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Suction bucket installation in pure clay or pure sand is well established. However, in layered soils, particularly in sand over clay soils, the soil plug uplift is considered a major installation risk and feasibility of installation is often questioned. In this paper, the experience from installation of two suction bucket jackets at two offshore wind farms in layered soils is reported. The installation at both sites was successful and no excess plug uplift was observed. The transfer of suction to the clay-sand interface is believed to have contributed to the success of the installations. The two cases presented in this paper provides confidence in suction bucket foundation installation in similar soil conditions. [ABSTRACT FROM AUTHOR]

Abstract Large diameter steel pipe pile foundations, typically known as monopiles, are the predominant foundation solution for offshore wind turbines. This paper deals with soil reaction curves for monopile analysis under lateral loading in clay. Developed from extensive parametric finite element analyses, models are proposed that allow for construction of site-specific soil reaction curves based on the stress-strain responses measured in laboratory tests. Assisted by failure mechanisms revealed by finite element analyses, a conceptual framework is proposed to analyse the monopile response under lateral loading using the beam-column approach. The conceptual framework makes use of the p-y model for wedge failure developed in this study along the monopile above the rotation point, existing p-y model for the flow-around failure suggested in the literature below the rotation point and base shear s-u model developed in this study at the pile tip. Validation exercises against finite element simulations and field pile testing results demonstrate excellent capability of the framework to predict monopile responses. The soil reaction models proposed in this paper provide practising engineers with a simple yet powerful approach to use site-specific soil reaction curves in monopile design based on element soil behaviour measured in laboratory, without the need for advanced numerical analyses. Highlights • Soil reaction models that use stress-strain responses measured in laboratory tests as input. • Site-specific soil reaction curves can therefore be used in design, without the need for advanced site specific finite element analysis. • A conceptual framework for monopile analysis using a conventional beam-column approach. [ABSTRACT FROM AUTHOR]

The fatigue assessment of a well conductor is a critical design task during offshore exploration and development of hydrocarbons. In recent years, major progress has been made towards the modelling of soil-conductor interaction. Upgraded soil-conductor interaction springs (i.e., p-y curves) and damping models are developed and are gaining acceptance by the industry. However, there is a general lack of simplified procedures to incorporate the soil damping into the time-domain structural analysis of a wellhead system. Thus, the motivation of this paper is to close this gap by proposing a simplified procedure for incorporating the soil damping in the well conductor time domain analysis. The procedure is generic and allows for convenient adoption of alterative p-y spring and damping models. Design charts for equivalent soil system damping ratio versus the lateral deflection of the conductor are developed through parametric analyses based on representative wellhead configurations with typical soil strength profiles in the Gulf of Mexico to facilitate practical design. • A simplified procedure for incorporating the soil damping in time domain analysis of well conductors. • Design charts are developed for representative wellhead configurations and soil strength profiles in the Gulf of Mexico. [ABSTRACT FROM AUTHOR]

Large-diameter monopiles are the predominant foundation solution for supporting offshore wind turbines. They are conventionally designed using soil reaction curves developed for long slender piles used for supporting offshore oil and gas platforms (e.g., the API p-y model). However, due to the difference in the length/diameter ratio and the resulting soil mechanisms, the use of p-y curves alone can lead to significant under-prediction of the lateral stiffness and capacity of monopiles. To overcome the shortcoming, the authors have previously proposed a conceptual two-spring framework, i.e., the so-called ' p-y + M R - θ R ' model, to capture the monopile response in soft clay under lateral loading. The framework uses distributed p-y springs to consider the lateral soil resistance along the pile above the rotation point (RP) and a single moment-rotation (M R - θ R) spring attached at the RP to capture the entire soil resistance below the RP, i.e., the distributed resistance along the pile, base shear and base moment at the pile tip. The proposed p-y and M R - θ R springs were curve-fitted to the results of 3D numerical analyses. However, as the stress-strain response and the shear strength profile inevitably influence the p-y and M R - θ R springs, the applicability of the empirical formulations to soil conditions other than those examined is uncertain. This study proposes an enhancement to the ' p-y + M R - θ R ' framework, in which the p-y and M R - θ R springs are not tied to a specific soil and strength profile but fundamentally linked to the properties that can be measured directly in the site investigation and laboratory. This extension is achieved through analytical analyses and an extensive parametric numerical study. The predictive capabilities of the model are demonstrated by back-analyses of finite element analyses and centrifuge model tests. The proposed model provides practising engineers with a simple yet powerful approach to use site-specific soil reaction curves in the design of monopiles embedded in soft clay. • A two-spring framework for monopile analysis in soft clays. • Soil resistance below the rotation point is lumped into a single moment-rotation spring. • Both p-y and M R - θ R springs are fundamentally linked to soil stress-strain response. • Validation against 3D finite element analyses and centrifuge model tests. • Model demonstrates a clear improvement over the current design method. [ABSTRACT FROM AUTHOR]

The offshore wind farm industry in China has been growing exponentially in recent years, and suction bucket foundations are increasingly applied as an effective solution. This paper presents a comprehensive site investigation and outlines the key soil parameters for offshore suction bucket foundation design, by taking the Houhu wind farm in southern China as an example. The in-situ cone penetrometer (CPTU) tests and sampling borehole were carried out to investigate the geotechnical features of soils. The soil conditions are characterized by multilayers and complicated sediment components. The classification and mechanical properties, such as stress history, static and cyclic shear strengths, and shear modulus of soils were obtained and compared by CPTU interpretation and advanced laboratory tests. Then the probable foundation optimization design solution from the perspective of soil parameters in the light of set up effect and cyclic behavior was discussed and highlighted. Based on the experience of this project and other projects in offshore China, some common challenges were summarized and the relative recommendations were proposed finally. The main objective of this study is to provide more reliable guidance of geotechnical investigation for the rapid development of wind farms in offshore China. • A comprehensive site investigation was carried out for the offshore suction bucket foundation design in southern China. • The classification and mechanical properties of soils were obtained and compared by CPTU interpretation and advanced laboratory tests. • The probable foundation optimization design solution was discussed and highlighted. [ABSTRACT FROM AUTHOR]