2307
Modelling of monopile-footing foundation system for offshore structures
in cohesionless soils
Modélisation d’un système de fondation superficielle isolé pour sur les structures maritimes dans
les sols pulvérulents
Arshi H.S., Stone K.J.L.
University of Brighton, UK
Vaziri M.
Ramboll UK Limited, UK
Newson T.A., El-Marassi M.
University of Western Ontario, Canada
Taylor R.N., Goodey R.J.
City University London, UK
ABSTRACT: While monopiles have proven to be an economically sound foundation solution for wind turbines, especially in
relatively shallow water, their installation in deeper water and in hard ground may require a more complex foundation design in order
to satisfy the loading conditions. One approach is that foundation systems are developed which combine several foundation elements
to create a ‘hybrid’ system. In this way it is possible to develop a foundation system which is more efficient for the combination of
vertical and lateral loads associated with wind turbines while maintaining the efficiency and simplicity of the design. Previous studies
have reported the results of single gravity tests of the hybrid system where the benefits of adding the footing to the pile are illustrated.
This paper presents experimental results on the performance of skirted and unskirted monopile-footings. A simplified design approach
based on conventional lateral pile analysis is presented.
RÉSUMÉ : Alors que les fondations de type monopile se sont révélées être une solution économiquement viable pour les fondations
d’éoliennes, en particulier dans les eaux relativement peu profondes, leur installation dans des eaux plus profondes et dans un sol dur
peut exiger une conception plus complexe afin de satisfaire les conditions de chargement. Une approche possible est que les systèmes
de fondations développés combinent plusieurs éléments de fondation pour créer un système hybride. De cette manière, il est possible
de développer un système de fondation plus efficace vis à vis des charges verticales et latérales associées aux éoliennes, tout en
maintenant une conception efficace et simple. Des études antérieures sous gravité simple ont montré l’efficacité d’un système hybride
en combinant une semelle et un pieu . Cet article présente des résultats expérimentaux sur la performance de systèmes avec et sans
pieu pour des semelles. Une approche de conception simplifiée basée sur l'analyse classique d’un pieu sous charge latérale est
présentée.
KEYWORDS: Hybrid monopile footing, offshore piles, laterally loaded piles, wind turbine foundations
1 INTRODUCTION
Due to the needs of on-going developments in the oil and
energy sector, the design of offshore foundations is constantly
evolving. In the hydrocarbon extraction sector, exploration and
development is moving in to ever deeper water resulting in ever
more challenging geotechnical conditions. Similarly the
expansion of the offshore wind sector involves the development
of deepwater sites, together with requirements for heavier high
capacity turbines. Conventional offshore foundations are not
always economical or practical for this new generation of
turbines, and there remains a requirement to develop foundation
solutions which can better satisfy future developments in the
offshore wind sector.
The foundations of a typical offshore wind turbine are
subjected to combined loading conditions consisting of the self-
weight of the structure (V), relatively high horizontal loads (H)
and large bending moments (M). The preferred foundation
system to date has been the monopile, which has the advantage
that it can be employed in a variety of different soil conditions.
However, a disadvantage in the use of monopiles in deep water
sites is that the system can be overly compliant. For sites with
intermediate water depths, it may be possible to stiffen the
lateral response of the monopile at the mudline.
Figure 1. Schematic illustration of the prototype hybrid system.
One such approach to increase the lateral resistance of a
monopile is the ‘hybrid’ monopile-footing system. As
schematically represented in Figure 1, this foundation system
