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.

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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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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).

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Many flood protection dams in Europe were built more than 100 years ago. These dams often do not meet 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 an idealized cross-section of a flood protection dam has been carried out in the geotechnical centrifuge at TU Delft in order to study the seepage behaviour of a horizontally layered dam consisting of layers with coarse and fine-grained material. Main aspects of the testing equipment such as a specially manufactured test box which allows to simulate certain flood events of different durations and intensities are presented. Furthermore, measured values of the pore pressure during the investigated flood event, are presented and discussed in comparison to the results of finite element modelling of the dam. Finally, the influence of the hydraulic boundary conditions on the seepage behaviour in the physical and numerical modelling is critically discussed.@en

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.

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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.

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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.

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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.

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Fuelled by technological innovations and the growing commitment of countries to reduce their carbon footprint, offshore wind has steadily been gaining ground on non-sustainable sources of energy. According to the International Energy Agency (IEA) [2], it is foreseen that wind will be the principal source of energy in Europe by 2027. However, in an effort to protect the marine environment from sound pollution [1], regulations applicable to offshore wind endeavors have become more stringent. To sustain the growth of the offshore wind sector, more durable installation methods are required. Prolongation of the impact duration has been identified as a suitable method to protect the marine environment from sound pollution [7]. However, the market introduction of this technology is hampered by a lack of understanding of its effects on soil-structure interaction. Therefore, concerns exist on (mono)pile drivability, as well as the performance of the foundation under axial and lateral loads. To address this issue, a series of centrifuge experiments is performed in the centrifuge facility of Delft University of Technology (DUT). The experiments are conducted at 50g acceleration and show the effect of blow prolongation on the drivability of miniature steel, tubular pile (outer diameter, D = 42 mm; wall thickness, t = 2 mm) in dry GEBA sand at 80% relative density. The blow-prolongation technology that is assessed is IQIP’s BLUE Piling (BP) Technology [4]. Details on the actuator used to simulate BP technology in the centrifuge are provided by the work of Quinten et al. (2022) [6]. Prior to dynamic installation, the pile was allowed to settle in into the sample under 1g conditions. Subsequently, an second self-weight penetration phase is initiated by increasing the centrifuge acceleration to 50g, while the ram acts as dead-weight on top of the pile. Following the self-weight penetration phase, the centrifuge is intermittently stopped and reinitiated to (re)set the actuator. The BP ram has a mass of 1.889 kg ram and stroke of 40 mm. The results of the BP experiment are compared against those from centrifuge experiments involving impact hammering (IH), the most widespread method of installation for monopiles in the offshore sector. A detailed description of the actuator, the miniature impact hammer of DUT, is provided by Quinten et al. (2022) [5]. The model pile was pre-embedded at a depth of 50 mm under 1g conditions prior to the dynamic installation phase. The hammer operates at a driving frequency of 10 Hz and is equipped with a ram of 0.140 kg, which is released from a height of 40 mm. Comparison of the results of both experiments, reveals striking differences in the cumulative settlement behavior of the pile as well as the pile stresses. The cumulative pile displacement charts, as shown in Figure 1, show significant differences between the two installation methods. For BP (Figure 1a), a series of 3 single blow experiments was conducted. For IH (Figure 1b), the experiment lasted for a total of 37 consecutive blows. The realized pile set during the experiment is comparable between the two tests. The average normalized displacement equates to 0.5D and 0.03D per blow for BP and IH respectively. The soil level inside the pile cavity was measured following the execution of both experiments. The associated measurements indicated that both piles were driven in a fully coring mode. When considering the prototype pile dimensions and soil conditions, this finding corresponds well with the work of Jardine et al. (2005) [3]. Further differences between IH and BP were observed in terms of (peak) pile stress. The driving forces are reduced from 25 kN for IH to 6 kN for BP, respectively. The driving factor behind this reduction is the decrease in interface stiffness between the ram and the anvil. The latter completely offsets the effects associated with the use of a significantly heavier ram mass in the case of BLUE Piling. When the driving forces are expressed as a percentage of the pile yield limit, aforementioned figures respectively equate to 42% and 10%. Extrapolated over the full installation sequence, the latter would contribute to a reduction in the fatigue accumulated during installation.

The results presented here form the first step towards understanding the effect of blow duration soil-structure interaction for blow prolongation technology. For the set of installation parameters and boundary conditions considered in this study, it is shown that the differences in pile installation behavior can be captured using centrifuge modeling. The prolongation of blow duration results in a significantly different overall installation behavior. When looking at the driving forces, the decrease of the interface stiffness between the ram and anvil produces the anticipated decrease in peak driving force. A sustained physical modeling effort is required to ultimately lay the basis for a predictive installation framework for blow-prolonging technology, which would arguably accelerate its adoption by the industry. The latter should help the reek the associated benefits, particularly in terms of fatigue reduction and sound remediation in the near future.@en

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.

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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.

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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.

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Large areas of the Netherlands are dominated by deep, soft soil deposits, posing a challenge to engineers with respect to the design of axially loaded foundations. The design of these foundations is primarily based on methods which use cone penetration test (CPT) parameters, such as that outlined in the Dutch national standard NEN 9997-1. A recent update to this standard included revised reduction factors for the pile base resistance. However, it is believed that this update is overly conservative in certain design situations, leading to increasing cost, environmental impact and difficulty of installation. As a result, a national research project was initiated to enhance the understanding of pile-soil interaction effects and their influence on pile design methods. As part of this project, a series of large-scale field tests on fully instrumented piles in dense sand has been executed and are being analysed with a view to refining the national standards and contribute to the existing knowledgebase on piles worldwide. This paper shall provide an overview of two pile test sites that have been developed as part of the programme, along with the design of the testing programme and an overview of the results.@en

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.

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The scour protection layers are usually installed around the monopiles to prevent the formation of scour hole. While extensive studies have been performed on the effectiveness of scour protection layer as mitigation measure, no study to date has been found to quantify the influence of scour protection layer on the lateral response of monopiles. In this study, centrifuge tests and numerical analyses were performed to examine explicitly the influence of the scour protection layer on the monopile response under lateral load in sand. It was found that a scour protection layer with a diameter of 5 times the diameter of the monopile (5D) and equivalent surcharge pressure of 15 kPa can increase the foundation lateral capacity by more than 30% and significantly decrease the accumulation of deflection by more than 100% in dense sand. Numerical analyses suggested that the beneficial contribution is attributed to the densification of sand and the increase of effective stress around the pile, which increased the stiffness and ultimate resistance of the soil reaction curve (i.e., p-y curve). Numerical parametric studies suggested that the beneficial effect of scour protection layer is also applicable to monopile in loose sand and by considering the contribution of the scour protection layer, the embedment length of the monopile can be reduced by 10%.

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Monopiles are the most popular foundation for offshore wind turbines. These foundations typically have a low length to diameter ratio and undergo a rigid body rotation when subjected to lateral load. This paper presents results from an extensive numerical investigation involving 3D finite element analyses to demonstrate that the lateral moment-rotation response of a monopile in sand can be represented using a single non-linear rotational spring located at a depth of about 0.75 times the pile embedment. Expressions for the elastic rotational stiffness of a monopile under very low rotations are developed and these combined with observations from measured non-linear variations of rotational stiffness, that are supported by the numerical analyses, are used to develop a simple approximate expression that can be used to determine the response of a monopile to a monotonic lateral load in sand.

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The large-diameter monopiles are the most preferred foundation used in offshore wind farms. However, the influence of pile diameter and aspect ratio on the lateral bearing behavior of monopiles in sand with different relative densities has not been systematically studied. This study presents a series of well-calibrated finite-element (FE) analyses using an advanced state dependent constitutive model. The FE model was first validated against the centrifuge tests on the large-diameter monopiles. Parametric studies were performed on rigid piles with different diameters (D = 4–10 m) and aspect ratios (L/D = 3–7.5) under a wide range of loading heights (e = 5–100 m) in sands with different relative densities (Dr = 40%, 65%, 80%). The API and PISA p-y models were systematically compared and evaluated against the FE simulation results. The numerical results revealed a rigid rotation failure mechanism of the rigid pile, which is independent of pile diameter and aspect ratio. The computed soil pressure coefficient (K = p/Dσ^′ v) of different diameter piles at same rotation is a function of z/L (z is depth) rather than z/D. The force–moment diagrams at different deflections were quantified in sands of different relative density. Based on the observed pile–soil interaction mechanism, a simple design model was proposed to calculate the combined capacity of rigid piles.

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Planning a monitoring campaign for a natural submarine slope prone to static liquefaction is a challenging task due to the sudden nature of flow slides. Therefore, gaining a better insight by monitoring the changes in pore pressure and acceleration of the soil mass, prior to and at the onset of static liquefaction, of submerged model slopes in the laboratory, helps in quantifying the minimum required triggering levels and ultimately the development of effective margins of safety for this specific failure mechanism. This study presents a set of physical model tests of submarine flow slides in the large-scale GeoTank (GT) of Delft University of Technology, in which a tilting mechanism was employed to trigger static liquefaction in loosely packed sand layers. Novel sensors were developed to locally monitor the hydro-mechanical soil responses acting as precursors of the onset of instability. The measurements indicated that soil instability can initiate at overly gentle slope angles (6–10°) and generate significant excess pore water pressures that intensify the deformations to form a flow slide. Moreover, it was observed that the onset of instability and its propagation are highly dependent on the rate of shear stress change and the state of the soil. The obtained data can be used for the future validation of numerical models for submarine flow slides.

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The scaling laws for the centrifuge modelling of the initiation and propagation of static liquefaction in submerged slopes are investigated in this paper. A theoretical model is developed to analytically determine the scaling factor of fluid viscosity in simulating the onset of static liquefaction by detailed analysis of the hydromechanical processes at the grain scale. Based on this, a fluid with a viscosity of N-times that of water (N-fluid) is suggested, where N is the geometrical scaling factor in centrifuge modelling. A fluid with a viscosity of N-times that of water (N-fluid) was adopted for simulating dynamic events in the centrifuge; N-fluid is used and suggested by previous researchers. Centrifuge tests were designed to examine and verify the scaling factors for pore fluid viscosity in simulating the onset of static liquefaction and the post-liquefaction behaviour of subaqueous landslides. These tests were performed at 10g, 30g, and 50g conditions, with N-fluid, N-fluid or water, where g is the Earth’s gravitational acceleration. Results confirm that the correct scaling factors (prototype/model) for pore fluid viscosity are 1/N and 1/N for investigating the onset of static liquefaction and the post-failure behaviour of the submarine slopes, respectively.

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The majority of offshore wind structures are supported on large-diameter, rigid monopile foundations. These piles may be subjected to scour due to the waves and currents that causes a loss of soil support and consequently decreases the pile capacity and system stiffness. The results of numerical models suggest that the shape of the scour hole affects the magnitude of pile capacity loss; however, there is a dearth of experimental test data that quantify this effect. This paper presents a series of centrifuge model tests on an instrumented model pile that investigates the effects of scour-hole geometry on the response of a laterally loaded pile embedded in sand. The pile instrumentation allowed load–displacement and p–y (soil reaction – displacement) curves to be derived. Three scour geometries (global, local wide, and local narrow) and three scour depths (1D, 1.5D, and 2D; where D is pile diameter) were modelled. For all three scour types, pile moment capacity decreased almost linearly with increase of scour depth. Simple empirical relations were proposed to evaluate the detrimental influence of scour on the pile moment capacity. A new method has been developed to allow designers to quantify the effect of scour-hole shape and severity of scour on the pile response.

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