Research Of A New Type Of Foundation For Offshore Wind Turbines With The Combining Of Monoplie Foundation And Bucket Foundation

Pile-bucket foundation is a new type of foundation for offshore wind turbines,which is a combination of both monopile foundation and bucket foundation.Compared to the monopile foundation, pile-bucket foundation changes the mode ofbearing and deformation and reduces the amount of steel by reducing the length andthickness of the pile. The positioning of pile can be guaranteed by the bucketfoundation. Compared to the monopile foundation, pile-bucket foundation can beargreater loads and be applied to the high-power wind turbines when they are under thesame weight. Based on the existing bearing and deformation theory of pile foundationand bucket foundation, two kinds of the ultimate vertical failure mode and one kind ofthe ultimate horizontal failure mode were established. The formula for vertical andhorizontal bearing capacity of pile-bucket foundation in the sand foundation and clayfoundation were also established. So, the impact of different parameters on theperformance of vertical and horizontal bearing capacity can be analyzed. It has beenfound that the vertical bearing capacity increases with the increasing of the bulkdensity of soil, the shear strength of soil, the depth of pile, the diameter of pile, thediameter of bucket and the depth of bucket. The horizontal bearing capacity increaseswith the increasing of the shear strength of soil, the depth of pile, the diameter of pileand the diameter of bucket. In this paper, the general-purpose finite element analysispackage ABAQUS was used to conduct three-dimensional numerical analyses. Basedon the force and displacement control process, the influencing factors for bearingcapacity behavior of the pile-bucket foundation were analyzed and compared. Theresults show that the impact factors of bearing capacity and deformation of the FEresults agree well with the theoretical analysis results. To meet the requirements ofeconomy, the depth of the pile can be equal to4-6times of the diameter of pile, andthe thickness of the pile can be equal to1/100of that. Also, the diameter of the bucketcan be equal to2-4times of the diameter of pile, and the depth of the bucket can beequal to one or half of that. Based on the loads and geological conditions of actualproject, the monopile foundation and pile-bucket foundation for3MW offshore windturbines were designed. Compared to that of monopile foundation, the levelness anddisplacement of pile-bucket foundation is low and the bearing performance is good when they are under the same weight. The pile-bucket foundation will be destroyedby rotating around a point under the ultimate loads, from which some suggestions aregiven for engineering practice.