| The bucket foundation,as a new type of deep-water foundation structure,has been gradually developed and applied in offshore engineering field,which makes up for the shortcomings of single pile foundation and gravity foundation.In offshore wind turbine projects,due to the complicated hydrologic and climatic conditions,soil conditions and load conditions,the traditional foundation design scheme only depends on the designer’s experience may not achieve the reasonable allocation of resources,a lot of work needs to be done to study the suction foundation.At present,the research of bucket foundation mainly focus on the analysis of the mechanical properties of single type,but the research on the mechanical properties and failure mechanism of multi-bucket foundation in sand foundation is not enough.In view of the above background,this thesis analyzes the failure mode and bearing characteristics of tripod-bucket foundation under horizontal and bending moment loads by means of small scale model test,and verifies and expands the test results by PLAXIS finite element method.Finally,the size of the tripod-bucket foundation is optimized by mathematical method,which provides the optimal design scheme for an actual project.The main work of this thesis includes the following contents:The bearing capacity and failure mode of tripod-bucket foundation under horizontal and bending moment load are studied by means of PLAXIS and model test.It is found that the ultimate bearing capacity of tripod-bucket foundation in sand can be determined by the characteristic points in the load-displacement curve.Under the same horizontal and bending moment load conditions,with the decrease of the ratio of length to diameter,the horizontal displacement of the tripod-bucket foundation is smaller.The failure mode of foundation under horizontal and bending moment shows that in the early stage of loading,the main movement trend of foundation is rotation and translation.At the failure stage,the whole foundation is overturned.When the tripod-bucket foundation trends to rotate,the rotation center of the whole structure is located near the axis of the compression tube,and moves down with the decrease of the length to diameter ratio.According to the bearing capacity characteristics of tripod-bucket foundation under combined loading mode,the failure envelope in the M-H stress space is searched by using the fixed load ratio method with the finite element PLAXIS.This thesis discusses the theoretical calculation method of horizontal and bending moment bearing capacity of tripod-bucket foundation,and proposed the efficiency coefficient of bearing capacity and the correction coefficient for bearing capacity calculation s on the basis of the existing theory.Through numerical simulation and model test,the bearing characteristics of tripod-bucket foundation under different bearing capacity factors are systematically discussed.The influence of the change of the ratio of length to diameter on the horizontal bearing capacity of the tripod-bucket foundation under the same caissons’ weight is studied.According to the different action directions of horizontal and bending moment load,the most favorable and unfavorable directions of horizontal loads on the tripod-bucket foundation are determined.The influences of different bucket spacing on the bearing capacity of tripod-bucket foundation under the same size and load direction are discussed,and the concept of bearing capacity growth efficiency coefficient to determine the optimal spacing between buckets are introduced.Based on the research conclusion of the bearing capacity characteristics of the tripod-bucket foundation,the mathematical optimization model is established,and a practical project of offshore wind turbine is redesigned for size optimization.The stability of the optimized structure is verified by the finite element method.The results show that the optimization scheme results in a greatly saving of materials and so cost. |
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