Interactions in offshore foundation design

Abstract

This paper presents some examples of design problems for offshore foundations, drawn from the jack-up industry and the wind turbine industry. The examples are chosen to illustrate some general points about foundation design, geotechnical engineering and its interaction with other disciplines. The first example is drawn from the assessment of the safety of installation of jack-up units (large mobile offshore drilling rigs). It illustrates how more rational approaches can be achieved through a deeper use of probabilistic methods in both the prediction of performance and the assessment of field observations. The second example also comes from jack-up practice, but has wider application too: it addresses the classical problem of the performance of foundations under combined loading, and how this can be understood in a simple theoretical and practical framework based on plasticity theory. The final example comes from the renewables sector, where the rapidly expanding offshore wind industry poses new foundation challenges for geotechnical engineers. Practical and economic foundation solutions are required if the UK is to meet its ambitious plans to exploit larger turbines in deeper waters. Both conventional (monopile) and novel solutions (suction caissons, screw piles) to the foundation problem are discussed. The paper also demonstrates how interactions with other disciplines can enrich geotechnical engineering, illustrated by specific practical examples from the Author's experience.

A finite element approach for determining the full load–displacement relationship of axially loaded shallow screw anchors, incorporating installation effects

“…Screw anchors or piles are a founda on technology that may provide significant upli capacity for offshore applica ons (Byrne and Houlsby 2015;Houlsby 2016) while avoiding pile driving nuisance for marine inhabitants (Bailey et al 2010). Screw anchors consist of one or more steel helices (150-400mm diameter), a ached to a core of smaller diameter and are used onshore to anchor rela vely light structures (Perko 2009).…”

Input of fully 3D FE soil-structure modelling to the operational analysis of jack-up structures

“…A typical issue in this context is the evaluation of the moment-rotation response at each spudcan, commonly referred to as spudcan fixity. To perform sound structural analyses, engineers must decide whether leg-seabed connections can be treated as pinned, fixed or deformable rotational constraints (Houlsby, 2016). The last, most realistic case is in fact quite hard to handle, as the overall spudcan-soil stiffness evolves during operations depending on multiple factors (e.g.…”

“…At the highest levelthe so-called Displacement Check -the ISO standard requires finite element (FE) jack-up analyses including soil non-linearities and large deformation effects, so as to capture the consequences of foundation displacements through integrated soil-structure simulations (Wong et al, 2012;Purwana et al, 2012). As noted by Houlsby (2016), "the important interaction at this stage is with structural engineers, who need to be able to analyse the forces in the structure, and for rather flexible structures such as jack-up units the structural forces depend critically on the foundation response". This work highlights the relevance of integrated 3D FE soil-foundation-structure modelling for the ISO Displacement Check (Level 3), with focus on the continuum simulation of non-linear soil-spudcan interaction.…”

3-Dimensional numerical study of wave-induced seabed response around three different types of wind turbine pile foundations

“…In the past two decades, there has been intensive development of offshore engineering around the globe in search of alternative power source, most especially offshore wind turbines [3,4]. However, the immense marine constructions have attracted interest from coastal engineers, geotechnical experts, and scientific researchers in the discipline of offshore engineering to examine the WSSI phenomenon.…”