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www.sea-technology.com September 2014 / st 39 A lthough comprising less than one percent of the initial outlay of an offshore wind farm, foundation grout- ing is crucial for the structural integrity of the turbines and therefore their lon- gevity and future capacity to generate power. With the U.K. committed to ob- taining 15 percent of its energy require- ments from renewable sources by 2020, cost reduction in all areas of wind farm development is essential, and founda- tion grouting is no exception to this. In- dustrialization is key in offshore wind. Projects and techniques must be com- mercially viable on a large scale. In oil and gas projects, it is com- mon to install single or small groups of jacket structures; therefore, while many techniques have been transferred to off- shore wind, adaptations have had to be made to ensure scalability. At Gwynt y Môr offshore wind farm, 13 miles off the coast of North Wales, FoundOcean (Marlow, England) grouted 160 mono- pile foundations, demonstrating the large scale of projects in offshore wind. The second largest wind farm in the U.K., Gwynt y Môr is capable of gener- ating enough power to meet the needs of 400,000 homes. Foundation Design Grouting the foundations of an offshore wind farm in- volves securing the turbine to the supporting foundation structure, and/or the foundation structure to the seabed, of- ten via a grouted connection. There are a number of foundation types currently used in offshore wind farm construction. The majority of the world's offshore wind farms use monopile foundations, the most cost-effective option for turbines of up to 5 megawatts, and in water depths of up to 25 meters. Monopiles consist of a Building Firm Foundations For Offshore Wind The Importance of Foundation Grouting for Long-Lasting Turbines By Jim Bell A monopile transition piece at Gwynt y Môr. 4.5-to-9-meter diameter, hollow steel pile driven into the seabed. A transi- tion piece is then placed over the steel pile, providing the leveling mechanism for the turbine tower. Grout is pumped into the annulus between the monopile and transition piece. As turbines exceed 5 megawatts and wind farms move further offshore into deeper water, jacket foundations are increasingly being exploited. The jacket structure, similar to those used in oil and gas projects, lends itself well to adaptation for use in offshore wind. The designs have been modifed, hav- ing longer piles driven deeper into the subsoil, to provide more stability due to the height of the turbine blades. The annuli between the piles and the jacket legs are grouted. The Energy Park Fife Samsung 7-megawatt turbine is an example of a FoundOcean-grouted jacket structure housing a large turbine. In fact, at the time of installation, the turbine was the world's largest; each blade measures more than 80 meters, longer than the wingspan of an Airbus A380. It took 909 tonnes of ultrahigh-strength ce- ment to complete the foundation grouting of the 500-tonne, four-legged steel jacket. The piles were inserted into pre- drilled rock sockets and then grouted to secure the connec- tion. The annuli between the jacket legs and the piles were also grouted. Other foundation types include adaptations of monopile- type structures, including tripods with three piled connec- tions close to the seabed, or tripiles with three piles con- nected above the water via a grouted transition piece. Both provide a larger footprint than a typical monopile founda- tion, making them more suitable for softer seabeds or deep- er water.