The Research Of Structural Optimization And Bearing Capacity Characteristics Of Composite Pile Foundation For Offshore Wind Power

Presently, pile foundation is widely applied as a form of foundation for offshorewind turbines. And wind turbine foundation subjected to loads in the marineenvironment will be larger with the increase of the installed capacity of offshore windturbines. In order to effectively control the horizontal displacement of pile foundation,the method of enlarging the pile diameter or increasing the depth of the buried pilewill be taken in general. However, this method not only increases the steel tonnage ofthe pile, but also proposes a higher piling construction requirement, which leads to anelevated cost of the pile foundation, an increase in construction difficulty, as well as agrowth in the construction cycle. Against this background, the proposing of compositepile foundation gives a good solution to these problems, and effectively reduces thecost of wind power development using pile foundation, which makes significanteconomic benefits.Composite pile foundation is a new form of offshore wind power foundation,which is composed of pile foundation and the cylindrical foundation mounted on theperiphery of the pile body, whose unique form of structure makes the foundation havea good level of bearing performance. In this paper, composite pile foundation is takenas the research object, and the study is mainly about shape optimization of compositepile foundation and bearing characteristic of the foundation under lateral loads.Specific details go as follows:(1) The structure form and construction process of composite pile foundationare described, as well as the great advantages in bearing performance of compositepile foundation under lateral loads. Composite pile foundation is suitable forhigh-power offshore wind power generators, which is well suited to the developmenttrend of offshore wind power.(2)According to Winkler assumption, for composite pile foundation underhorizontal loads, distributed forms of soil resistance on the side of the foundation, aswell as resistance of the pile body and the soil at the bottom of the barrel side aregiven. Based on the elastic subgrade reaction method in theoretical deformation offoundation, the formula of bearing capacity for composite pile foundation underhorizontal loads is derived.(3)Using three-dimensional finite element analysis method, the impact of burieddepth, pile diameter, cylinder diameter and height dimensions of the cylinder wall for a single pile in composite pile foundation on horizontal bearing characteristic of thefoundation is systematically studied, and the impact of the set of the ribs, thickness ofthe transition section, as well as cylinder cover heap on horizontal bearing capacityand structure stress distribution of the foundation.(4)Taking the satisfaction of bearing capacity design requirements for compositepile foundation as the constraints, and the minimum amount of steel as the objectivefunction, the size of composite pile is optimized in certainty based on SQPoptimization theory. The bearing capacity and strength are also checked for theresulting foundation using finite element software, to get the optimal design size ofcomposite pile foundation finally.(5)According to the resulting optimizing size of the model, finite element modelis established and analyzed, and the ultimate horizontal bearing characteristic ofcomposite pile foundation is studied systematically. The distribution form of earthpressure along pile of composite pile foundation under lateral loads is analyzed, aswell as the failure mode of composite pile foundation under ultimate lateral loads.