Large-Scale Model Test Study On Suction Caisson Foundations For Offshore Wind Turbines

Wind energy is the most rapidly developing and prospective regenerated Energy. For the development of offshore wind energy, a novel shallow foundation type is used in place of piles, which can be described as upturned buckets and is usually called suction caisson foundations. In this thesis, some key problems in the application of suction caisson foundations were discussed, including the suction installation, pullout behavior, soil-structure interactions and cyclic loading effects.A programme of large-scale model tests on suction installation and loading of caisson foundations in saturated silt were carried out in a large soil tank at Zhejiang University. Test results during suction installation showed that the influences of seepage on penetration resistance are very limited in silt. The deformation mechanism and soil-structure interaction of a caisson subjected to overturning loads were investigated. Based on the assumption of a common position of the instantaneous rotation center and dominating resistance forces on the caisson, an analytical expression for the ultimate moment capacity was presented. Pullout test results with different loading rates indicated that loading rates have little effects on the performance caisson foundations. Ultimate pullout capacities of the caisson in silt for different loading conditions were presented then. Behaviors of suction installation and overturning loading of multi-caisson foundations were also studied by experimental work. It was found that the ultimate overturning capacity of multi-caisson foundation during a storm would be largely improved if pullout capacity of the upwind caissons can be taken into consideration. An approach to predict the elastic deformation of the multi-caisson foundations was proposed based on stiffness matrix for mono caisson foundations and the results showed that it can give fairly reliable results in the initial phase of loading.