| With the large-scale development of new energy sources,the development of offshore wind power has gradually attracted widespread attention.Bucket foundation is a new type of offshore wind turbine foundation and in the shape of an inverted cylinder,with a closed top and an open bottom.There is a large amount of soft clay in the offshore area in China.The high compressibility and water content will cause uneven settlement of the soil inside the bucket foundation,which is disadvantageous to the operation of the wind turbine.Therefore,it is necessary to consolidate the soil in advance to improve the bearing capacity of the foundation.After the bucket foundation is air hauled to the designated location and sunken into the soil by means of negative pressure,it is convenient to reinforce the soil inside bucket by using the vacuum preloading method to improve the bearing capacity and stability of the bucket foundation.In order to further improve the reinforcement effect,this paper also puts forward the vacuum preloading combined with electro-osmosis method to strengthen the bucket foundation.The main research contents and results are as following:The reinforcement tests in the cohesive soil are carried out with the bucket model with an outer diameter of 30 cm and a clear wall height of 12 cm,without bulkheads inside,including four schemes by vacuum preloading method and vacuum preloading combined with electro-osmosis method,and the effect of reinforcement are analyzed.The test results reveal that the consolidation effect is more under combined reinforcement method,and the variation of soil moisture content and strength after reinforcement decreases with the increase of depth.Electro-osmosis electrode plays the role of negative transfer,thus increasing the degree of soil consolidation.The higher energy utilization rate and better reinforcement effect can be reached when steel bucket wall is taken as cathode,and the reinforcement effect decreases with increasing distance from the anode,but there is poor uniformity of soil in the depth direction.The soil resistance is uneven and larger near the electrode,as a result,electrode layout will affect the distribution and trend of soil potential in the process of electro-osmosis.The results of the model test are compared with the finite element software ABAQUS,and the validity of the numerical simulation method is verified.At the same time,a three-dimensional numerical model is applied to simulate the consolidation process of soil for bucket foundations with and without bulkheads,and to analyse.This paper investigates the reinforcement effect of the two foundation types to assess the influence of the bulkheads.The results obtained show that there are obvious reinforcement effects for both foundation types.In the early stage of consolidation,vertical settlement is rapid and this becomes stable with time.The depth at which the pore water pressure becomes negative is the depth showing the main reinforcement.Vacuum pressure decreases continuously with increase in soil depth and time.In addition,the excess pore water pressure in the soil dissipates,which turns into the soil effective stress.Bulkheads provide vertical drainage channels in the soil and shorten the seepage path,allowing the extraction of more pore water.This is conducive to the improvement of shallow soil,while also decreasing the extraction of pore water in deep soil and the region of the soil that can be reinforced. |
