Analysis Of Horizontal Bearing Characteristics Of Pile-Bucket Hybrid Foundation For Offshore Wind Turbine

With the development of global industrialization,energy shortages and environmental pollution are emerging to various degrees around the world.and the development of renewable and clean energy has become one of the most significant measures to solve energy and environmental problems.Among them,the construction of offshore wind farms can effectively use the offshore wind energy,which accounts for 70% of our total reserves.In order to cope with the trend towards deeper and larger offshore wind farms,it is particularly important to develop efficient offshore wind foundations with good load-bearing capacity.In this paper,the horizontal bearing characteristics and deformation characteristics of pile and barrel composite foundation are studied by physical model test and numerical simulation analysis,the main work and results are as follows:(1)Physical model testOne-way static load test: the increase in the bucket diameter or height of the pile-bucket hybrid foundation significantly improves the initial stiffness of the foundation and effectively increases the bearing capacity of the foundation.Displacement-controlled cyclic loading test: the foundation under the action of displacement-controlled cycle appears sandy soil cyclic dense effect and subsidence pit effect,and the two constantly play in the loading process.The pile-bucket hybrid foundation combines the bearing capacity advantages of pile foundation and bucket structure to improve the foundation resistance to deformation and effectively control the foundation deformation.Force-controlled cyclic loading tests: The incorporation of the bucket structure improves the foundation’s ability to resist deformation.Different cyclic amplitude loading sequences have a significant influence on the deformation characteristics of pile-bucket hybrid foundation.While keeping the total load constant,the foundation deformation is small when the cyclic load in the earlier stage is less than the cyclic load in the later stage.When the cyclic load on the foundation changes in magnitude,the average cumulative displacement decreases compared to the previous period due to dense cyclic loading in the positive direction.(2)Numerical simulationThe damage mode of pile-bucket hybrid foundation is rotational damage,the load level increases,the foundation bucket diameter or bucket height increases,will cause the foundation rotation centre to move towards the horizontal load direction.Increasing the bucket height or diameter of the pile-bucket hybrid foundation can effectively resist the foundation deformation and improve the foundation bearing capacity,but when the bucket height exceeds a certain limit(1.5d),its ability to improve is weakened.When the bucket diameter increases the ultimate bearing capacity of the foundation grows more slowly in loose sand foundation than in medium dense sand and dense sand foundation.The incorporation of the barrel structure in loose sand foundations has the most significant effect on the improvement of the monopile foundation bearing capacity.Comparison of the improvement ratio between the numerical simulations and the physical model tests shows that the data fits well and the validation error is less than 20%.The horizontal load of pile-bucket hybrid foundation decreases with the increase of loading height.In a pile-bucket hybrid foundation,the bucket is mainly subjected to horizontal loads and the pile is mainly subjected to moment loads.In dense sandy soils,pile-bucket hybrid foundation is more conducive to the overturning resistance of bucket structures.Compared to monopile foundations,pile-bucket hybrid foundation exhibit superior load bearing characteristics during normal use,providing a more reliable foundation for the normal operation of the wind turbine.The load capacity can be increased by 10% to 150% for different bucket sizes.The vertical load has little effect on the horizontal bearing characteristics of pile-bucket hybrid foundation.By dimensionless normalization of the numerical simulation results,the fitted equations for the horizontal ultimate bearing capacity of the pile-bucket hybrid foundation under different foundation conditions and the ultimate bearing capacity equations under different eccentric distances are given.