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The traditional foundation design does not consider the bearing capacity under multi-directional coupling load. However, the foundation is usually subjected to vertical (V), horizontal (H) and moment (M) loading simultaneously on the seabed. The present study examines the undrained multi-directional bearing capacity of hybrid subsea foundation in saturated soft clay using finite element analysis. The contribution of the mudmat and the suction bucket to the bearing capacity of the hybrid subsea foundation was evaluated. The results show that the suction bucket can effectively make up for the lack of horizontal anti-slip and anti-overturning ability of the mudmat. It has a significant contribution to the horizontal and moment bearing capacity. In addition, the failure envelope of bearing capacity in horizontal-moment (H-M), vertical-horizontal (V-H), and vertical-moment (V-M) load space is obtained by using prescribed displacement ratio loading method. Based on the simulation results, the expression of approximate envelope of foundation bearing capacity under combined load of horizontal and moment is proposed. The study also found that a certain value of vertical load can increase the horizontal and moment bearing capacity of the hybrid subsea foundation, while excessive vertical load will lead to a decrease in bearing capacity. [ABSTRACT FROM AUTHOR]

Helical piles are being increasingly considered for offshore applications as they avoid the acoustic emissions associated with pile driving, and they provide additional capacity relative to a driven pile. In this paper, the installation and tensile capacity of helical piles is considered through a combination of centrifuge experiments and large-deformation finite-element analyses within a coupled Eulerian–Lagrangian framework. The experiments provide a basis for validating the numerical simulations, but also quantify the expected installation torque and undrained tensile capacity, including the variation with time after installation. The numerical simulations extend the parameter space investigated experimentally, considering the number of helices, their spacing and pitch, in addition to the ratio of pile shaft to helix diameter and the profile of undrained shear strength. Mechanisms revealed through the numerical simulations are reflected in a new analytical model for calculating undrained tensile capacity, which is seen to agree reasonably well with the numerically and experimentally determined capacities. [ABSTRACT FROM AUTHOR]

Circular open caissons are deep foundations sunk into the ground utilising the self-weight of cutting edge and steining as driving force along with the subsequent failure of soil in bearing. During the sinking of the caisson, the clay in contact with the cutting edge is subjected to undrained loading and the controlled sinking of the caisson can be achieved by evaluating the undrained bearing capacity of the cutting edge. In the study, the undrained bearing capacity factor (N) of the cutting edge for varying cutting angle (b), radius ratio of the caisson (ri/ro), full embedment of the caisson (d), removal of soil within the caisson (d'), and different roughness (α) conditions of the steining are evaluated using finite element limit analysis (FELA). The factors affecting the undrained stability of caisson considering all practical scenarios are addressed and presented as charts to be used in practice. [ABSTRACT FROM AUTHOR]

The design of an offshore wind turbine system varies with the turbine capacity, water depth, and environmental loads. The natural frequency of the structure, considering foundation flexibility, forms an important factor in structural design, lifetime performance estimates, and cost estimates. Although nonlinear numerical analysis in the time domain is widely used in the offshore industry for detailed design, it becomes necessary for project planners to estimate the natural frequency at an earlier stage and rapidly within reasonable accuracy. This paper presents a compendium of mathematical expressions to compute the natural frequencies of offshore wind turbine (OWT) structures on various foundation types by assimilating analytical solutions for each type of OWT, obtained by a range of authors over the past decade. The calculations presented can be easily made using spreadsheets. Example calculations are also presented where the compiled solutions are compared against publicly available sources. [ABSTRACT FROM AUTHOR]

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

In order to satisfy the exceptional conditions imposed by the offshore structures, a particular attention should be paid to the stability of shallow foundations resting on purely cohesive soil. One important specification of the offshore foundations is their soil-footing interface which can sustain tension. This paper studies the effect of the tensile strength of this interface on the undrained bearing capacity of a strip footing and assesses the reliability of the effective width method under eccentric loading. This is done by a numerical modelling using the finite difference method. Failure envelopes, failure mechanisms and normal stress distribution at the interface are presented and compared with available results from literature. The results show that the effective width method is not reliable in the presence of the tensile strength at the interface. This strength yields supplementary stability and keeps the footing in contact with the soil even under low vertical loading. [ABSTRACT FROM AUTHOR]

The dynamic stability of offshore foundations in the marine environment is one of the major technical challenges. Millions of loading cycles from waves and winds act on the foundations and seabed in their entire service life. The mixing of adjacent soil layers due to naturally occurring sediment or the construction process raises more difficulties in the design. Previous studies have focused on the dynamic constitutive relations of idealized clean sand or clay under cyclic loading, while the cyclic characteristics of sand-clay mixtures are still unclear. In this study, the dynamic responses of sand-clay mixtures under a large number of shear cycles were investigated through 25 constant-volume cyclic direct simple shear tests on sand-clay mixtures with sand contents of 0 %, 25 %, 50 %, and 75 %. The results indicate that high sand contents and high cyclic stress ratios accelerate the reduction of effective stress in sand-clay mixtures, resulting in a more rapid increase in shear strain. As the sand content increases from 0 % to 75 %, the normalized shear modulus decreases by 35.9 % at a shear strain of 1 %. In contrast, the normalized dynamic shear strength is reduced from between 0.490 and 0.525 to between 0.181 and 0.325 after over 5000 loading cycles. • Higher sand content makes stress paths reach the CSL earlier and hysteresis loops dumpier. • Sand content increases the accumulation of plastic strain with increasing shear cycles. • Sand content accelerates the reduction of the cyclic shear modulus of sand-clay mixtures. • Sand content increases the damping ratio of sand-clay mixtures under cyclic shearing. • Sand content reduces the long-term cyclic shear strength of the sand-clay mixtures. [ABSTRACT FROM AUTHOR]

Structural health monitoring for offshore wind turbine foundations is paramount to the further development of offshore fixed wind farms. At present time there are a limited number of foundation designs, the jacket type being the preferred one in large water depths. In this work, a jacket-type foundation damage diagnosis strategy is stated. Normally, most or all the available data are of regular operation, thus methods that focus on the data leading to failures end up using only a small subset of the available data. Furthermore, when there is no historical precedent of a type of fault, those methods cannot be used. In addition, offshore wind turbines work under a wide variety of environmental conditions and regions of operation involving unknown input excitation given by the wind and waves. Taking into account the aforementioned difficulties, the stated strategy in this work is based on an autoencoder neural network model and its contribution is two-fold: (i) the proposed strategy is based only on healthy data, and (ii) it works under different operating and environmental conditions based only on the output vibration data gathered by accelerometer sensors. The proposed strategy has been tested through experimental laboratory tests on a scaled model.

Plate anchors are of vital importance for both onshore and offshore facilities. The current study has been focused on the pullout capacity factors of rectangular anchors with wide range of aspect ratios under coupling effects of embedment ratios, anchor inclinations, overburden pressure and non-homogeneity of the clay. Three-dimensional small strain finite element (FE) analyses based on ABAQUS are carried out. After verifying the current model with the existing numerical solutions, the FE results are obtained, and relative comprehensive formulas have been proposed to evaluate the pullout capacity factor with the given parameters. The anchor with aspect ratio less than one has outlier performance in normally consolidated (NC) clay, which has also been discussed based on the soil flow mechanism. [ABSTRACT FROM AUTHOR]

Global warming is becoming worse owing to carbon dioxide emissions around the world, and eco-friendly energy for reducing carbon dioxide emissions is gaining importance. Wind power plants are the most representative of the environmentally friendly energy power plants built in the ocean. The fatigue loading and long-term dynamic behavior of offshore soils are important considerations in the construction of structures such as wind turbines in the ocean as they are subject to long-term loads such as wind and wave loads. A design graph presents the short- and long-term behaviors of soil. Several laboratory tests are typically conducted to create design graphs. In this study, a cyclic simple shear test conducted at various confining pressures and relative densities is presented in design graphs. The authors analyzed the sensitivity of the relative density and the confining pressure, and proposed a drawing technique to easily create two-dimensional design graphs. The authors found that the effect of the relative density on the design failure curve was higher compared with that of the confining pressure. The elliptic equation graph achieved the best match to the design failure curve, and the design failure curve drawing technique was summarized in five stages. In addition, the normalized cyclic stress ratio graph to distinguish safety or failure was presented.

Results of finite-element analyses calculating the undrained capacities of skirted circular foundations under uniaxial vertical, horizontal, and moment loading are presented. Parallel finite-element analyses using both the Tresca failure criterion and the modified cam clay (MCC) model are reported. The variations in capacity are presented as functions of embedment and soil-strength heterogeneity as a series of graphs. Closed-form formulas of uniaxial capacities are also provided. To account for the complexity in the results, a novel method of separating the contributions of soil above and beneath the skirt tip and for the constant and linearly varying components of the undrained shear-strength profile is outlined. This method can be used to estimate the undrained ultimate uniaxial capacity factors of skirted circular foundations in clay for any given embedment ratio and strength heterogeneity. Its versatility is also shown through validation against previously published embedded strip footing data. The results provide both equations for engineers to use in design and a database that can be used in future research to calculate and express the consolidated undrained capacity under combined loading. [ABSTRACT FROM AUTHOR]

Suction buckets acting as supports for jacket structures may constitute a viable foundation solution for offshore wind turbines. While monopiles dominate the industry, suction buckets remain uncommon despite their advantages in transitional water depths. One of the reasons stems from challenges of achieving optimal design due to scarce experience and knowledge, as the mechanisms governing foundation response to different drainage conditions are poorly understood. This paper contributes with new insights into tensile behavior of suction buckets based on experimental evidence. A defining property of bucket foundations is the ability to withstand extreme uplift forces on account of suction, which represents the core subject of this study. All tests involved a medium-scale model installed in sand in a pressurized environment. A novel feature of this research consists of examining the relative importance of soil density. By varying the relative density (40–90%) and the uplift rate (0.05–500 mm/s), a full range of drainage and soil conditions was explored. Suction pressure generated during partially drained or fully undrained uplift tends to reach similar values regardless of initial relative density. This key finding demonstrates how the soil state is altered due to jacking installation and cyclic pre-shearing. Regression models are established to capture the dependency of tensile capacity and initial stiffness on uplift rate. • Relative density of sand has insignificant effects on tensile response of suction buckets. • Cyclic pre-shearing increases stiffness, but limits suction pressure. • Suction and friction forces contribute equally to tensile response. • Uplift rate drives tensile behavior. [ABSTRACT FROM AUTHOR]

This paper presents the application of a novel discrete element-based method to simulate the continuous penetration process of jack-up foundations in various soil profiles. A special application of the linear contact bond model is proposed to reproduce the strength distributions of offshore clay. The calibrated inter-particle parameters accurately describe the sophisticated soil characteristics. The effects of particle size, boundary size, model scale, and penetration rate are investigated in this study. The established model balances the accuracy of the results and the computational efficiency. The results of the discrete element simulation are verified by comparison with three published examples. The numerical simulation results provide a microscopic perspective to understand the penetration process and show its advantages in coping with large deformation problems in geomechanics. • The discrete element method is used to simulate the penetration of foundations. • A complete description of the process of numerical implementation. • A special application of contact model is proposed to reproduce the clay strength. • The influence that some parameters may have on the numerical results is studied. • The accuracy of numerical results is verified against centrifuge experiments. [ABSTRACT FROM AUTHOR]

One of the biggest challenges faced by the offshore wave and tidal energy industry is the high cost of constructing and installing offshore foundations. Foundations based on post tensioned pile anchors can be effectively proposed to tackle this issue. A series of full-scale direct shear tests were performed on-shore to evaluate the shear resistance of post-tensioned pile anchor foundations designed for securing tidal turbine devices to a rock seabed. We focused, in particular, on the primary shear resistance mechanism of post-tensioned anchors, by applying a vertical force which mobilizes, a frictional force able to resist horizontal thrusts. Different load paths, involving monotonic or cyclic loading, were applied; several configurations for the footing of the foundation were tested. The footing stress-displacement behavior and the stress conditions at sliding failure from a number of different testing configurations were compared and analyzed. A marked consistency with the shear performance of natural rock joints was identified. This allows the behavior of tension pile foundations subjected to substantial horizontal loads to be modeled using relationships developed for rock joints, widely available in the literature. Additionally, the results obtained from different tests were also collated considering the various configurations adopted for the foundation-rock system and the applied load paths, to identify the factors that affect the shear resistance of the foundation. [ABSTRACT FROM AUTHOR]

Suction embedded plate anchors (SEPLAs) have been applied extensively in deepwater projects due to their high efficiency and low cost. In this paper, a new plasticity model was developed to simulate the keying behavior of SEPLAs. The model was based on three groups of yield envelopes, which considered three different states between the flap and the main plate. Thus, the plasticity model can consider the flap rotation relative to the fluke. The anchor shank was also considered to investigate the three dimensional (3D) effects of the actual SEPLA shape when deriving the yield envelops. A three dimensional large deformation finite element (3D-LDFE) model with flap rotation and shank considered was also set up. Then 3D-LDFE analysis was carried out to verify the plasticity model. The results given by 3D-LDFE analyses agree well with those by plasticity analyses. The effects of the flap on the embedment loss and pullout capacity, and the effects of loading eccentricity and pullout angle on diving behavior are investigated. Optimal padeye offset and pullout angle to drive the anchor diving are proposed. [ABSTRACT FROM AUTHOR]

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

The well-known p - y curve method provides soil-structure interaction that is independent of the load rate. In this paper an improved p - y curve method is proposed by considering the influence of the excitation frequency. For this purpose, a two-dimensional finite-element program is developed for analysis of a segment of an offshore monopile foundation placed in different depths. The intended use of the model is analyzes of offshore wind turbines in operation where small-magnitude cyclic response is observed in addition to the quasi-static response from the mean wind force. The response to small-magnitude cyclic loading is analyzed by employing coupled equations based on the u - P formulation, i.e. accounting for soil deformation as well as pore pressure. Thus, the paper has focus on the effects of drained versus undrained behavior of the soil and the impact of this behavior on the stiffness and damping related to soil-structure interaction at different load frequencies. In order to enable a parameter study with variation of the soil properties, the constitutive model is purposely kept simple. Hence, a linear poroelastic material model with few material parameters is utilized. Based on the two-dimensional model, linear p - y - y ̇ curves are extracted for the lateral loading of monopiles subjected to cyclic loads. The developed code is verified with findings in the literature. [ABSTRACT FROM AUTHOR]

Large offshore wind turbines are founded on jacket structures. In this study, an elastic full-space jacket structure foundation in an elastic and viscoelastic medium is investigated by using boundary integral equations. The jacket structure foundation is modeled as a hollow, long circular cylinder when the dynamic vertical excitation is applied. The smooth surface along the entire interface is considered. The Betti reciprocal theorem along with Somigliana's identity and Green's function are employed to drive the dynamic stiffness of jacket structures. Modes of the resonance and anti-resonance are presented in series of Bessel's function. Important responses, such as dynamic stiffness and phase angle, are compared for different values of the loss factor as the material damping, Young's modulus and Poisson's ratio in a viscoelastic soil. Results are verified with known results reported in the literature. It is observed that the dynamic stiffness fluctuates with the loss factor, and the turning point is independent of the loss factor while the turning point increases with load frequency. It is seen that the non-dimensional dynamic stiffness is dependent on Young's modulus and Poisson's ratio, whilst the phase angle is independent of the properties of the soil. It is shown that the non-dimensional dynamic stiffness changes linearly with high-frequency load. The conclusion from the results of this study is that the material properties of soil are significant parameters in the dynamic stiffness of jacket structures, and the presented approach can unfold the behavior of soil and give an approachable physical meaning for wave propagation. [ABSTRACT FROM AUTHOR]

Gravity installed plate anchor (GIPLA) is made mainly of steel plates. It features a swivel mooring arm located close to the anchor tip. Its more complex geometry inevitably complicates the prediction of its keying behavior, hence its capacity. This paper investigated the development of GIPLA׳s movements during its keying and its pullout capacity in NC clay. A plasticity model of yield envelops was constructed and used to predict anchor keying behaviors and its capacities. The plasticity model was validated by 3D large deformation finite element analysis based on remeshing and interpolation technique with small strain model. A parametric study on the keying and capacity development of a deeply embedded GIPLA in NC clay was performed by the plasticity model due to its simplicity and efficiency. The effects of anchor loading angle, anchor padeye eccentricity and soil strength profile were investigated. To encourage anchor “diving” behavior after keying and to keep anchor capacity reasonably high, it was recommended that the anchor loading angle to the horizontal at mudline should be 30° or less and the anchor padeye offset angle be in the range of 15°~25°. The soil non-homogeneity due to the linearly varying strength profile also affect anchor keying trajectory. [ABSTRACT FROM AUTHOR]

A suction pile has been regarded as an effective offshore foundation owing to its simple construction and removal. In this study, a group suction pile (i.e., a group format of a single-suction pile) was proposed to enhance the insufficient horizontal resistance given by a single suction pile. The effect of pile spacing on the horizontal resistance of the group suction pile under monotonic horizontal loading was evaluated. Group suction piles in a 3 × 3 arrangement were prepared with different pile spacings (2D, 3D, and 4D) and a large-scale soil chamber was used. The horizontal behavior of the group suction pile was analyzed by varying the loading positions. The effect of suction on the horizontal load response of the group suction pile was discussed. Particle image velocimetry (PIV) analysis was used to track the movement of the group suction pile in terms of horizontal movement, vertical movement, and rotation. The PIV analysis classified the failure modes of the group suction pile as forward overturning, backward overturning, and sliding. The results revealed that the rotational tendency during horizontal load testing governed the horizontal resistance of the group suction pile. • A group suction pile was proposed to enhance the insufficient horizontal resistance by a single suction pile. • The effect of pile spacing on the horizontal resistance of the group suction pile (3 × 3) was evaluated via particle image velocimetry (PIV). • The behaviors of group suction piles during loading were visualized and failure mechanisms were investigated. • The larger spacing is, the more stable behavior and higher resistance show. • Results revealed the rotational tendency during horizontal load testing governs the general behavior of the group suction pile. [ABSTRACT FROM AUTHOR]

As the offshore engineering moving from shallow to deep waters, the foundation types for fixed and floating platforms have been gradually evolving to minimize engineering costs and structural risks in the harsh offshore environments. Particular focus of this paper is on the foundation instability and its failure mechanisms as well as the relevant theory advances for the prevailing foundation types in both shallow and deep water depths. Piles, spudcans, gravity bases, suction caissons, and plate anchors are detailed in this paper. The failure phenomena and mechanisms for each type of foundations are identified and summarized, respectively. The theoretical approaches along with sophisticated empirical solutions for the bearing capacity problems are then presented. The major challenges are from flow-structure-soil coupling processes, rigorous constitutive modeling of cyclic behaviors of marine sediments, and the spatial variability of soil properties for large-spreading structures. Further researches are suggested to reveal the instability mechanisms for underpinning the evolution of offshore foundations. [ABSTRACT FROM AUTHOR]

Rapid uncontrolled leg penetration, or punch-through, accounts for a substantial number of accidents related to jack-up platforms, which are typically only employed at any one site for a few months before being removed and installed elsewhere. Hence, the ability to predict the load–penetration curve of a spudcan footing is particularly important in layered soil profiles, in order to identify punch-through risk prior to mobilisation of the rig. The correlation method proposed here links the spudcan load–penetration curve directly to the profile of cone tip resistance that is typically obtained as part of an offshore site investigation campaign. This contrasts with existing approaches that require input parameters that are empirically derived from site investigation measurements or necessitate additional soil element testing in an onshore laboratory. [ABSTRACT FROM AUTHOR]

Offshore wind turbine foundations are affected by cyclic loads due to oscillatory kinematic loads, such as those from wind, waves, and earthquakes. Monopiles are often used as a foundation concept for offshore windmill turbines. In this study, coupled dynamic equations with the u-P formulation for low-frequency load are considered for an offshore wind turbine monopile foundation, to present the response in terms of pore water pressure (PWP), stress and strain distribution in an elastic porous medium at regions around the monopile foundation. Different stress recovery techniques based on the Zienkeiwicz-Zhu (ZZ) error estimator namely, super-convergent patch recovery (SPR), weighted super-convergent patch recovery (WSPR), and L2-projection techniques are also investigated to recover the stresses at nodal points in the finite element method. To estimate errors in the time domain when performing transient simulations, three recovery processes are used with different meshes. The convergence of the dynamic problem is also studied. The results are verified with findings in the literature, revealing that the time period of effective stresses follows the applied load frequency. In conclusion, the history of the shear stress can have an important effect on the shear stress distribution, making it asymmetric in the time domain. [ABSTRACT FROM AUTHOR]

Saugrohrgründungen stellen eine alternative Gründungsmöglichkeit für Offshore‐Bauwerke dar. Sie können, im Gegensatz zu den in der Regel eingesetzten Rammpfählen, weitgehend schallemissionsfrei in den Baugrund eingebracht werden. Bei der Dimensionierung von Saugrohrgründungen spielen zyklische Einwirkungen aus Wind, Wellengang und Strömung eine besondere Rolle. Diese können zur Akkumulation von bleibenden Verformungen und Porenwasserüberdrücken in wassergesättigten Böden führen und sind deshalb innerhalb der Tragfähigkeits‐ und Gebrauchstauglichkeitsnachweise zu berücksichtigen. In diesem Beitrag wird das Tragverhalten des Boden‐Saugrohr‐Systems unter zyklisch axialen Druckeinwirkungen numerisch untersucht. In den FE‐Berechnungen wird ein Zwei‐Phasen‐Modell in Verbindung mit einem hypoplastischen Stoffgesetz für den wassergesättigten Boden verwendet. Besondere Aufmerksamkeit wird dabei den Wechselwirkungen zwischen der Struktur, dem wassergesättigten Meeresboden und dem Porenwasser gewidmet. Der Einfluss und die Relevanz einiger der wichtigsten System‐ und Einwirkungsparameter, die die Porenwasserdruckentwicklung in wassergesättigten Böden beeinflussen, werden auf der Basis von parametrischen Studien untersucht. Darin werden die Zyklenanzahl, die Frequenz der zyklischen Einwirkung, die Einbindelänge sowie der Kopfplattendurchmesser des Saugrohres variiert. Der Einfluss von Akkumulationseffekten auf das interaktive Tragverhalten des Saugrohr‐Boden‐Systems Numerical investigations on the behaviour of suction bucket foundations under cyclic axial compressive loads Suction buckets are an alternative foundation type for offshore structures. Due to their widely noise emission‐free installation, they can be used instead of usual offshore foundations with driven piles. Cyclic loads induced by wind, water waves and currents play a special role for the design of suction bucket foundations. These loads can lead to an accumulation of permanent soil deformations and excess pore water pressures in water saturated soils. This has to be considered in ultimate limit state and serviceability design. In this paper the interaction behavior of soil‐bucket‐systems subjected to cyclic axial compressive loads is analyzed using a finite element model. A fully coupled two‐phase model and a hypoplastic constitutive model for the water saturated soil are used in the numerical analyses. Special attention will be dedicated to interactions between the structure, the water‐saturated soil and the pore water. The influence and relevance of some of the main system and loading parameters that affect the pore water pressure development in water‐saturated soil are studied on the basis of parametric studies. In there the cyclic loading number, the frequency, the embedded length and the diameter of top plate of the bucket are varied. Based on these investigations the importance and relevance of the consideration of cyclic accumulation effects with soil‐bucket‐systems is demonstrated and the key findings are presented. [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. [ABSTRACT FROM AUTHOR]

Die Entwicklung kosteneffektiver Offshore Gründungsstrukturen ist notwendig, um die 'Energiewende' erfolgreich voranzutreiben. Aufgezeigt wird, wie im Rahmen des BIONA-Projekts 'Offshore Foundation nach dem Verfahren ELiSE' eine gewichtsoptimierte Gründungsstruktur einer Offshore Windenergieanlage mithilfe des Verfahrens 'Evolutionary Light Structure Engineering' (ELiSE) entwickelt wurde. Dazu schlossen sich die Unternehmen WeserWind GmbH, RLE International GmbH und das Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung zusammen, um mit den vorhandenen Kompetenzen in den Bereichen Strukturleichtbau, Produktionsplanung und Finite-Elemente-Simulationen eine neuartige Gründungsstruktur zu konzipieren. Den Ausgangspunkt für die Neuentwicklung bildeten die Geometrien von Planktonorganismen, deren Prinzipien neue Strukturlösungen lieferten. Technisches Ziel des Projekts war es, durch die Nutzung von biologischen Bauprinzipien eine Gründungsstruktur beispielhaft für eine 5-MW-Anlage zu entwickeln, die gegenüber den bisher genutzten Bauten eine signifikante Verbesserung insbesondere bezüglich Materialeinsatz, aber auch hinsichtlich Fertigung und Montage bei mindestens gleicher Tragfähigkeit aufweist. Wissenschaftliches Ziel waren Einsatz und Erweiterung des bionischen Leichtbau- und Optimierungsverfahrens ELiSE, um einen neuen Weg zur Entwicklung radikal verbesserter Leichtbaukonstruktionen zu untersuchen. Durch die Anwendung des ELiSE-Verfahrens konnten die Prinzipien der Natur extrahiert und für die Entwicklung einer neuartigen, leichten und potentiell kostengünstigen Gründungsstruktur erfolgreich eingesetzt werden. Exemplarisch soll indiesem Artikel dargestellt werden, welche Schritte unternommen wurden, um die Zielsetzungen des Projekts zu verwirklichen. Offshore foundation with the method ELiSE The development of cost-effective structures for new offshore foundations is an important factor to advance the 'Energiewende'. Within the BIONA-project 'Offshore Foundation with the method ELiSE', it is shown how the structure of a foundation of an offshore wind energy plant was developed and optimized in weight by using the method 'Evolutionary Light Structure Engineering' (ELiSE). The companies WeserWind GmbH, RLE International GmbH and the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research came together to design a new lightweight structure using their existing expertise in the areas of structural lightweight design, production planning and finite element simulations. The new development in the field of lightweight design is based on the stable and yet light shells of planktonic organisms which served as archetype for the technical design process. The project had two main goals: the development of a foundation for a 5-MW wind energy plant for the offshore application in deeper waters by using principles from nature was the technical objective of the project. The design of the foundation had to be characterized by efficient material usage, good manufacturability and economic aspects. In addition, the load capacity of the structure had to stay at least at the same level of traditional design solutions. The scientific objective was the usage of the bionic lightweight method ELiSE to investigate a new way of developing radically improved lightweight constructions. By applying ELiSE, lightweight principles were successfully identified in the biological archetypes and transferred to a technical solution. As a result, a new offshore foundation was designed which can be characterized by both lightweight and cost-effectiveness. In this article, the necessary steps of the development of this bionic offshore foundation are exemplarily demonstrated. [ABSTRACT FROM AUTHOR]

Abstract: To improve the moment fixity and increase the horizontal capacity of the shallow foundations for offshore structures, the spudcans are fitted with peripheral skirts and, often, internal skirts. The guidelines relevant to skirted spudcans acknowledge the increase in bearing capacity and in some cases, recommend solutions for embedded and skirted footings. In the current study, the undrained bearing capacity of the skirted spudcan foundation, on both homogeneous and heterogeneous soil, subjected to combined vertical (V), horizontal (H) and moment (M) loading is assessed by means of finite element analysis (FEA) and compared to known capacities for both conventional spudcans and circular skirted foundations. The improved capacity of the skirted spudcans to the conventional ones is evident and compares fairly with that of the skirted mats on homogeneous soil. Solutions for skirted spudcans on heterogeneous (normally consolidated) soil are also provided and interpreted. [Copyright &y& Elsevier]

Abstract: Offshore foundations are subject to combinations of vertical, horizontal and moment (VHM) loading. Different foundation solutions are appropriate, depending amongst others, on the expected load combinations. This paper investigates in detail the soil failure mechanisms and resulting foundation capacity under undrained VHM loading of a hybrid foundation concept. Comprising of a skirted mat combined with an internal caisson compartment, this foundation design is found to provide significantly increased horizontal capacity that is often critical in offshore applications, with key influences for increased moment capacity identified as well. The numerical study investigated both variations in the geometry of the internal caisson compartment and the soil shear strength profile. The paper concludes by proposing expressions that allow slightly conservative prediction of the combined capacity of a hybrid foundation. [Copyright &y& Elsevier]

Abstract: Plate anchors, such as suction embedded plate anchors and vertically driven plate anchors, offer economically attractive anchoring solutions for deep/ultra-deep water offshore developments. The rotation/keying processes of plate anchors will cause embedment losses, which lead to decreases of the uplift resistances of the anchors in normally consolidated soil. In the present paper, the keying processes of vertically installed strip and square plate anchors are simulated using the 3-D large deformation finite element method. The effects of loading eccentricity and pullout angle on the embedment loss during keying are investigated. Both the development of the uplift resistance and the soil flow mechanisms are presented. The numerical results show that the loading eccentricity e/B has a much larger effect on the embedment loss than the pullout angle does. The anchor shape has a minimal effect on the loss in anchor embedment. The shape factors (square/strip) are 1.05–1.09 for loss of embedment and 1.10–1.19 for capacity. [Copyright &y& Elsevier]

Structural health monitoring for offshore wind turbine foundations is paramount to the further development of offshore fixed wind farms. At present time there are a limited number of foundation designs, the jacket type being the preferred one in large water depths. In this work, a jacket-type foundation damage diagnosis strategy is stated. Normally, most or all the available data are of regular operation, thus methods that focus on the data leading to failures end up using only a small subset of the available data. Furthermore, when there is no historical precedent of a type of fault, those methods cannot be used. In addition, offshore wind turbines work under a wide variety of environmental conditions and regions of operation involving unknown input excitation given by the wind and waves. Taking into account the aforementioned difficulties, the stated strategy in this work is based on an autoencoder neural network model and its contribution is two-fold: (i) the proposed strategy is based only on healthy data, and (ii) it works under different operating and environmental conditions based only on the output vibration data gathered by accelerometer sensors. The proposed strategy has been tested through experimental laboratory tests on a scaled model. [ABSTRACT FROM AUTHOR]

As offshore structures grow larger with increasing depth and distance from shore, their foundations must increase in strength owing to the larger supporting capacity needed. This requires new approaches to ensure economic and reliable infrastructure. Suction bucket foundations (SBFs) are viable options in offshore settings owing to their easy installation and affordability; however, they suffer from performance limitations. Recently, a hybrid bucket foundation (HBF) design has been proposed in which a suction bucket is connected to an underlying mat to increase load capacity. However, the behavior of this design under combined vertical, horizontal, and/or moment loads is not yet well understood. In this study, we used centrifuge models to investigate the behavior of HBFs and conventional SBFs under different load conditions. The results demonstrated the feasibility and superior performance of HBFs. In particular, the bearing capacities of HBFs under vertical and combined loads were ~1.91 and ~1.82 times higher, respectively, than those of SBFs within the testing ranges. These findings indicate that the mat component attached on top of the hybrid bucket unit significantly improves the bearing capacity. [ABSTRACT FROM AUTHOR]