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With the current state of offshore wind turbine construction technology, a major marine spread is necessary for the installation of the foundation, tower, and turbine. It is advantageous for offshore installation to be integrated into a single operation. The large-scale composite bucket foundation is the basis for a one-step integrated transportation and installation technique using a specialized transport vessel. The proposed transportation and installation technique will minimize the offshore operation and maximize the proportion of work carried out onshore with consequent benefits in terms of cost, quality, and safety. The self-floating composite bucket foundation is towed into the semicircle groove of the vessel and connected to the wire ropes of a stationary crane. Then the tower and turbine are attached to the foundation at the shore and the entire unit consisting of the foundation, tower, and turbine is loaded out from the quayside, transported to the site and set down on the seabed. During transport, half of the unit's weight is taken by the hoisting system of the vessel, and the remaining half of the weight is supported by air cushions inside the composite bucket foundation. A detailed model is studied to determine the motions of the vessel with two units to confirm the viability and feasibility of such a method of integrated transportation. The draft and air cushion are two effect parameters used to determine the dynamical characteristics of the transportation structure system. The results show that a smaller draft and a greater air cushion positively contribute to a safe transportation process. The viability and feasibility of this method of integrated transportation are confirmed by determining the motions of the various elements proposed by the detailed model. V C 2013 AIP Publishing LLC. [http://dx.

Sandy ocean soil is vulnerable to liquefaction under seismic action. This paper describes the structural design of a new large-scale prestressed concrete bucket foundation (LSPCBF) for offshore wind turbines that take the seismic response of the foundation into consideration. Using an integrated finite element model of the soil, bucket foundation, and upper structure that incorporates infinite elements for the soil boundary, the dynamic responses of the upper structure, the bucket foundation, and the soil surrounding the bucket foundation to three types of seismic wave acceleration time histories were determined using time history analysis. The Shanghai artificial seismic wave was used as an example. This wave causes the most intense seismic response of the seismic waves considered, based on the anti-liquefaction shear stress approach to estimating the area of soil liquefaction. The results showed that 88% of the soil outside the bucket in the range of the bucket depth is liquefied. In contrast, only 9% of the soil inside the bucket is liquefied. As the soil depth increases, the liquefaction range decreases substantially. The simulation results show that the LSPCBF can improve the liquefaction resistance of soil inside and directly below the bucket under seismic loading. Finally, the foundation stabilities under an ultimate load before and after an earthquake were compared. The horizontal displacement of the liquefied foundation increased by 41.1% and the vertical differential settlement increased by 6.2% after the earthquake. A large plastic zone was not formed, which means that an LSPCBF subjected to seismic action is still able to support the ultimate load.

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Occurrence of liquefaction in saturated sandy deposits under structure foundation can cause a wide range of structural damages from minor settlement to general failure because of bearing capacity loss. By comparing traditional foundations for offshore wind turbines, the soil inside and underneath the composite bucket foundation is subjected to the overburden pressure from the foundation self-weight and constrained by a half-closed bucket skirt. The objective of this paper is to clarify the effects of the soil-foundation interaction on the soil liquefaction resistance around the skirt and under the foundation. The dynamic response of the composite bucket foundation during earthquake, including coupled soil mode of porous media, is calculated using the ADINA finite-element program. A typical configuration of composite bucket foundation is used for the analysis, and two earthquake waves (peak ground accelerations of 0.035 g and 0.22 g) are applied as the base acceleration. The results show that the composite bucket foundation exhibited good resistance to seismic action by improving the anti-liquefaction capacity of the soil inside and under the foundation because of the overburden pressure of the self-weight and the constraint effect of the skirt. V C 2014 AIP Publishing LLC. [http://dx.