Research On Bearing Capacity Of Wide-shallow Bucket Foundation For Offshore Wind Turbine Under Multi-dimensional Loading In Clay

Offshore wind power is one of the most important energy sources of China developed in recent years.As a new type of the offshore wind power foundation,the large diameter,wide and shallow bucket foundation has a good ability to withstand the overturning moment,therefore it is suitable for the soil with many soft clays in Chinese offshore.And this type of foundation has the characteristic of shore prefabrication,foundation-tube-fan integrated floating transportation and installation resulting in a good benefit of economy.To better realize the bearing characteristic of the wide and shallow bucket foundations,this paper systematically studies the uniaxial and combined ultimate bearing capacities of the offshore wind foundation by means of numerical analysis,laboratory model test,centrifuge test and upper bound solution limit analysis according to the multi-dimensional loading characteristics of offshore wind foundations.The main research contents and specific results are as follows:(1)Numerical analysis was used to study the uniaxial ultimate bearing characteristics of the bucket foundation,and the vertical,anti-slip,horizontal and antiovertuning ultimate bearing capacities and corresponding failure mechanisms were obtained.The numerical results were verified by using laboratory model tests and centrifuge tests.(2)The corresponding upper bound solution limit analysis for uniaxial ultimate bearing capacity was established combined with the virtual work equation and the internal energy loss rate function,the velocity field and the failure mechanisms of the bucket foundations.The upper bound solutions for the vertical,anti-sliding,horizontal and anti-overturning ultimate bearing capacities of the bucket foundations were programmed using Matlab mathematical software.The influence of the bucket-soil contact behaviour on the uniaxial ultimate bearing capacity of barrel-type foundations were discussed in the upper limit solution of the ultimate analysis.The upper bound solutions for the vertical and anti-sliding bearing capacity considering the interaction of the side wall-soil.And the upper limit solutions for the anti-sliding bearing capacitis that take into account the disengagement phenomenon between the back wall and the soil is studied based on the test results.(3)Numerical methods are used to analyse the position of the rotation centre when the bucket foundations get the ultimate bearing state under pure moment load.The symmetrical H-M failure envelopes and fitted expression are established based on the numerical results.And the depths of the rotation centre and the fitted failure envelopes are used to optimise the expression of the traditional failure envelopes,so that all the parameters in the expression have corresponding physical meaning.(4)It is found that the interaction between the lid-soil with different tensions will affect the bearing capacities of the bucket foundation to a certain extent through the laboratory model test,and the proporties of the interaction mainly affect the antioverturning ultimate bearing capacity.According to the test results,the cohesive behavior is used in the numerical method to simulate the smooth and limited-tension interaction between the lid and the soil.The expressions of the uniaxial bearing capacities and V-H-M envelopes are obtained which can take into account the soil strength heterogeneity,the depth-diameter ratio of the bucket foundation and the maximum allowable tension of the lid-soil.