Analysis Of Combined Bearing Capacity Of Tetrapod Bucket Foundation For Offshore Wind Turbines In Sandy Soil

The development of offshore wind energy has become an important measure to realize China’s "carbon neutral" development strategy.At present,one of the key factors affecting the construction cost of offshore wind power is the selection and design of wind turbine foundation.With the trend of large-scale and deep-water offshore wind turbine construction,the tetrapod bucket foundation with advantages of both installation and bearing capacity has gradually come into people’s view.During the service process,the tetrapod bucket foundation shall bear the vertical load from the upper structure and environmental loads such as wind and waves.At the same time,when the current flows through the foundation,it will also cause local scouring effect on the soil around the foundation and reduce the bearing capacity of the foundation.Therefore,it is of great practical significance to study the bearing capacity of the tetrapod bucket foundation under the combined action of composite loads and the impact of scouring on its bearing characteristicsIn this paper,based on the finite element software ABAQUS,the tetrapod bucket foundation of offshore wind turbine in sandy soil is established,and the accuracy of the numerical model is verified through the existing model tests.Then carry out parameter analysis,considering the influence of bucket spacing,bucket depth,sand compactness and local scouring,and study the one-way and composite bearing characteristics of tetrapod bucket foundations in sand under the influence of different parameters.The main work and research results of this paper are as follows:(1)Considering the influence of parameters such as different bucket spacing,bucket depth and sand compactness,the bearing capacity and failure mechanism of tetrapod bucket suction foundation under vertical load V,horizontal load H and moment load M are studied.It is found that the vertical bearing capacity of the tetrapod bucket foundation is most significantly affected by the compactness of the sand,while the horizontal and moment bearing capacity is most significantly affected by the bucket spacing.Finally,according to the failure mechanism of the tetrapod bucket foundation in each direction obtained from the numerical calculation results,the formula of the tetrapod bucket foundation’s one-way bearing capacity considering the influence of different parameters is established,which provides a reference basis for the preliminary design of the tetrapod bucket foundation.(2)Based on the study of the one-way bearing capacity of the tetrapod bucket foundation,a numerical model of the composite bearing capacity of the tetrapod bucket foundation is established,and the V-H,V-M,H-M,V-H-M failure envelope of the tetrapod bucket foundation is calculated and drawn.According to the plotted composite bearing failure envelope,under the V-H and V-M composite loading conditions,increasing the vertical load within a certain range can improve the horizontal and moment bearing capacity of the tetrapod bucket foundation;Under the loading condition of H-M composite load,the failure envelope shows obvious asymmetric characteristics;Under the condition of V-H-M composite loading,the failure envelope is a convex surface,and increasing the vertical load can improve the H-M composite bearing capacity of the tetrapod bucket foundation.(3)A numerical model of tetrapod bucket foundation scouring in sand is established to study the influence of scouring depth on the one-way and composite bearing capacity of tetrapod bucket foundation.It is found that the existence of local scouring has little effect on the vertical bearing capacity of the tetrapod bucket foundation,but it will significantly reduce the horizontal and moment bearing capacity,and the degree of reduction will gradually increase with the increase of scouring rate.The weakening effect of scouring on the horizontal and moment bearing capacity of the tetrapod bucket foundation is also affected by the bucket spacing.In addition,the scouring action will reduce the V-H,V-M,H-M composite bearing capacity of the tetrapod bucket foundation,making the composite bearing envelope shrink inward,and the greater the scouring rate,the greater the inward shrinkage.