The design of monopile foundations for offshore wind turbines is often governed by lateral tilt under monotonic and cyclic loading, commonly assessed using distributed (spring-based) soil-reaction models. While these models are well established for monotonic loading, their extension to cyclic conditions – and their acceptance in industry – remains limited. As part of a broader research programme on cyclic soil-reaction modelling, this paper supports such developments through non-linear 3D FE analyses of monopile response in sand under monotonic and cyclic loading. The SANISAND-MS constitutive model is employed to capture the drained cyclic behaviour of the sand, including ratcheting. Extensive parametric studies are performed to investigate the combined effects of geometric, geotechnical, and loading conditions. The results confirm well-known aspects of monopile mechanics while also highlighting less-studied features, including the relative contributions of different (cyclic) soil-reaction components (within the PISA framework) and the quantitative influence of relative monopile-soil stiffness on both monotonic and cyclic response. Finally, the study proposes interpolation laws synthesising the numerical findings, which can aid in conceptualising monopile lateral behaviour, guiding future experimental campaigns, and, very importantly, informing the development and validation of simplified soil-reaction models.

Understanding and accurately modelling monopile behaviour is a central challenge in modern offshore wind geotechnics, often requiring, for detailed design, robust finite-element (FE) simulations supported by well-calibrated constitutive models. This study critically evaluates and advances the application of 3D FE modelling for laterally loaded monopiles using the SANISAND-MS model, informed by a comprehensive experimental programme ranging from element-scale testing to centrifuge modelling under both monotonic and cyclic loading, in dry and saturated sand. This work investigates strategies for the reliable calibration of the SANISAND-MS constitutive model. Key calibration challenges are addressed, including limitations in test data availability, variability in material response, and the alignment of model parameters with soil strain levels representative of realistic operational scenarios. The study further highlights practical considerations and limitations associated with the use of SANISAND-MS, particularly when extrapolating features of foundation response observed in physical modelling to full-scale conditions. For the cases considered herein, comparisons between numerical simulations and experimental data show good agreement in dry conditions, whereas reduced accuracy in saturated cases underscores the need for a more detailed treatment of, among other factors, soil–pile interface behaviour and loading-rate effects on excess pore water pressure generation. Overall, the findings provide valuable guidance for improving the fidelity of advanced FE simulations for offshore monopile design.

Monopiles are the most common foundation for offshore wind turbines (OWTs), accounting for roughly 80% of installations in Europe. Despite advancements in research, critical knowledge gaps remain, especially regarding the behaviour of monopiles under long-term cyclic loading. Addressing these gaps is vital for enhancing the safety and costeffectiveness of future offshore wind farms and for assessing the life-cycle conditions of existing OWTs. The "MIDAS: Monopile Improved Design through Advanced Cyclic Soil Modelling" project, conducted in the Netherlands by TU Delft, Deltares, NGI, and industry partners, aimed to fill these gaps. Focusing on sandy soils, MIDAS employed a comprehensive methodology combining experimental (element and centrifuge testing), numerical, and theoretical modelling. This paper presents the centrifuge modelling component, detailing the design and implementation of the testing program, including cyclic load definitions, model pile instrumentation, loading configurations, model seabed preparation, and test procedures. Findings indicate that monotonic responses of monopiles with different configurations can be normalized effectively, validating the quality of experimental outcomes in the context of established theoretical models. The study also explores the impacts of stress levels, monopile dimensions, and drainage conditions on cyclic behaviour, contributing valuable insights to the understanding of monopile-soil interactions under cyclic loads.

This paper presents an investigation into the suitability of the SANISAND-MS model for the three-dimensional finite-element (3D FE) simulation of cyclic monopile behaviour in sandy soils. In addition to previous work on the subject, the primary focus of this study is to further assess the model's capability to reproduce the accumulation of permanent deflection/tilt under cyclic lateral load histories. To this end, experimental data from the PISA field campaign are employed, particularly those emerged from the medium-scale cyclic tests conducted at the Dunkirk site in France. The methodology adopted herein involves calibrating the SANISAND-MS model's parameters to align with 3D FE simulation of a selected monotonic pile test reported by the PISA team using a bounding surface plasticity model partly similar to SANISAND-MS. Subsequently, the soil parameters governing SANISAND-MS’ ratcheting response are calibrated using only minimal information from published PISA field data. While representing the first attempt to simulate the reference data set using a fully ‘implicit’ 3D FE approach, this paper offers novel insights into calibrating and using advanced cyclic models for monopile analysis and design – particularly, with regard to the quantitative influence of pile installation effects and sand's microstructural evolution under drained cyclic loading.

Predicting the non-linear loading response is the key to the design of suction caissons. This paper presents a systematic study to explore the applicability of deep learning techniques in foundation design. Firstly, a series of three-dimensional finite element simulations was performed, covering a wide range of embedment ratios and different loading directions, to provide training data for the deep neural network (DNN) model. Then, hyper-parameter tuning was performed and it is found that the basic Fully-Connected (FC) neural network model is sufficient to capture the non-linear response of suction caissons with excellent accuracy and robustness. Furthermore, the optimized FC neural network model was also successfully applied to a database of suction caissons in sand, demonstrating its broad applicability. By comparing three typical DNNs, i.e., FC, Convolutional Neural Network (CNN) and Long Short-Term Memory (LSTM), it was observed that the FC neural network model excels over others in terms of simplicity, efficiency and accuracy. More importantly, by looking into the model's generalization performance, the FC neural network model can also identify the change in foundation failure mechanisms. This study demonstrates the DNN's powerful mapping ability and its potential for future use in offshore foundation design.

The decommission of cables or pipelines is a vital aspect which ensures a sustainable and effective process of the infrastructure life cycle. Ideally, all offshore installations and equipment should be removed entirely but, in some cases, some flexibility is provided by the international (or national) laws or regulations whether the total removal might induce extreme risk, cost, or adverse environmental damage. The development of technology that facilitates pipeline or cable decommissioning is of vital importance. A newly developed concept of a decommissioning tool has just proposed by Enersea. This novel tool is placed into the pipeline (or over the cables) and induces vibrations in the structure and the surrounding soils, which result in a lower uplift resistance of the pipeline or cable. This paper presents the feasibility study of this technique for a cable/pipeline buried in sand. It is illustrated if it is possible to induce soil liquefaction in the vicinity of the buried pipeline/ca-ble, and the length of the pipeline affected by the liquefiable zone is also presented.

Gentle driving of piles (GDP) is a new technology for the vibratory installation of tubular (mono) piles that aims to achieve both efficient installation and low noise emission by combining axial and torsional vibrations. To provide a preliminary demonstration of the GDP concept, onshore medium-scale tests in sand were performed in late 2019 at the Maasvlakte II site in Rotterdam (Netherlands). Several piles were installed using both impact and vibratory driving methods (including GDP), with the twofold aim of comparatively assessing (1) the effectiveness of GDP; and (2) the presence of installation effects in the pile response to lateral loading. This work focuses on the latter aspect and presents a quantitative analysis of the installation effects observed in the pile loading test data recorded in the field. Due to soil inhomogeneity across the field, a purely data-based analysis would have not supported objective conclusions, which led to adoption of an alternative approach based on one-dimensional (1D) numerical modeling. To this end, an advanced cyclic p-y model was calibrated for the simulation of the reference pile loading tests, and the values of key parameters were compared to infer quantitative information about relevant installation effects. The results presented herein inform about the promising performance of the GDP method, particularly in comparison to traditional impact hammering. Although the cyclic lateral pile behavior proves affected by the installation process, certain important aspects of installation effects gradually diminish as more loading cycles are applied.

Gentle Driving of Piles (GDP) is a new technology for the vibratory installation of tubular (mono)piles. Its founding principle is that both efficient installation and low noise emission can be achieved by applying to the pile a combination of axial and torsional vibrations. Preliminary development and demonstration of the proposed technology are the main objectives of the GDP research programme. To this end, onshore medium-scale tests in sand have been performed on piles installed using both impact and vibratory driving methods (including GDP). After presenting the development of a purpose-built GDP driving device and the geotechnical characterisation of the site, this paper covers the execution of GDP installation tests. Focus is on the installation performance of GDP-driven piles, which is discussed with the aid of structural and ground monitoring data. The comparison between piling data associated with GDP and standard axial vibro-driving points out the potential of the proposed installation technology, particularly with regard to the beneficial effect of the torsional vibration component. The findings of this study encourage further development of the GDP method and its future extension to offshore full-scale conditions.

Gentle Driving of Piles (GDP) is a new technology for the vibratory installation of tubular (mono)piles. Its founding principle is that both efficient installation and low noise emission can be achieved by applying to the pile a combination of axial and torsional vibrations. Preliminary development and demonstration of the proposed technology are the main objectives of the GDP research programme. To this end, onshore medium-scale tests in sand have been performed on piles installed using both impact and vibratory driving methods (including GDP). While the results of the installation tests are presented by Tsetas et al. (2023), this work focuses on the post-installation performance of GDP-driven piles under a sequence of slow/large-amplitude (cyclic) and faster/low-amplitude (dynamic) load parcels. The field data point out the influence of onshore unsaturated soil conditions, which result in complex cyclic pile stiffness trends due to the interplay of pile–soil gapping and soil's fabric changes. The pile stiffness under small-amplitude vibrations is strongly correlated with the previous response to large load cycles, and noticeably frequency-dependent for load cycles with a period lower than 1 s. Overall, the post-installation performance of GDP-driven piles appears to be satisfactory, which encourages further development and demonstration at full scale.

Offshore monopile foundations are exposed to misaligned wind and wave loadings, which are respectively dominated by (nearly) static and cyclic load components. While the response of these systems to unidirectional cyclic loading has been extensively investigated, only a few studies have been devoted to the realistic case of misaligned static and cyclic loads, and particularly to the effects of such misalignment on the accumulation of pile rotation under prolonged cycling. This paper presents a 3D finite-element (FE) modelling study on the relationship between load misalignment and cyclic monopile tilt under drained conditions, based on the use of the SANISAND-MS model to enable accurate simulation of cyclic sand ratcheting. After qualitatively identifying the relationship between relevant loading parameters and cyclic stress/densification mechanisms in the soil, specific parametric studies are performed to explore the impact on pile tilt accumulation. The results show that, in comparison to unidirectional loading, misaligned static–cyclic loading gives rise to lesser-known pile–soil interaction mechanisms: when the direction of cycling deviates from that of the static load, “cyclic compression” and “direct cyclic shearing” mechanisms begin to co-exist. This is quantitatively captured by a newly proposed empirical equation for monopile tilt calibrated against the 3D FE simulation results obtained in this work.

The response of monopiles to lateral loading has attracted considerable research interest in recent years. As monopile foundations are exposed to ever-harsher environmental conditions, the engineering tools used for their simulation should continually update and improve. Recently, the challenge of simulating the behaviour of monopiles under lateral loads has been addressed to a significant extent through a combination of numerical modelling and experimental data. Although monotonic response calculations are still relevant to monopile design, it should be acknowledged that offshore environmental loads are inherently cyclic. To improve the engineering tools for the simulation of cyclic monopile behaviour and our understanding of the relevant geotechnical mechanisms, this study presents and discusses the outcome of advanced 1D cyclic soil reaction modelling of monopile-soil interactions employed to simulate centrifuge data conducted as part of the MIDAS research project. The memory-enhanced p-y model proves capable of simulating cyclic ratcheting behaviour in complex loading histories, which promotes the discussion for the evolution of relevant soil reaction mechanisms during cyclic loads. Finally, preliminary calibration strategies for the employed cyclic soil reaction models are presented.

A hybrid material point/finite volume method for the numerical simulation of shallow water waves caused by large dynamic deformations in the bathymetry is presented. The proposed model consists of coupling the nonlinear shallow water equations for the water flow and a dynamic elastoplastic system for the seabed deformation. As a constitutive law, we consider a linear elastic-non-associative plastic model with the Drucker-Prager yield criterion allowing for large deformations under undrained cases. The transfer conditions between these models are achieved by using forces sampled from the hydraulic pressure and the friction terms along the interface between the seabed soil and shallow water. A detailed description regarding the coupled algorithm for the hybrid material point/finite volume method is presented. Several numerical examples are investigated to demonstrate the performance of the finite volume method for simulations of shallow water flow and the material point method for capturing the large deformation process of the solid phase. We also present numerical simulations of an undrained clay column collapse that induced shallow water waves and a dam-break problem to demonstrate the excellent performance of the proposed hybrid material point/finite volume method.

Presented here is a numerical study on the preloading of four-legged jack-ups, such as those commonly employed in the construction of offshore wind farms. The need for reducing jack-up installation time is particularly felt within the offshore industry, especially when multiple preloading cycles are necessary in clayey soils to fulfil given preloading criteria. This is due to clays experiencing delayed deformations, causing load redistribution among all legs while the ideal situation of steady preload on all spudcans is pursued. This work employs three-dimensional finite element (3D FE) modelling to analyse the preloading performance of a reference jack-up vessel in clayey soils using a wished-in-place (WIP) approach. Detailed modelling of time effects due to soil consolidation and viscosity is introduced, with some emphasis on how to derive material parameters from typical site investigation and laboratory soil data. The results of specific parametric studies are presented to support the suitability of the adopted analysis approach, also with regard to the adoption of alternative preloading procedures. The constitutive modelling of time-dependent clay’s behaviour is shown to play a crucial role in the considered framework, and will require further research for 3D FE modelling to provide reliable quantitative support to real wind farm installation projects.

The vibratory installation of monopiles as foundation for offshore wind turbines is considered a plausible solution next to the conventional installation method (impact-hammering). One of the main advantages is the lower noise emissions, reducing harm to the marine life. However, knowledge on the effects of the vibratory installation parameters on the lateral response of monopiles – and how these effects differ from those caused by impact-driving – is limited. This paper presents the results from an ongoing Joint Industry Project (SIMOX) with focus on 1g laboratory tests carried out in a 9.0m x 5.5m x 2.5m tank with saturated sand at Deltares, the Netherlands. The tests involve the installation (impact and vibratory) of scaled piles with 32 cm diameter, embedment length of 1.5 m and two wall thicknesses. The lateral loading regime consisted of monotonic and cyclic lateral loading. The results show the effect of soil density and different installation parameters of vibratory installation on the lateral response of the piles compared to a conventional impact installation.

Since the industrial revolution, humanity's impact on the planet has increased significantly. The growth of global economies and population size in the 20th century was fueled by the combustion of fossil fuels. In an effort to reduce the impact of human kind on the environment, governments ratified landmark agreements such as the Montreal Protocol in 1987, the UNFCCC in 1992, the Kyoto Protocol in 2005, and the Paris Agreement in 2015. To support this effort, the European implemented the European Green Deal (2019), which aims to achieve no-net greenhouse gas emissions by 2050. Offshore wind energy, particularly large-diameter monopiles, is expected to play a substantial role in this transition. Europe has already developed over 28 GW of offshore wind power, with a global capacity of 37 GW as of 2021. However, to meet the goals of the European Green Deal, offshore wind capacity needs to scale up significantly in the next 28 years. The installation of monopiles, the most selected foundation option for offshore wind turbines, has traditionally relied on impact hammering. This method has drawbacks such as lengthy installation times, and noise emissions harmful to marine life. An alternative approach is axial vibratory pile driving, which offers faster and quieter installation. However, certification bodies have yet to endorse its use for offshore wind farm construction owing to uncertainties relating to the post-installation monopile performance. Research efforts are being devoted to understanding the dynamic behaviour of the soil during vibro-driving and the effects of vibro-installation on pile performance. Several geotechnical research teams are investigating the post-installation lateral behaviour of monopiles and comparing the performance of impact piling and vibratory piling. To complement the effort towards noiseless pile driving researchers from TU Delft proposed the novel Gentle Driving of Piles (GDP) method which aims to enhance traditional axial vibro-pile driving by incorporating high-frequency torsional vibrations. The addition of torsional vibrations is expected to consume/redirect soil frictional resistance and limit radial expansion during pile driving, resulting in faster and quieter installation.

To accommodate the foreseen expansion of the offshore wind sector, monopile-supported Offshore Wind Turbines (OWTs) are currently being designed for harvesting offshore wind energy in seismically active regions. Three-dimensional (3D) Finite Element (FE) analyses have proven a reliable, though computationally expensive, tool for modelling laterally loaded monopiles. A more efficient modelling approach is the one-dimensional (1D) Beam-on-Winkler-Foundation (BWF) method, where the monopile is modelled via a series of beam elements, laterally supported by uncoupled, lateral soil springs. Under the simplifying assumption of linear elastic soil behaviour, this study explores the suitability of the BWF method for the simulation of the seismic soil-structure interaction by comparing the response obtained through 1D modelling to the outcome of 3D FE calculations. To this end, different monopile geometries are examined, for which the contributions of multiple soil resisting mechanisms (determined by normal and tangential stresses along the pile shaft and base) to the global monopile response are also assessed.

This paper uses 3D numerical analyses to investigate the stress path experienced by soil elements around large diameter piles in sand subjected to monotonic drained lateral loading. Inspection of the loading-induced stresses in the soil revealed the multiaxial nature of these stress paths, which are characterised by rotation of one or more principal stress axes. Based on the outcome of the finite element analyses, typical stress paths for different soil elements around the piles are extracted. Such stress paths are then evaluated against those enabled by conventional and advanced laboratory soil element testing. It is found that a combination of tests in the Hollow Cylinder Torsional Apparatus (HCTA) can reproduce most features of the numerically identified stress paths for soil elements around the pile. Unavoidable limitations in laboratory testing are discussed as well as the major challenge in replicating the loading direction with respect to the material axes. Some guidance for the experimental implementation of these stress paths in the HCTA are provided as well as a discussion on the use of conventional experimental equipment, such as the conventional triaxial or simple shear apparatus.

Predicting the nonlinear load response of caisson foundations is critical to the foundation design. Despite extensive studies aimed at developing models for predicting the combined V-H-M bearing capacity of suction caissons in clay, accurately predicting the three-dimensional (3D) deflection response of the foundation remains a significant challenge. In this paper, we present a novel solution by developing a fully connected (FC) neural network model that enables load-deflection prediction of suction caissons on clay. To train and evaluate the FC model, a series of 3D finite element simulations were performed covering caissons responses with an embedment ratio of up to 1. The effect of various model hyperparameters on the model's prediction accuracy and generalisation ability was systematically investigated. The results show that the proposed model achieves load-deflection response prediction with simplicity, efficiency and accuracy, demonstrating the significant potential of deep learning technology in the geotechnical design of foundations.

Monopiles are the predominant type of foundation used for offshore wind turbines. The increase in size of monopiles and the stricter environmental regulations in terms of underwater noise levels has motivated the development of alternatives to the conventional impact-driving method of monopile installation. One of the alternatives is the (axial) vibratory installation, which has been previously studied in field [1, 2, 4] and laboratory [3, 5] conditions. However, there is limited knowledge on the effects of vibratory installation (and how these effects differ from those caused by impact-driving) on the lateral response of monopiles. This extended abstract presents the results of an ongoing Join Industry Project (SIMOX – Sustainable Installation of XXL Monopiles) which aims at comparing different installation methods from the point of view of driveability, noise emissions and lateral response. The present abstract particularly focuses on the lateral response of monopiles. As a first step towards the large-scale onshore field tests to be executed in 2023, a laboratory study was conducted at the Water-Soil Flume at Deltares, in Delft (NL), which consists of a tank with 9.0 m of length, 5.5 m of width and 2.5 m of depth, with a multipurpose wagon on rails above it.

Offshore monopiles accumulate permanent tilt under long-lasting cyclic environmental loads. Accurate prediction of monopile tilt is key to assessing their serviceability, and requires a fundamental understanding of loading history effects. While both experimental and numerical studies are shedding light on this matter, this work uses step-by-step implicit 3D FE modelling to investigate loading history effects in the response to cyclic lateral loading of monopiles in sand and to identify links between local soil behaviour and relevant features of global pile behaviour. For this purpose, the recently developed SANISAND-MS model is adopted to achieve a reliable simulation of sand's cyclic ratcheting. In particular, the validity of an up-scaled Miner's rule for monopile tilting under multi-amplitude cyclic loading is assessed based on the results of 3D FE parametric analyses, with emphasis on the role played by the engineering idealisation of random environmental loading. The validity of such a rule has been numerically investigated both in terms of local soil element response and global foundation behaviour — for the particular case of a large-diameter monopile. In respect, the effect of the loading history idealisation is presented, and it is concluded that Miner's rule does not always rigorously apply to all the cases considered herein. The translation of irregular loading histories into a regular version with loading packages sorted in ascending amplitude order is shown to be a reasonable approach, at least when the possibility of cyclic pore pressure build-up is disregarded.