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

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

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

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

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

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

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

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

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

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

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

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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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Cone penetration tests (CPTs) can quantitatively inform about the mechanical state of a sand. However, relating measured cone resistance values to sand state requires complex back-analysis of the processes occurring in the soil during the test. This paper provides new evidence of the value added in this area by modern large-deformation modelling based on the material point method (MPM). It is shown that accurate simulation of the relationship between cone resistance and sand state can be achieved, on condition that the constitutive behaviour of the soil - and especially its critical state features - is adequately modelled over a wide range of confining pressures. This study relies on the predictive capabilities of the critical state NorSand model, and shows how previous calibrations endeavours from the literature (based on triaxial test results) can support the MPM simulation of unrelated CPT results obtained through calibration chamber tests. MPM CPT simulations of ever-increasing quality will positively impact the state of the art of CPT interpretation procedures, to date still largely based on simplified cavity expansion theories.

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

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Submarine buried pipelines are often laid in trenches backfilled with loose sandy soil, which is intrinsically prone to liquefaction. When liquefaction is triggered, the soil tends to behave as a viscous fluid with vanishing shear strength and very limited ability to restrain structural displacement, for instance during the occurrence of pipeline flotation. Recently, a 2D CFD-based approach for the analysis of pipe flotation in liquefied sand has been proposed by Pisano et al. (2020), in which soil reconsolidation effects are phenomenologically captured by considering rheological parameters that evolve in space and time as pore water pressures dissipate. Despite a remarkable agreement with experimental data from the literature, the complexity and computational costs of such approach may still hinder its applicability to pipeline engineering practice. To overcome this limitation, a simplified model is proposed herein, in which all the forces governing the motion of the pipe are expressed via simple analytical relationships. After thorough validation against 2D CFD results and relevant experimental data, it is concluded that the new simplified model largely retains the predictive capability of Pisano et al.’s framework in combination with negligible computational costs.@en

The Material Point Method (MPM) has been gaining increasing popularity as an appropriate approach to the solution of coupled hydro-mechanical problems involving large deformations. This study extends the implicit GIMP-patch method for coupled poroelastic problems recently proposed by Zheng et al. (2021b) to tackle large-deformation problems in (nearly) isochoric elastoplastic geomaterials, particularly by remedying the numerical inaccuracies caused by volumetric locking, such as spurious stress oscillations and an excessively stiff overall response of the system at hand. To overcome these difficulties in two-phase coupled analyses, the B¯ approach of Hughes (1980) is incorporated into an existing version of the implicit GIMP-patch method. Details regarding the formulation and implementation of the proposed method are provided, while several benchmark problems are numerically analysed to evaluate its performance in the presence of elastoplastic behaviour. Particular emphasis is placed on (i) mitigating effective stress oscillations and (ii) solving several two-phase, coupled, large deformation geotechnical problems. The numerical results confirm the suitability of the implicit B¯ GIMP-patch method for the solution of geotechnical problems spanning weak to strong hydro-mechanical coupling and small to large deformations.

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The analysis of cyclically loaded piles is acquiring ever greater relevance in the field of geotechnical engineering, most recently in relation to the design of offshore monopiles. In this area, predicting the gradual accumulation of pile deflection under prolonged cycling is key to performing relevant serviceability assessments, for which simplified pile–soil interaction models that can be calibrated against common geotechnical data are strongly needed. This study proposes a new cyclic p−y model for piles in sand that takes a step further towards meeting the mentioned requirements. The model is formulated in the framework of memory-enhanced bounding surface plasticity, and extends to cyclic loading conditions the previous monotonic, CPT-based p−y formulation by Suryasentana and Lehane (2016); additionally, detailed modelling of pile–soil gapping is introduced to cope with the presence of unsaturated sand layers or, more generally, of cohesive soil behaviour. After detailed description of all model capabilities, field data from an onshore cyclic pile loading test are simulated using the proposed p−y model, with the most relevant parameters calibrated against available CPT data. Satisfactory agreement is shown between experimental and numerical results, which supports the practical applicability of the model and the need for further studies on a fully CPT-based calibration.@en

This study presents the formulation and implementation of a fully implicit stabilised Material Point Method (MPM) for dynamic problems in two-phase porous media. In particular, the proposed method is built on a three-field formulation of the governing conservation laws, which uses solid displacement, pore pressure and fluid displacement as primary variables (u–p–U formulation). Stress oscillations associated with grid-crossing and pore pressure instabilities near the undrained/incompressible limit are mitigated by implementing enhanced shape functions according to the Generalised Interpolation Material Point (GIMP) method, as well as a patch recovery of pore pressures – from background nodes to material points – based on the same Moving Least Square Approximation (MLSA) approach investigated by Zheng et al. [1]. The accuracy and computational convenience of the proposed method are discussed with reference to several poroelastic verification examples, spanning different regimes of material deformation (small versus large) and dynamic motion (slow versus fast). The computational performance of the proposed method in combination with the PARDISO solver for the discrete linear system is also compared to explicit MPM modelling [1] in terms of accuracy, convergence rate, and computation time.

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