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

The shear strength and compression properties of stiff Boom clay from Belgium at a depth of about 16.5 to 28 m were investigated by means of cone penetration and laboratory testing. The latter consisted of index classification, constant rate of strain, triaxial, direct simple shear and unconfined compression tests. The Boom clay samples exhibited strong swelling tendencies. The suction pressure was measured via different procedures and was compared to the expected in situ stress. The undrained shear strength profile determined from cone penetration tests (CPTs) was not compatible with the triaxial and direct simple shear measurements, which gave significantly lower undrained shear strength values. Micro-computed tomography (μCT) scans of the samples showed the presence of pre-existing discontinuities which may cause inconsistencies in the comparison of the laboratory test results with in situ data. The experimental data gathered in this study provide useful information for analyzing the mechanical behaviour of Boom clay at shallow depths considering that most investigations in the literature have been carried out on deep Boom clay deposits.

Monopiles are the most common foundation for offshore wind turbines (OWTs), accounting for roughly 80% of installations in Europe. Despite advancements in research, critical knowledge gaps remain, especially regarding the behaviour of monopiles under long-term cyclic loading. Addressing these gaps is vital for enhancing the safety and costeffectiveness of future offshore wind farms and for assessing the life-cycle conditions of existing OWTs. The "MIDAS: Monopile Improved Design through Advanced Cyclic Soil Modelling" project, conducted in the Netherlands by TU Delft, Deltares, NGI, and industry partners, aimed to fill these gaps. Focusing on sandy soils, MIDAS employed a comprehensive methodology combining experimental (element and centrifuge testing), numerical, and theoretical modelling. This paper presents the centrifuge modelling component, detailing the design and implementation of the testing program, including cyclic load definitions, model pile instrumentation, loading configurations, model seabed preparation, and test procedures. Findings indicate that monotonic responses of monopiles with different configurations can be normalized effectively, validating the quality of experimental outcomes in the context of established theoretical models. The study also explores the impacts of stress levels, monopile dimensions, and drainage conditions on cyclic behaviour, contributing valuable insights to the understanding of monopile-soil interactions under cyclic loads.

Monopiles are the predominant type of foundation used for offshore wind turbines. The increase in size of monopiles and the stricter environmental regulations in terms of underwater noise levels has motivated the development of alternatives to the conventional impact-driving method of monopile installation. One of the alternatives is the (axial) vibratory installation, which has been previously studied in field [1, 2, 4] and laboratory [3, 5] conditions. However, there is limited knowledge on the effects of vibratory installation (and how these effects differ from those caused by impact-driving) on the lateral response of monopiles. This extended abstract presents the results of an ongoing Join Industry Project (SIMOX – Sustainable Installation of XXL Monopiles) which aims at comparing different installation methods from the point of view of driveability, noise emissions and lateral response. The present abstract particularly focuses on the lateral response of monopiles. As a first step towards the large-scale onshore field tests to be executed in 2023, a laboratory study was conducted at the Water-Soil Flume at Deltares, in Delft (NL), which consists of a tank with 9.0 m of length, 5.5 m of width and 2.5 m of depth, with a multipurpose wagon on rails above it.

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.

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.