Research On Bucket Foundation And Subsoil Interaction Subject To Static And Dynamic Loadings On Offshore Wind Farm

The offshore wind turbine foundation always undertakes the multi-dimensional loadings with large overturning moment.For this reason,the shallow bucket foundation with the advantages of superior anti-overturning bearing capacity and low cost of construction and transportation is gradually used in the construction of offshore wind turbine.Due to the large diameter and small ratio of height to diameter,the shallow bucket foundation has obvious differences with the typical suction anchor.Under the condition of multi-dimensional loadings,the bucket lid of shallow bucket foundation undertakes a part of soil resistance.The complex interaction between the shallow bucket foundation and soil is the key to estimate the bearing capacity of shallow bucket foundation.This paper presents a series of small-scale model tests,centrifuge static tests and centrifuge dynamic tests.With the combination of tests results and the numerical simulation results,the paper reveals the regularity of incomplete cooperation between the bucket and soil under the overturning moment.The calculation method of antioverturning bearing capacity of the shallow bucket foundation is derived.The modified calculation method considering soil strength reduction and the beneficial effect of foundation weight under the cyclic lateral loading and seismic loading has also been obtained.The specific research contents are as follows:(1)The separation between bucket and subsoil is revealed based on the large scale model tests.The tests phenomenon shows the bucket-soil incomplete cooperation with the condition of overturning loading.The concept of bucket-soil cooperative degree is defined based on the phenomenon of bucket-soil incomplete cooperation in large-scale model tests.The influences of the parameters including loading condition,dimension of bucket foundation,bucket compartment form,height and thickness of bulkheads and bucket-soil relative stiffness on bucket-soil cooperative degree are analyzed by numerical simulation method.The beneficial effect of bucket-soil cooperation on the bearing capacity of bucket foundation is presented.(2)The influence of incomplete cooperation between the bucket and soil is analyzed.The failure envelopes method is used to compare the multi-dimensional bearing capacity between the shallow bucket foundation and the solid foundation.The difference reveals that the bucket-soil incomplete cooperation caused by the overturning moment decreases the multi-dimensional bearing capacity of the shallow bucket.(3)The overturning failure mode considering the bucket-soil incomplete cooperation is proposed based on the results of numerical simulation and centrifuge tests.Then the limit equilibrium calculation method is proposed to calculate the antioverturning bearing capacity of the shallow bucket.(4)The mechanism of the influence of cyclic loading on deceasing the antioverturning bearing capacity is revealed.The quantitative relation between cyclic loading amplitudes and reduction of anti-overturning bearing capacity is conducted.Based on the pore water pressure accumulation of soil inner the bucket,the pseudo static calculation method of anti-overturning bearing capacity is proposed with the consideration of long-term cyclic loadings.(5)The seismic responses of the shallow bucket and the soil are studied.The regularities of lateral acceleration,pore water pressure and the lateral strain are obtained through a series of centrifuge seismic tests.The influence of the shallow bucket on decreasing the pore water pressure accumulation of the soil influenced by the selfweight of bucket is revealed.The tests results show that compared with the accumulation of uninfluenced area,the minimum reduction degree of accumulation of pore water pressure is 20%.