Study On Deflection-based Bearing Capacity Of Suction Caisson Foundations Of Offshore Wind Turbines

As one of the most important and technology-matured renewable energy, wind energy is a significant direction of global energy development strategy. China has abundant offshore wind energy resources, which is of great significance to the vigorous development of offshore wind power. The foundation works as the ultimate undertaker of the upper load, therefore the design of the foundation has a critical influence on the whole wind turbine design. Suction caisson foundation has shown its considerable prospects in engineering applications because of its low costs and convenient construction. Aiming at more and more offshore wind turbines constructed in silty or sandy seabed in China, a program of large-scale1g model tests were carried out in silt to obtain the deformation and mechanical characteristics of suction caisson foundation. Strictly control to rotation angle must be considered when the wind turbine foundation is in normal operation. A bearing capacity analysis approach based on deformation is proposed.A series of model tests at1g on suction caissons with different dimensional sizes subjected to overturning loading were carried out in sandy silt to investigate its deformation mechanism and bearing capacity characteristics. The test results reveal the effects of the diameter, aspect ratio, and loading eccentricity on normalized moment capacity of caissons, as well as different rotation center positions of caisson foundation. A new calculation approach of deflection-based bearing capacity was proposed based on the mechanisms of deflection and soil-structure interaction of the caisson and determination of the computation parameters were discussed. The present analytical approach can predict the moment-rotation curves of the model tests in silt and the field test in sand in a good manner. This deflection-based approach makes it possible to calculate bearing capacity at any allowable angular rotation. Further studies show that the soil pressures and the friction on the outer skirt at passive zone contribute most to the moment capacity of the caisson, and concretely the aspect ratio and constant of horizontal subgrade reaction have the greatest influence on the moment capacity.As for multi-caisson foundation, the role of pulling caisson in resistance to wave loading was mainly considered. Series of model tests on suction caissons with different sizes subjected to pulling loading were conducted to investigate the influence of different loading rates on pulling capacity and the effects of suction and the response of the soil to caisson’s pulling out, based on which, horizontal static and cyclic loading model tests on multi-caisson were also carried out, using the three-degree-of-freedom force sensor to obtain the real force condition of each caisson. Through the tests the analysis approach of ultimate overturning capacity of multi-caisson foundation was discussed, meanwhile the accumulated deformation of multi-caisson under different loading levels and the force development of each caisson were also investigated.