Monopiles are the most common Offshore Wind Turbine (OWT) foundations due to their simplicity in design, fabrication, and installation. However, large new-generation turbines have led to significant changes in monopile dimensions, necessitating extensive finite element analyses and ground investigations to meet design requirements. While Cone Penetration Test (CPT)-based p-y methods can analyse slender pile lateral behaviour, they often miss additional resistance mechanisms relevant to rigid monopiles. This paper introduces CPT-informed resistance mechanisms for monopiles to incorporate additional lateral resistances beyond p-y modelling capabilities. Distributed moment–rotation (m-θ) springs are defined by repurposing CPT-based axial capacity estimation methods for piles; and pile tip shear and moment springs are informed by approximating a residual bearing stress post-installation using local CPT q_c values. The performance of the multi-spring model is appraised against data reported from monotonic pile pushover tests conducted at two sand sites. Results show that the multi-spring model is capable of predicting pile head deflections reasonably well within serviceability deflection limits against the reported test data, but ultimate failure loads cannot be predicted using the proposed model. A clear sensitivity in pile response to local variations in CPT q_c is demonstrated.

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Currently, the offshore renewables industry uses a range of foundation systems originally developed for the oil and gas sector. However, innovative foundation measures still need to be developed for offshore renewables because of key differences in scale, loading conditions and the geographical areas in which renewable developments are deployed. Furthermore, the large-scale of offshore wind developments means there is often significant uncertainty regarding the ground conditions between site investigation points. With this in mind, this paper explores the potential use of press-in pile technology for offshore renewable development. Firstly the paper looks at how press-in piling data can be used to inform and ground-truth soil models during pile installation, as well as informing the in-service behaviour of a structure. The paper then describes a number of innovations that may allow for reduced costs and environmental impacts of offshore foundations.@en

Regional-scale assessment of the damage caused by earthquakes to structures is crucial for post-disaster management. While remote sensing techniques can be of great help for a quick post-event structural assessment of large areas, currently available methods are limited to the detection of severely-damaged buildings. Furthermore, remote sensing-based assessment methods typically provide only qualitative results, as they lack integration with information on the building's behaviour in response to seismic-induced ground shaking. In this study, we developed a new methodology that uses airborne Light Detection And Ranging (LiDAR) data in combination with structural indicators of building response to provide a quantitative assessment of earthquake-induced damage at a regional scale. LiDAR datasets collected before and after an earthquake are used to measure residual displacements of building roofs. The resulting lateral drift estimations are used to quantify the level of damage for a specific building typology. Application to the LiDAR datasets collected before and after the 2014 earthquake in Napa Valley, California, demonstrates the capability of the proposed method to detect moderate levels of structural damage, proving its potential for faster and more accurate support to post-disaster management.

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Levees are particularly susceptible to damage during seismic events, and failure mechanisms can involve large deformations due to soil liquefaction within and below the levee. To assess the liquefaction potential below the levees, and for the purpose of planning liquefaction mitigation measures, in-situ and/or laboratory investigations must be carried out. This is a challenge, especially due to the great length of the levees, and the limited financial and time resources available for carrying out the investigations. This paper provides an insight into two examples of investigation work carried out to determine the liquefaction potential and gives an overview of the design measures to remediate the underlying soil. These are the Pušćine levee in Međimurje County, which was reconstructed due to insufficient height in terms of flooding, and the Hrastelnica levee in Sisak-Moslavina County, which was damaged in the 2020 Petrinja earthquake. While numerous dynamic penetration tests were carried out on the Pušćine levee to assess the liquefaction potential, Hrastelnica levee assessments relied on the static (cone) penetration tests. The paper further discusses step forward in mapping the spatial variability of liquefaction potential under the levees, through the efforts of ongoing LeveeLiq project.@en

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.@en

Accurate determination of the load-penetration behaviour of spudcan footings is vital in predicting the performance of offshore structures. Often, insufficient site investigation data is a limiting factor in assessing spudcan penetration, with the selection of suitable parameters typically derived from triaxial tests or Cone Penetrometer Test (CPT) data. A method is presented for simulating spudcan insertion in loose to medium-dense sand, based on minimal data, whereby the CPT tip resistance is used in combination with known correlations of soil properties, allowing for back analysis of CPT profiles through Large Deformation Finite Element (LDFE) simulation. The use of LDFE allows for failure mechanisms to be determined a priori, as a result of the simulation process, while a range of constitutive models can be implemented as necessary. Friction angle, dilation angle and relative density correlations are combined with a calibration of the elastic modulus, used to develop numerical models based on a set of soil sub-layers, each 1 m in depth. The resulting soil characterisations were used to calculate the load-penetration behaviour of several spudcan geometries (which deviate from conventional spudcan shapes) using the LDFE, to assess their performance. Results generated using the proposed technique show strong agreement with a presented field observations.

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Europe’s historic masonry arch bridges are culturally and economically significant, but their long-term safety must be ensured. Scour effects are the most common cause of collapse, so it is necessary to carry out structural assessments to mitigate the risk and prevent potential failures. In this study, a metamodel-based method was used to determine the probability of failure of an existing stone arch bridge in Portugal due to local and contraction scour on the abutments. Non-linear finite element analysis supported the calculation of the reliability index, which took into account the soil-structure interaction and the failure mechanism. The variables with the greatest influence on the load-carrying capacity of the structure were identified and a surrogate model was implemented. Fragility curves were then derived based on the surrogate model, using scour depth as a measure of intensity and load factor as an engineering requirement parameter. The results of the study indicate that the load capacity of the numerical model is compromised when the scour depth of 1.5 m reaches the base of the foundation. As a result, stability problems and settlements are observed in the model. At a depth of 2.5 m, the soil reaches its ultimate bearing capacity.

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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.@en

Three driven precast, four driven cast-in-situ, and four screw injection piles were installed and tested in dense to very dense sand at a site in the Netherlands. Each pile was instrumented with two types of fiber optic sensors and tested under axial compression. Through these tests, a comparison could be made of how different installation methods influence the pile base and shaft response. For example, large residual base stresses were measured in the driven precast piles after installation. Of the three pile types tested, the driven precast piles also reached the highest base stresses, mobilizing their full base resistance at comparatively low displacements. The base response of the driven cast-in-situ piles was also like that of a driven precast pile with residual stresses excluded. In contrast, the screw injection piles mobilized much lower ultimate base resistances and with a much lower stiffness. In terms of shaft resistance, the precast piles showed friction fatigue effects in line with existing models, but this effect was not evident for the driven cast-in-situ or screw injection piles. Finally, shaft and base resistances measured in the dense to very dense sand layers were greater than limiting resistances prescribed in several design standards. By taking this into consideration in design standards, the results would help reduce some of the overconservatism present in design and consequently reduce the financial and environmental cost of pile manufacturing and installation.@en

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.@en

The European offshore wind sector has grown rapidly, with significant advances in turbine technologies, in creased sizes, and construction locations further from the shore in deeper waters than ever before. A critical challenge has emerged relating to a growing lack of knowledge surrounding how to design foundations to support these new turbines, with the safety, life-span, cost, and environmental implications coming increasingly into question. To maintain Europe’s stance as a World-leader in offshore wind, Foundations for Offshore Wind Turbines (FRONTIErS) Doctoral Network has been designed to bring together research-intensive universities and major industry stakeholders to train the next generation of graduates with the appropriate skills to tackle the emerging issues presenting as a barrier to continued development of the sector. Eleven Doctoral Candidates have been recruited to tackle significant challenges related to foundation design and performance. Projects focus on topics such as: understanding soil variability, effect of cyclic loading on axial capacity, pile aging, dynamic modelling informed from in-situ testing, time and spatial variation in soil properties, driveability modelling, gravity-base scour effects, multi-directional loading effects, centrifuge testing of cyclic loading response, and dynamic features of wind turbine foundations. This paper presents a preliminary overview of the various PhD projects ongoing as part of this network, which are in the early stages, as well as a summary of training conducted to date. @en

Extensive studies have been performed on the effectiveness of scour protection against scour erosion progression. But there is little research to date evaluating the effect of scour protection on vertical resistance behaviour of monopile foundations. This paper investigates the influence of scour protection on the vertical loading behaviour of monopiles installed in sand using centrifuge tests and finite element analysis (FEA). Four scour protection widths (1D, 2D, 3D, 4D; where D is the pile diameter) and three scour protection thicknesses (1 m, 2 m, 3 m) were modelled on a pile with a slenderness ratio (L/D) of five. In the FEA, the scour protection mechanism was modelled using two strategies, namely the ‘stress method’ by applying stress and the ‘material method’ by applying virtual material on the seabed surface around the pile. Outcomes between these two strategies were compared, and the contact coefficient δ used in the ‘material method’ for describing the contact effectiveness of the overlaying scour protection material with the pile structure was introduced, providing a more scientific and accurate calculation reference for engineering applications. The results indicated that the vertical capacity of monopiles could be increased by 5% to 23% by adopting the scour protection measure, depending on the scour protection width and scour protection thickness.@en

Full-scale axial load tests were performed on five screw injection piles founded in medium-dense to dense sand at a site in Delft, the Netherlands. Each pile was instrumented with distributed fiber-optic sensors along its full length, giving detailed insights into the shaft and base response under compression loading. The paper focuses on the pile base response and combines the test results with a newly compiled database of instrumented load tests on screw displacement piles in sand. Given the range of screw displacement piles on the market, the influence of different installation methods and pile geometries on the base resistance can be assessed through the database. In summary, the analysis showed that all screw displacement pile types tended to mobilize base capacities similar to bored or nondisplacement piles. Despite high variability in the database, no significant trend with pile geometry, such as length or diameter, was evident.

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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.

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Since most of the existing port infrastructure needs to be upgraded or replaced in the coming decades, the Port of Rotterdam Authority invests in sustainable and future proof design solutions. Together with their partners, they aim to reduce the port’s CO₂ emissions by 50% in 2030 and intend to achieve a zero carbon footprint by 2050. The effective use of new and existing materials is crucial to reach these goals. However, the actual capacity of port infrastructure is generally not precisely known, given that no failures have been observed in practice and the existing berthing facilities are performing very well. In order to derive insight into the reserve capacity of these structures, unique full-scale field tests have been conducted on flexible dolphins, foundation piles and anchor piles. This paper presents the technical, commercial and environmental results of recent pile load tests performed in the port of Rotterdam. The tests have led to a significant reduction of CO2 emissions associated with manufacturing and installing foundations, as well as reducing installation risks. Furthermore, a higher reliability level was obtained using less materials. This paper shows that in spite of the cost of performing full-scale field tests, the verification of the actual capacity of foundation piles is crucial to improve the carbon footprint of port infrastructure.
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Geotechnical structures are often partially embedded, if not fully embedded, making it challenging to assess the remaining lifetime and reusability of a foundation. In-situ monitoring offers a solution. By attaching different types of sensors to a foundation, the foundation’s response and reliability can be assessed at various stages of a structure’s life cycle. To illustrate this, an example of a “smart quay wall” is taken from the Port of Rotterdam. During the design phase, fully instrumented pile tests showed that the design could be optimised, leading to substantial financial and carbon emission savings. During construction, movements and forces in the quay wall were closely monitored and were used to validate a numerical model, thus providing a reliable tool at later stages during the quay wall’s lifetime when reuse or readaptation of the quay wall is being considered. Lastly, ongoing measurements during the operational phase of the quay wall have shown a large amount of residual capacity, particularly when compared to the pile load tests.@en

Offshore jack-up rigs are most commonly founded on large-diameter conical “spudcan” foundations, which are frequently designed using traditional analytical methods for shallow footings. This paper presents the design of a spudcan installed off the coast of Tunisia. The maximum penetration depth of the footing under the available preload is predicted by a combination of analytical techniques, 2-dimensional axisymmetric modelling and 3-dimensional Finite Element Methods (FEM) using large strain arbitrary Lagrangian-Eulerian (ALE) techniques. Spudcan penetration based on FEM simulation of CPT soil profiles forms the basis of a comparison with results from the Society of Naval Architects and Marine Engineers (SNAME) guidelines. Particular attention is given to model calibration using the limited site investigation data available. Results are presented for the effect of penetrating footings on the behaviour of neighbouring footings, showing good agreement with conventional prediction methods.

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The paper presents a risk assessment model, developed in the project oVERFLOw and further implemented in the project CROSScade, for determining the direct and indirect impacts of flooding hazards. As a consequence of flooding, transport infrastructure and flood protection systems can be significantly damaged and cause cascading effects on other infrastructure. To achieve flood resilient infrastructure, it is necessary to assess the vulnerability of critical assets in the affected area. The model uses novel vulnerability assessment methods for embankments and bridges exposed to different flood hazard scenarios allowing the asset owners to understand risk and performance of their infrastructure. Scarce financial resources are allocated on the critical assets allowing significant cost savings and avoiding the waste of non-renewable resources in strengthening large sections which have sufficient resilience. The consequence analysis is based on an improved quantification model for direct and indirect impacts of different flood hazard scenarios used for risk mapping of the affected area.@en

One of the ways to install plate anchors in deep seabed is to drop the anchor system from the sea level and allow it to initially embed in the seabed under its own weight. Further dragging would cause the anchor to rotate and embed further into the seabed. There could be difficulties of getting the anchor plate horizontal or mooring line to be perpendicular to the plate where the maximum pullout capacity could be achieved. As part of the investigations, various aspects of the plate performance were examined through centrifuge testing in which the plate orientation and pullout angles were varied. It was presumed that dynamic stability of the anchor (during field installation) can be achieved by having the plate in biwing configuration. Therefore, the performance of the biwing anchors having different spacing between the plates was also examined in the centrifuge testing program and the findings were compared with predictions obtained through finite-element modeling (FEM). Both pullout directions and the plate angles considerably influenced the pullout capacity factors. The comparison between the predicted pullout capacity using FEM and measured pullout capacity for biwing anchors at shallow embedment depths was excellent. However, the FEM-predicted pullout capacity was noticeably lower than the measured ones for deep anchors. Pullout capacity of biwing anchors at shallow embedment depth increased as the spacing between the plates S increased from 0 to 0.5B. However, there appears to be a slight reduction in the performance in deep embedment anchors. This is also reflected in FEM findings.

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Earthquakes are natural hazards leading to the greatest human and economic losses, which are mostly due to structural collapses. Rapid identification and assessment of earthquake-induced damage to structures is therefore an essential component of the emergency response, and instrumental to effective reconstruction plans. Typically, structural damage assessment is conducted through building-by-building inspections during post-earthquake field reconnaissance missions. These missions are expensive and time-consuming, especially if large areas need to be investigated. Remote sensing techniques provide a relatively low-cost, wide-area alternative to in-situ monitoring. Classification and change detection based on pre- and post-event optical and synthetic aperture radar (SAR) satellite images are the most used approaches to detect damaged structures after earthquakes. However, these techniques only provide qualitative observations of collapsed or severely damaged structures. In this work, we present a new approach for the quantitative assessment of earthquake-induced structural damage based on displacement measurements acquired by Airborne Light Detection And Ranging (LiDAR). The approach is based on the integration between LiDAR-based observations and structural indicators of damage. The application to the analysis of 684 buildings affected by the 2014 Napa earthquake, in California, demonstrates a good agreement between the LiDAR-based results and independent in-situ observations. This work sets the basis for the innovative exploitation of remote sensing data in disaster management. @en