Study On Vertical Bearing Capacity Of Large Diameter Bucket Foundation Considering Scour Effect

The large diameter wide and shallow bucket foundation is a new form of offshore wind turbine foundation.Due to the large diameter(usually more than 30m),this new form of foundation can not only withstand the vertical load from the self-weight of the upper structure effectively,but also resist the horizontal load from wind,wave,flow and the huge moment from the bottom of the foundation.However,the surrounding soil is easily scoured away because of the large water-blocking width under the action of wave.Since bucket foundation depth is about 10 m,which can be considered shallow,it is sensitive to the soil loss caused by the scour.In this paper,considering the effect of unidirectional flow,soil on one side of the bucket foundation is scoured,and the concept of scoured ratio is introduced.The vertical ultimate bearing capacity of the bucket foundation under different scoured ratios is studied.The main contents and conclusions are as follows:(1)According to the test results of small scale models,the vertical bearing capacity-displacement curves of bucket foundation under different scoured ratios are obtained.The criteria determining the vertical ultimate bearing capacity of the bucket foundation according to the displacement are determined.Variation law of the vertical ultimate bearing capacity of the bucket foundation under different scoured ratios is revealed.The relationship between the scoured ratios and the vertical bearing capacity of bucket foundation before and after being scoured is fitted.(2)FEM is used to simulate the vertical loading process of bucket foundation under different scoured ratios in model tests.The reliability of FEM is verified.The variation law of ground failure modes when the bucket foundation is subjected to vertical load is obtained under different scoured ratios.(3)The bearing behavior of large-diameter bucket foundation under the combined horizontal load,bending moment and vertical bearing capacity is studied.V-H and V-M bearing capacity envelopes of bucket foundation under different scoured ratios are obtained by the fixed displacement ratio method and the Swipe method.The variation law of ground failure modes under the combined effects of different proportional loads is also obtained.(4)Based on the numerical simulation,the displacement field of ground is proposed to describe the one-side soil scoured condition.Asymmetric model of the critical slip surface is proposed.Through the limit equilibrium theory,a calculation method of vertical ultimate bearing capacity of bucket foundation under different scoured ratios is derived.The Terzaghi pier foundation bearing capacity formula is revised,when applied to calculate the bearing capacity of bucket foundation under soured condition.