Installation of Monopiles for Offshore Wind Turbines—By Using End-Caps and a Subsea Holding Structure

Monopiles are commonly used as foundations for offshore wind turbines at sites with shallow to intermediate water depths (say, up to 40m water depth). The installation of a monopiles is normally carried out by using a bottom supported platform (e.g., a jack-up vessel) which holds the pile at the correct location vertically while driving it into the seabed. In this paper, a methodology for installing a monopile is described which can be applied either by a bottom supported platform or by a floating vessel. The basic philosophy behind this methodology is to support the monopile initially by buoyancy and then by a subsea holding structure. Thus the requirement for a large crane working offshore is eliminated and the marine operation is no longer dependent on the motions of the supporting vessel. Brief geotechnical calculations are presented to support the feasibility of this methodology. Some of the possible design challenges of the installation aids are listed in the conclusion.