The Horizon Europe research project TAILWIND aims to advance station-keeping system technologies for floating offshore wind farms. This paper marks the first steps in the project putting forward economic, environmental, and technological key performance indicators to assist the selection and development of anchors. Scenarios in terms of location, soil profile, and floater are defined. Anchor loading histories are obtained through coupled load simulations and used to design typical anchors. Key performance indicators describing three sustainability aspects – economic, environmental, and technological – are proposed to assess the industrial feasibility of each anchor type. The study has two outcomes. Firstly, sustainability key performance indicators that can guide the selection of anchor technologies for future floating offshore wind development are proposed. Secondly, guidance on the most promising anchor for further development via experimental testing and numerical modelling within the TAILWIND project is provided.

As the global transition to renewable energy accelerates, ensuring the reliability of foundations in offshore structures is increasingly important. In the context of floating wind structures, pile foundations can be used as anchor points for station keeping against significant cyclic loading. Tubular piles have proven reliable while offering a high tensile load capacity, but accurate predictions of pile tensile capacity and stability without extensive testing are essential to avoid overconservative design. This paper presents findings from the Tubular Pile Pull-out Testing (TPPT) Joint Industry Project, which involved field testing on tubular steel piles under monotonic and multi-stage cyclic loading at the Port of Rotterdam. This paper primarily discusses the comparison between predicted and measured pile capacity and stability under cyclic loading. The predictions were based on interaction charts recommended in the literature for piles under tensile loading. Pile responses in interaction charts are classified as stable, metastable, or unstable based on their displacement responses to the applied cyclic loading in relation to the static capacity. The results observed in the field tests are compared with the stability response previously defined in the literature. In particular, the TPPT testing programme included tests near the chart zone where stable and metastable curves converge towards the unstable zone, where the proximity between curves leads to uncertainties in determining pile stability.

Driven pipe piles are used extensively in coastal and offshore projects. Traditionally piles with diameters of 2–3 m were common in the offshore wind industry, however the diameter of monopiles to support a 10 MW wind turbine is more commonly 10 m. Offshore wind projects are being developed at sites with very low seabed strengths and pipe pile weights are increasing significantly. Self-weight penetration occurs when the pile is first placed on the seabed. A combination of low strength seabed conditions and increased pile self-weight leads to the risk of pile run (uncontrolled self-weight penetration) during installation at some sites. Predicting pile run risk, run velocities and penetration depths is challenging due to inherent rate effects and the large strains involved. While rapid penetration processes can be considered using both analytic methods and Large Deformation Finite Element simulations, the role of soil rigidity is seldom taken into account, despite known implications from static pile assessments. This study uses large deformation simulation with the Coupled Eulerian Lagrangian method to simulate the pile running process for five well-studied fine-grained soils with varying elastic stiffnesses. Results are compared with analytic methods, highlighting the limitations of current predictive techniques in terms of both the end tip and shaft resistance. As a corollary, a linear trend for the final penetration depth with respect to the logarithm of the soil rigidity index is incorporated in an existing analytic code based on results obtained from large deformation simulations.

The goal of this study is to investigate the effect of model parameters on the behaviour of offshore wind turbines in liquefiable soils under earthquake loading. Numerical analyses were conducted using an advanced soil constitutive model for liquefaction behaviour, the P2PSand model, available in FLAC3D. A previous study was chosen from the literature to verify the created numerical model, comparing pore water pressure in the soil and horizontal displacement of the monopile. The results indicate that the model can accurately predict both soil and pile behaviour. After validation, a new model was created to assess the effect of liquefiable soil parameters. Three soils were selected for comparison: Ottawa sand, Karlsruhe fine sand, and standard cyclic resistance field (SCRF) sand. Calibration of the model parameters for these soils is well-documented in the literature. A single earthquake record was applied to the model base, and the responses of free-field ground acceleration at the surface, superstructure (tower) acceleration, and pile head rotation were compared. Results showed that offshore wind turbine response in liquefiable soils is strongly influenced by soil parameters. Particularly, the parameters of SCRF sand led to higher ground and tower accelerations, resulting in greater monopile head rotations.

Evaluating long-term building reconstruction is essential to strengthen resilience to earthquakes. Field investigations provide detailed and accurate information for building assessments, but are often labour intensive, costly, and time consuming, particularly when considering the regional-scale impact of earthquakes. In contrast, satellite Remote Sensing (RS) techniques provide frequent data across vast areas, making them ideal for regional-scale post-earthquake assessments, which can complement field surveys. Despite this, most RS studies have relied on manual change detection of satellite data before and after the event, limiting their potential for automated assessment and reducing their support for field investigations. In this study, we developed a novel RS method designed to assist field investigations of post-earthquake building reconstruction on a regional scale. The method automatically identifies target buildings for field teams to investigate, locating collapsed structures or buildings that have changed due to post-earthquake reconstruction efforts. We applied Multi-Temporal Synthetic Aperture Radar Interferometry (MT-InSAR) for the first time to evaluate post-earthquake building reconstruction. The proposed method involves a two-stage analysis: first, a grid-level assessment on a regional scale to detect areas with reconstruction activities following an earthquake, and then a detailed building-level analysis to identify individual buildings that have undergone changes as part of the reconstruction process within these areas. The method was used to assess building reconstruction efforts in Nepal after the 2015 Gorkha earthquake. For the MT-InSAR analysis, we acquired two stacks of 3-m-resolution SAR images, one before and one after the earthquake. The grid-level analysis detected multiple urban areas with significant changes, which were then subjected to a building-level analysis. This analysis pinpointed the locations of affected buildings and determined the extent of changes related to reconstruction activities. A comparison of the building-level results with field observations confirmed that the method successfully identified buildings that have undergone changes. These changes included buildings that were left in a collapsed state, demolished, under construction, or fully reconstructed. The MT-InSAR-based approach introduced in this study has the potential to serve as a valuable tool to guide future field surveys related to post-earthquake reconstruction, significantly reducing the time and effort needed for such assessment.

This study reviews existing cone penetration test (CPT) correlations for the prediction of the small strain shear modulus (Gmax). Its performance is investigated through application to an open-source offshore ground investigation dataset from the Netherlands. The research evaluates correlations involving various parameters such as cone tip and corrected cone tip resistance, net corrected cone resistance, sleeve friction, pore water pressure, and vertical effective stress. Results indicate that correlations are highly site-specific, often requiring recalibration to account for local conditions. Existing sand correlations provide more accurate predictions but tend to underpredict Gmax, while clay-specific correlations tend to overpredict Gmax, particularly in stiffer offshore clays. The study also highlights the need for further exploration of parameter normalisation to refine these correlations. This work represents an additional step in the understanding of CPT-based Gmax predictions and their associated uncertainties, emphasizing the importance of developing robust, site-specific correlations for optimal offshore wind foundation design.

Quay walls are often assessed using numerical models to capture highly nonlinear soil behavior and the complex interactions between foundation elements. The input parameters of these models are usually derived from advanced laboratory tests; however, capturing the spatial variation in these properties across large quay walls can prove inefficient and costly. Moreover, the difficulty in performing full-scale load tests or small-scale physical models complicates the validation of the numerical model. This paper addresses these challenges by
using monitoring data during the construction of a deep-sea quay wall in the Port of Rotterdam. The quay wall, installed primarily in sand, consists of an anchored retaining wall with a concrete relieving platform. During dredging in front of the wall, fiber optic sensors and inclinometers measured large changes in anchor forces and wall deflection. These changes were then compared to the predictions of a finite element model with the hardening soil model with small strain stiffness constitutive model, with the input parameters derived from cone penetration tests (CPT). The results from the CPT-based numerical model were in good agreement with the measured data, demonstrating the feasibility of integrating numerical modelling and field monitoring while supporting the use of the CPT to calibrate advanced soil constitutive models. The validated model provides a reliable basis against which hypothetical adaptation or remediation measures to the wall can be assessed, such as changes in the dredged seabed depth and surcharge loading.

The majority of the offshore wind turbines constructed to date are founded on monopile foundations. As monopiles’ diameters have increased to 10m and above, there is an increasing concern over the impact of noise generated by using impact hammers. There are several innovative concepts for pile installation which result in reduced noise and vibrations. A number of these concepts include conventional vibratory hammers to overcome the soil resistance and allow installation to the design depth. A driveability assessment is required to provide the correct specification for vibratory hammers. An essential component of a driveability model is to estimate the static resistance to driving (SRD). SRD is analogous to the axial capacity of a pile during driving. It represents the cumulative increase in the shaft capacity associated with further pile penetration and also encompasses a base resistance that is associated with each driving increment. In this paper, a number of published cases of vibro installations are compiled and compared to predictions using commercial software GRLWEAP implemented with a number of SRD models. The pile diameters consider a range from 4.0m to 6.5m and include piles installed in the Dutch sector of the North Sea, where a number of offshore wind farms are currently under construction. Our study assesses the predictive capability of these models and shows that the soil resistance is sensitive to the penetration speed of the pile.

To reduce noise and minimize fatigue damage during pile driving, a new installation method has been developed that differs from conventional pile driving with high-frequency impact blows. This method prolongs the hammer blow, causing a slower pressing force. As a result, it reduces stress waves and imposes a quasi-static loading process on the pile. Consequently, this approach may induce different soil response phenomena compared to conventional pile driving. For instance, friction fatigue is a well-known phenomenon whereby the shaft resistance during installation is affected by cyclic loading and geometrical effects. With this in mind, this paper presents field tests on a pile installed with this new piling method in the port of Rotterdam. Using this field test data, this research will explore the differences in soil response between the prolonged-blow installation technique and conventional driving methods, focusing on friction fatigue.

Extensive research has focused on quantifying the loading behaviour of 1g (g, gravitational acceleration rate) installed open-ended piles using centrifuges. However, the influence of installation stress level on loading behaviour is often ignored, with ramifications for the accuracy and validity of results. In this paper, a loading apparatus is developed to allow in-flight jacking of piles followed directly by vertical or lateral loading, without needing to stop the centrifuge, which facilitates maintaining the installation-related stress state. Model piles are installed at 50g and 1g, and the vertical and lateral responses are analyzed. The effect of pile installation stress level on the initial stiffness, resistance, and soil plug behaviour, is investigated. Results indicate that installation stress level has a more significant and non-uniform effect on pile vertical behaviour than lateral behaviour. Piles that are not fully installed at 50g can mobilize the same vertical resistance as those fully installed at 50g, provided they experience a minimum of 2D (D, pile diameter) in-flight installation length. The arching effect caused by soil plugging, and the denser sand state surrounding the pile toe, may provide higher vertical and lateral resistance for piles installed at 50g compared to those installed at 1g.

Suction piles, also known as suction caissons or suction anchors, have been used extensively in the offshore industry since the 1980s. Existing design methods, such as the DNV-GL method, were primarily developed from installations in dense sands or clays. However, with the continued growth in offshore wind energy, suction piles are being installed more and more in intermediate soils, such as silt, sand and clay mixtures. However, problems can arise when using current design methods for forecasting installation response in these soils. Furthermore, it’s also challenging to classify the soil based on CPT measurements, as well as selecting the appropriate design factors for the suction pile’s shaft and base resistance. To evaluate how design methods perform in intermediate soils, a database has been compiled of installation records across 126 piles at three different sites. This paper focuses on the suction installation phase, comparing the performance of different design methods and soil classification methods in predicting the required suction pressures. The performance of three different design methods have been compared, in addition to a sensitivity analysis on the design factors—indicating the likely range of these factors for intermediate soils.

The rapid expansion of the offshore wind industry into regions with complex geomaterials, such as glauconite sands, presents significant geotechnical challenges. Glauconite sands, commonly found in shallow marine environments, are characterized by their susceptibility to particle crushing and complex shearing behavior, which can lead to high soil resistance and pile driving refusal during monopile (MP) installation. Current drivability prediction models often fail to account for these unique behaviors, leading to uncertainties and inefficiencies in offshore wind farm planning and construction. This research initiative, led by Deltares, seeks to address these challenges through a comprehensive 3-year program combining advanced experimental and numerical modeling. The project involves soil characterization via laboratory tests, calibration chamber testing, and Cone Penetration Test (CPT) simulations. The development of constitutive and drivability models tailored for glauconite sands aims to improve MP installation predictability and optimize offshore operations. The research will also establish soil classification guidelines for glauconite deposits, addressing gaps in current practices. The project’s findings are expected to provide actionable insights for both the scientific and industrial communities, enhancing the design and installation of offshore monopiles (MPs) in glauconite-bearing soils.

As offshore pile foundations increase in diameter and weight, the risk of uncontrolled and unsafe penetration events (pile run) also increases. Traditional approaches to evaluating this risk rely on static resistance to driving (SRD) formulations, equating the SRD to the effective weight of the pile. However, high penetration speeds during uncontrolled pile penetration can lead to a soil response much different to static conditions, particularly with regards to pore pressure dissipation around the pile. With this in mind, the paper proposes an analytical model for determining when uncontrolled penetration may occur and its extent. The model integrates novel SRD formulations with a penetration rate effect model, both of which are derived from cone penetration test (CPT) measurements. The model's predictions were then benchmarked against industry-standard methods using a database of self-weight penetration events in clays and sands of varying densities and strengths. The predicted self-weight penetrations compared well with field observations across the full range of soil conditions and gave a better performance compared to standard prediction methods. Furthermore, the results emphasise the critical role of soil volumetric behaviour during shearing and future research should clarify the influence of rapid penetration on the pile's shaft and base resistance.

As the offshore energy industry begins to develop wind farms in areas of deeper water, the use of traditional foundations such as shallow foundation and driven hollow steel tube piles becomes uneconomical. The deployment of floating turbines and continued development of novel/efficient anchoring systems for these structures will be an important factor in the continued growth of the sector. This paper presents an investigation carried out as part of a proof-of-concept for a novel “bi-wing anchor”. This design will allow a plate anchor to be dropped through the water column and then penetrate the seabed under its own weight. The anchor will then be dragged causing it to embed further into the seabed and provide a greater holding capacity. This paper focuses on experimental as well as analysis of the drag embedment behaviour during the installation and pullout phases. The physical modelling investigations were carried out in a transparent clay-surrogate which enabled observation of the anchor’s orientation during installation. The predictions using analytical modelling showed good agreement with the observed behaviour at varying embedment ratios.

Due to the rapid expansion of the offshore wind industry, wind farms are being developed in areas where glauconite soils are encountered. Of particular interest for the development of windfarms in regions dominated by glauconite sand deposits is the risk associated with the presence of this geomaterial. It is acknowledged that glauconitic soils pose significant challenges during pile installation due to their high susceptibility to particle crushing at relatively low stress levels. This transforms the sand into a low-permeable fine-grained clay-like material, leading to a complex response upon shearing as a result of the change in soil behaviour. In this study, the geotechnical behaviour of a glauconite sand from the Antwerp region in Belgium is investigated by means of a laboratory testing program comprising of index classification tests, compression, direct shear and interface shear strength tests. The laboratory test data are interpreted to improve understanding of the geotechnical properties of this peculiar geomaterial and evaluate its potential implications during pile driving.

The InPAD project investigated the axial capacity of different pile types in sand, including driven precast piles, screw displacement piles and driven cast-in-situ piles. This was done through several full-scale field tests and small-scale physical models, using state-of-the-art instrumentation to analyse the base and shaft response of each pile. This article shows some of the findings from the project and puts forward recommendations for the NEN 9997-1 pile design method.

To mitigate against scour hole formation, scour protection can be placed around offshore wind turbine monopiles. Few studies have considered the beneficial effect of this geotechnical reinforcement measure on the foundation lateral resistance. The contribution of scour protection to lateral resistance of monopiles in sand is investigated in this paper using centrifuge tests and finite element analyses. Multiple scour protection widths and thicknesses are modelled around a monopile, to identify the most effective scour protection properties at mitigating lateral displacements. Two methods for modelling scour protection effects (one using material, the other using direct overburden pressure) are compared. The lateral response of monopiles with different slenderness ratios under various scour protection widths and overburden pressures are simulated. Results suggest that pile lateral displacements reduce by up to 41% when scour protection with width 2D (D, pile diameter) and applied overburden pressure of 30 kPa is used, compared to no scour protection, for a given test case. A method to modify design approaches to consider the beneficial contribution of scour protection on pile lateral behaviour using an envelope diagram is proposed, which provides relationships for scour protection properties and various monopile slenderness ratios.

In this study, driving records of 18 open-ended steel tubular piles installed in dense sandy soil conditions at five sites in the Netherlands were utilized to evaluate models that are currently used in practice for predicting the static soil resistance during driving (SRD), as well as a recently developed method, known as the Unified Method. Since the Unified Method is a static axial capacity-CPT-based design method, slight modifications to the originally proposed formulas were examined to allow estimation of the SRD. This paper presents a modified format of the Unified Method and its performance is assessed by comparing predicted with measured hammer blow count profiles. It is eventually shown that the modified Unified Method leads to overall improved blow count predictions compared to current approaches.

Amsterdam is renowned for its picturesque canals, lined by tall, narrow buildings on either side. Hundreds of kilometres of quay walls support these canals, all founded on long, slender timber piles. Yet many of these quay walls are falling into disrepair and the remaining lifespan of these quay walls is often unknown. Consequently, an extensive amount of research and pilot projects are ongoing, investigating how these walls can be upgraded without intruding on the urban environment. Press-in piling presents an excellent alternative to conventional piling techniques because of its effectiveness in tight working spaces, generating low noise and vibrations as it does so. However, Amsterdam poses some unique geotechnical challenges. Built on marshland, soft clay and peat deposits are widespread throughout. Underlying these deposits are dense sands, the primary load-bearing layer for piled foundations. Understanding how piles behave in these sands is therefore vital, particularly in the case of piles with low embedment depths or in areas where there are thin weak zones in the vicinity of the pile tip. With the growth of press-in piling in the Netherlands, this paper presents some of the opportunities and challenges facing press-in piling, with a particular focus on how the Cone Penetration Test can be used to improve pile design and installation forecasting.

Scour leads to the loss of soil around monopile foundations for offshore wind turbines, which affects their structural safety. In this paper, the effect of scour on the lateral behaviour of monopiles was extensively investigated using finite element analysis, and calibration and comparison were undertaken using centrifuge tests. Piles with three slenderness ratios, i.e., 3, 5 and 8, were studied by keeping the diameter constant and varying the embedment length. Three scour types (local narrow, local wide and global) and four scour depths (0.5D, 1D, 1.5D and 2D; D signifies the pile diameter) were considered in this investigation. The results indicate that the lateral resistance of the pile is the greatest in the case of local narrow scour, followed by that in the cases of local wide scour and global scour. When the scour depth is larger than 1D, the influence of the scour type on the pile lateral bearing behaviour is insignificant. The influence of the scour type and scour depth on the pile lateral bearing behaviour is broadly similar for piles with slenderness ratios of 3, 5 and 8. However, the piles featured with smaller embedment lengths show a larger decrease rate in their lateral capacity, which means the effect of scour should cause more concern on small slenderness ratio monopiles.