resistance on the spherical probe is proposed to quantify the influence of partially drained conditions, which captures the effect of the ratio of the diameters of the shaft and ball. Base on the backbone curve derived, an interpretation approach is proposed to predict the effective internal friction angle using the net resistance measured in the ball penetration tests with different penetration velocities. [ABSTRACT FROM AUTHOR]

Skirted mudmats are commonly used to support offshore infrastructure. However, these may not be able to provide sufficient capacity to notably withstand the lateral loads applied by jumpers and connectors. The concept of hybrid foundation system was therefore proposed to enhance the capacity in a targeted fashion, through addition of internal suction caisson compartments. This paper presents a numerical investigation into the undrained bearing capacity of a rectangular-shaped hybrid foundation with two caisson units. Uniaxial capacities under vertical, horizontal, and moment loading are reported, but the focus lies on the horizontal-moment planes due to the anticipated low vertical load on the foundation. Detailed discussion highlights the contribution of the internal caisson compartments to the significant increases in horizontal capacity compared to a simple rectangular skirted mat through changes in the failure mechanism. This results not only in changes in size, but also in shape, of the capacity envelope. The study was extended to more general horizontal-moment loading conditions, where the shape of the capacity envelope was found to remain approximately constant. This applies to the hybrid foundation and the rectangular skirted mat in the homogeneous soil considered here. An expression is proposed that provides a slightly conservative approximation of the capacity envelope under combined horizontal and moment loading from any direction. Key words: hybrid foundation, skirted foundation, subsea, offshore foundation, combined loading, capacity. Les patins juponnes sont couramment utilises pour supporter les infrastructures en mer. Cependant, ceux-ci pourraient ne pas etre capables de fournir une capacite suffisante pour supporter les charges laterales appliquees par les bretelles et les connecteurs. Le concept de systeme de fondation hybride a ainsi ete propose pour ameliorer la capacite d'une maniere ciblee, par l'ajout de compartiments internes dans les caissons de succion. Cet article presente une investigation numerique de la capacite portante non drainee d'une fondation hybride de forme rectangulaire ayant deux unites de caisson. Les capacites uniaxiales obtenues en chargement vertical, horizontal et en moment sont rapportees, mais l'emphase est mise sur les plans horizontaux-moments causes par la faible charge verticale anticipee sur la fondation. Une discussion detaillee souligne la contribution des compartiments du caisson interne a l'augmentation significative de la capacite horizontale comparativement aun simple patinjuponne rectangulaire. Cette augmentation est due a des changements dumecanisme de rupture. Ces resultats varient l'enveloppe de capacite non seulement par sa taille, mais aussi par sa forme. L'etude a ete etendue a des conditions de chargement moment-horizontal plus generales, dans lesquelles la forme de l'enveloppe de capacite s'est averee demeurer approximativement constante. Ceci s'applique a la fondation hybride et au patinjuponne rectangulaire dans le sol homogene considere dans cette etude. Une expression est proposee afin d'offrir une approximation legerement conservatrice de l'enveloppe de capacite sous chargement horizontal et de moment combines, de n'importe quelle direction. [Traduit par la Redaction] Mots-cles: fondation hybride, fondation juponnee, sous la mer, fondation en mer, chargement combine, capacite., Introduction Offshore shallow foundations, usually referred to as mudmats, are widely used to support on-bottom structures such as well manifolds, pipelines end terminations (PLETs), and in-line structures. Mudmats are usually [...]

Monopiles are popular solutions as the foundation to support offshore wind turbines (OWTs), which suffer from various amplitudes of continuous lateral cyclic wind and wave loading. The accumulation of tilt and change of the natural frequency of OWTs under cyclic loading have become crucial issues for OWT design. Hence the monopile-tower-soil system was established at the small-scale level based on similarity laws with a suit of constant-amplitude and multi-amplitude tests in dense sand. Two sets of gear-driving assembly were successfully set up to achieve the application of cyclic loading to the model OWT. The amplitude and symmetry of cyclic loading were specified as three indicative regions according to those of real wind farms. On the basis of test results, the two-way loading was found to be the most hazardous situation and the preloading condition led to a high accumulation of tilt. The change of natural frequency was controlled by the load magnitude and tended to increase during cyclic loads, while a sharp decrease was observed when sand subsidence was generated. The post-cyclic lateral capacity seemed to be a slight increase compared with the static capacity. The relevant analyses based on test results can provide practical recommendations for OWT design. [ABSTRACT FROM AUTHOR]

Bucket foundation is a promising solution to support offshore wind turbines, due to rapid and quiet installation, low fabrication cost, etc. However, when the foundation is of considerable size (i.e., large diameter with low depth) and is in soft marine sediments, the reliability of the bucket foundation may be low. The large peripheral skirt of a bucket foundation may not confine the internal soil well enough to resist complex environmental loads, leading to a low utilization ratio. This study describes a type of stiffened bucket foundation that employs an internal cruciform skirt, which is an optimization of the conventional bucket foundation. The undrained capacity performance under general loading was systematically investigated by means of a three-dimensional finite element analysis, with the effects of foundation depth and soil strength heterogeneity considered. Parallel comparative analyses for both conventional and solid bucket foundations were also implemented. By comparing both uniaxial and combined loading capacities, the difference in bearing performance was examined and interpreted, and the advantage of employing an internal cruciform skirt and its suitable site conditions was highlighted. Furthermore, a suite of formulae is provided to guide the practical design of the bucket foundation with internal cruciform skirt. [ABSTRACT FROM AUTHOR]

Biogrouting, which is a new method for soil improvement, was used in an attempt to cement a type of hydraulic fill fine sands (called black sands) in reclamation projects in Tianjin, China, to form a working layer for mechanical equipment. Several factors influencing biogrouting with regard to cementing solution, including injection frequency, reaction time, concentration, and flow rate, were controlled to prepare black sand columns. This paper reports on an investigation of bacterial fixation, calcium ion utilization, and calcium carbonate distributions of biogrouted sand specimens. At the end of the tests, the geotechnical performances of the sand specimens were determined. The results showed that the biogrouting method effectively solidified black sands, by increasing the unconfined compressive strength of a sand column to 1.91 MPa and reducing the permeability coefficient by three orders of magnitude. A relationship between the unconfined compressive strengths and calcium carbonate contents was put forward, in addition to a relationship between the permeability coefficients and the calcium carbonate contents. According to the experimental results, some reasonable suggestions regarding the application of biogrouting to the consolidation of hydraulic fill fine sands in reclamation projects were proposed. [ABSTRACT FROM AUTHOR]