Geotechnisches Site Specific Assessment für Jack-Up-Schiffe von Offshore-Windparks

Geotechnical Site Specific Assessment for offshore-wind jack-up vessels.

Jack-up vessels are widely used for installation of foundations and turbines during the construction of offshore-windfarms. Equipped with moveable legs, these vessels are able to elevate their hull out of the water and provide a stable work platform. At the same time the leg-soil-interaction increases the complexity of the operation which is reflected in the requirement to perform site specific assessments at any jacking location. Subsequent to the description of the phases of a typical jacking operation the article outlines the main components of the geotechnical part of a site specific assessment. The governing load cases are introduced and an overview of the required soil investigations is given. In the following the focus is set on the determination of the bearing capacity and the derivation of related leg penetrations for the jack-up vessel. Phenomena like the "punch-through" and their effect on the process are explained. For a typical North Sea windfarm with non-cohesive soils the accuracy of the leg prediction is shown by comparison to measured data and the major influencing parameters are discussed. Finally, a CPT-based correction method for the capacity of the upper soil layers is introduced.