Abstract
Monopiles, due to their simplicity in shape and easy fabrication, are a preferred option for supporting offshore wind turbines. As the turbines are getting larger (i.e., 12–15MW), the monopiles required to support them are also getting heavier, larger, and longer. The chapter aims to investigate the effects of adding a plate/collar to a monopile at the mudline level. The new foundation (monopile + plate) can be termed a hybrid foundation as this is a combination of shallow and deep foundations. As codes of practice to design such systems are unavailable, a numerical model is developed to analyze such hybrid systems to obtain the design parameters. The developed numerical model is validated using data from centrifuge-based scaled model tests. The validated model is used to carry out sensitivity analysis of different plate diameters and pile lengths. The study showed that using the hybrid foundation reduces the embedded length of the monopile. Furthermore, adding a plate enhances the stiffness and ultimate load-carrying capacity of the foundation. It is envisaged that adding a plate can also retrofit existing distressed monopiles and repower and life extension of existing wind farms.