Research On Bearing Characteristics Of Pile-bucket Composite Foundation For Offshore Wind Power Under Horizontal Loads

With the depletion of traditional energy,vigorously developing offshore wind power project has become an effective way to solve the domestic and international energy shortages.During the service period,the offshore wind turbine is affected by the horizontal load of wind and wave,which causes the basic damage and the bearing capacity to decrease.Therefore,the development of efficient and economical wind power foundation and the control of foundation Deformation become an important subject of offshore wind power research.The pile-bucket composite foundation is a new type of offshore wind power foundation.It has the characteristics of convenient construction and high bearing capacity.In order to make the foundation into engineering application,it is necessary to carry out the pile-bucket composite foundation bearing features under the horizontal static loads and dynamic loads.The main research contents are as follows:(1)Summarize the working behavior and calculation method of the pile foundation and the cylinder foundation under the horizontal load.On this basis,based on the limit ground reaction method and the bearing capacity of the PBCF,the formula of calculating the ultimate ultimate bearing capacity of the PBCF is deduced.The calculation has a high degree of credibility and safety,more in line with the actual conditions.(2)The whole finite element model of offshore wind power utilizing PBCF is established,and the top eight order frequency and Rayleigh damping coefficients are obtained.At the same time,the bearing characteristics of PBCF under horizontal static load are studied.The analysis shows that the PBCF is a soft-rigid foundation,and the dimensions of the foundation meet the requied safety frequency.The deformation of PBCF occurs around the rotation point under the horizontal static load.The deformation increases with the load increasing,and the rotation point will remain stable after moving down a certain distance.Compared with the single pile foundation with equal amount of steel,the PBCF has obvious advantage of horizontal bearing capacity and cost.(3)The finite element models of the PBCF with different load parameters,size parameters and soil parameters are established.The load characteristics of the PBCF under horizontal cyclic loading are studied by applying the sinusoidal load to simulate wind load.The results show that the number of cycles n = 10 is the cutoff point of the soil dilatation stage and the shear stage.When the number of load cycles becomes from 1 to 10,the displacement increment of the PBCF is larger,and then the increment becomes slow.After more than 1000 cycles,the displacement gradually tends to a fixed value.The horizontal displacement of the PBCF is developing violently and is no longer stable when the load exceeds a certain value.When the load frequency is at a certain value,that is,f = 0.4Hz,the lateral displacement of the foundation will be particularly violent.When the stacking load does not exceed 0.5MPa,increasing reasonably the stacking load can improve the horizontal bearing capacity.The friction angle and cohesion of the soil have little effect on the horizontal bearing capacity,and the influence of the elastic modulus and the friction coefficient on the basic horizontal bearing capacity are lager;When the pile-bucket depth ratio is no more than 10,it is an effective measure to reduce the horizontal deformation by increasing pile-bucket depth ratio reasonably.(4)The effect of seismic action on the horizontal bearing capacity of the PBCF is analyzed by applying seismic acceleration to the foundation.It is found that compared with the seismic acceleration,the horizontal displacement of the mud surface has hysteresis.The displacement of the pile top in ? site and ? site is larger,and the calculation of the seismic action by the Taft wave will make the result safer.