The large-diameter monopile is a commonly used foundation concept for offshore wind turbines. The advantages of geometrical simplicity and reliable performance make it often the most attractive solution. Despite the concept’s high popularity, optimisation of the current design models can still be made. To address fundamental understanding of modelling effects in centrifuge testing of laterally loaded monopiles in sand, a large coordinated centrifuge-testing programme across nine different centrifuge centres worldwide has been conducted. This paper presents firstly the results of a local benchmark modelling of model test series performed in two centrifuges and secondly the results of global benchmark testing across the nine centrifuges. The results highlight the reliability of centrifuge testing as it was possible to model a similar prototype response in both the local and global benchmark tests, despite differences in the experimental setups and pile geometries. Furthermore, as examples of the modelling technique, two different cases are presented, one showing the effect of installation and one showing the effect of pile penetration depth. Finally, recommendations are provided to enhance centrifuge testing of monopile response under complex loading.

Many flood protection levees in Europe were built more than 100 years ago. These levees often do not meet the current flood protection requirements due to increased level of safety requirements, higher damage potential in the valley plains and due to higher peak discharges or water levels expected with changing climatic conditions. A first series of centrifuge tests on two idealized cross-sections of the river Rhine flood protection levee have been carried out in the geotechnical centrifuge at Delft University of Technology in order to study the transient seepage behaviour of a horizontally layered levee consisting of layers with coarse and fine-grained material. Main features and design considerations of a specially manufactured flood simulator for the geotechnical centrifuge which allows replicating scaled flood events with predefined durations and intensities are presented. Furthermore, measured values of the pore pressure during the investigated flood event are reported and discussed in comparison to the results of finite element modelling of the levee. Finally, the potential impacts of the hydraulic boundary conditions on the seepage behaviour in the physical and numerical models of the levee are critically discussed.

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.

The authors present a comprehensive numerical study on the lateral response of pile foundations in sands with a constant relative density. The influence of the pile configuration (length (L) diameter (D) and flexural rigidity), load eccentricity (h), sand type and relative density (Dr) was investigated. This discussion provides some additional insights on the lateral response of large diameter monopiles in uniform sand by combining the authors work with the observations in Wang et al. (2021) and Richards et al. (2021).

A newly developed line-style sand pluviator has been calibrated to prepare repeatable sand specimens of specific statuses of compactness and homogeneity for laboratory tests. Sand is falling via a bottom slot of a fixed hopper, and by moving the sample container under the slot, the container is evenly filled with sand. The pluviator is designed with high flexibility: The falling height of sand, the hopper’s opening width and the relative moving speed between the hopper and the sample box can be easily adjusted. By changing these control factors, sand specimens of a wide range of densities can be prepared. A series of specimen preparation was performed using the coarse Merwede River sand. Performance of the pluviator was systematically evaluated by exploring the alteration of achievable density, as well as checking the homogeneity and fabric of the prepared samples by CT scanning. It was found that the density of prepared coarse sand samples has monotonic correlations with none of the three control factors. Furthermore, CT scanning results suggested that the prepared samples exhibited excellent homogeneity in the horizontal direction but periodical alteration of density in the vertical direction. Based on these calibration test results, a preliminary hypothesis is proposed to describe the general working principles of this type of pluviators a priori, illustrating the mechanisms dominating the non-monotonic correlations between control factors and the relative density as well as the vertically prevalent heterogeneity of specimens. Accordingly, practical recommendations are made in a unified framework in order to lessen the load of similar calibration work.

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.

This paper presents a synthesis of recent and new research conducted by the authors on laterally loaded monopiles in drained sand. The research involved reduced-scale field tests, centrifuge model tests, finite element (FE) simulations and comparisons of design approaches with published experimental data. The influence of the monopile base on lateral response is first discussed by drawing on field tests and numerical simulations and it is shown that the base generally provides a negligible contribution. The applicability of the API p-y formulation is then investigated through systematic FE analyses. The results show that this formulation leads to inaccurate predictions largely due to the assumption of a high initial stiffness varying linearly with depth and an unrealistic hyperbolic tangent back-bone function. Based on new insights into pile-soil interaction together with elastic simulations of laterally loaded rigid piles and new observations based on 26 pile tests, a simple rotational spring model is proposed to allow rapid quantification of the non-linear response of rigid monopiles in uniform sand. The effect of monopile flexibility is then added through a new straightforward correction factor based on 80 extra FE simulations. Finally, an example application of the proposed approach for a typical monopile design is presented.

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 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.

Piles have been widely used as foundations to resist lateral loads. For the design of a laterally loaded pile, one of the most important inputs is the ultimate soil resistance (p_ult = K_ultDσv^′,whereKult is the ultimate lateral soil resistance coefficient, D is the pile diameter, and σv^′ is the vertical effective stress). However, great discrepancy can be found in the existing design equations for piles in sand. To provide new insights and clarify the discrepancy in previous studies, in this study, a series of numerical simulations were performed on piles of different configurations using the finite element model validated by centrifuge pile tests. The computed results suggest that K_ult is a function of depth ratios z/D and z/L for the flexible and rigid piles, respectively (where z is the absolute depth and L is the embedded pile length), and all existing design equations failed to reproduce the magnitude and distribution of K_ult . Additionally, the K_ult of horizontally translated fixed-head rigid piles exhibits the same pattern as that of free-head flexible piles, suggesting that the difference between free-head flexible piles and rigid piles is caused by the change of failure modes.

The influence of combined loading on the response of monopiles used to support offshore wind turbines (OWTs) is investigated in this paper. In current practice, resistance of monopiles to vertical and lateral loading is considered separately. As OWT size has increased, the slenderness ratio (pile length, L, normalised by diameter, D) has decreased and foundations are tending towards intermediate footings with geometries between those of piles and shallow foundations. Whilst load interaction effects are not significant for slender piles, they are critical for shallow footings. Previous research on pile load interaction has resulted in conflicting findings, potentially arising from variations in boundary conditions and pile slenderness. In this study, monotonic lateral load tests were conducted in a geotechnical centrifuge on vertically loaded monopiles in dense sand. Results indicate that for piles with L/D = 5, increasing vertical loading improved pile initial stiffness and lateral capacity. A similar trend was observed for piles with L/D = 3, when vertical loading was below 45% of the pile’s ultimate vertical capacity. For higher vertical loads considered, results tended towards the behaviour observed for shallow footings. Numerical analyses conducted show that changes in mean effective stress are potentially responsible for the observed behaviour.

Due to the environmental crisis, there is a need for a more conscious and integrating design process within the field of urban infrastructure development. Through cooperation between civil engineering and spatial design resilience of the built environment can be increased. Delft University of Technology investigates interdisciplinary design as a method and incorporates this into its MSc-level education of students in the faculties of civil engineering and architecture. The focus of the research was on the reconstruction projects after disasters like hurricanes and tsunamis. By way of surveys of the participating students, the effectiveness of the interdisciplinary design methods used, and the interpretation of the terms multidisciplinary and interdisciplinary are revealed. From survey results about understanding of multidisciplinary and interdisciplinary it can be concluded that interdisciplinary design should entail a conscious and orchestrated process in which the disciplines present their ideas within a shared value system before systematic integration. The challenges are at personal and cognitive levels, an open attitude is necessary to be able to perceive and react, process and understand, retrieve information. Only then decisions on - and production of - appropriate responses come out of co-creation between engineering within the spatial design process.

Early Warning Systems (EWS) are non-structural measures for landslides disaster prevention. They are based on the detection of impending failure signals. The results of a landslide simulation experiment where accelerometers were used to identify pre-failure signals are presented in this paper. Landslide was simulated in a tilting flume filled with sandy soil. During the experiment, the flume was fixed at 30° inclination and water percolated through the soil until it slid. Accelerometers were embedded into the soil and recorded acceleration data from the beginning of the experiment until failure. Acceleration data were analyzed in time domain aiming at estimating translational velocity of the movement. Angular variation was also estimated from acceleration data. The experiment was recorded with a camera and pictures were used for Particle Image Velocimetry (PIV) analysis, in order to validate the estimated translational velocity. Results showed that accelerometers can identify pre-failure signals before any macroscopic movement could indicate impending failure in fast to very fast landslides, showing their potential to be used in EWS. Validation of estimated velocities was not always possible due to PIV setup constraints and the velocity of the mass movement simulated. In fact, the estimated translational velocities seem to be unreliable. On the other hand, the results suggest that acceleration data and angular position variation trend and rate can be incorporated into EWS.