Chapter 4: Soil–monopile interactions for offshore wind turbines

Offshore wind turbines (OWTs) are relatively new structures and are providing an increasing proportion of energy. This is due to the fact that offshore sites are characterised by stronger and more stable wind conditions than the corresponding land sites and thus have a higher capacity factor when compared with equivalent onshore turbines.

The design and construction of foundations for offshore turbines are challenging due to the harsh environmental conditions. Different types of foundations have been proposed: monopile, gravity base, jacket, suction caisson and floating anchoring systems. However, most of the offshore turbines currently in operation (UK Round 1 development) are supported on driven monopiles with diameters ranging between 3·5 and 6 m. The choice of monopiles results from their simplicity of installation and the proven success of driven piles in supporting offshore oil and gas infrastructures. The available methods for designing monopiles for OWTs (e.g. the approach suggested by DNV, 2007) are based on the methods originally developed for the offshore oil and gas industry (API, 1993). Lombardi et al. (2013) explain the obvious differences between offshore platform piles and monopiles, which are summarised below: