Research On Load-bearing Characteristics Of Large-diameter Rock-socketed Pile For Offshore Wind Turbines

With the large-scale consumption of fossil energy,it is imperative to develop clean and renewable energy.Monopile foundation is the most commonly used foundation form for offshore wind turbine.,which is driven into the seabed by hammer method and generally depth of mud entry is 40-60 m.It maintains stability by relying on the soil pressure on the side of the pile,and the top of the pile is connected with the fan tower cylinder,and the overall structure receives the combined action of wind waves and currents as a whole.Most of the southeast coastal areas of China are rock-foundation seabed,with overlying soft soil layer ranging from tens to tens of meters.In some areas,the soil resistance provided by soft soil layer is difficult to maintain the stability of the pile,so it is necessary to embed the pile foundation into the rock layer.At present,most of the built wind turbine foundations at home and abroad are located in the soft seabed,and there is little experience in designing rock-socketed piles.Therefore,it is necessary to study and analyze the load-bearing characteristics of rock-socketed piles.The main research contents and results of this paper are as follows:Taking the pile foundation with 5m outer diameter and 55 mm wall thickness as the research object,a 1:100 small scale model test design was carried out.The research on the experimental boundary effect shows that when the bottom boundary is larger than 3 times of pile diameter,the influence of the boundary can be ignored,and the experimental error caused by the lateral boundary at 8 times the pile diameter is within the acceptable range.Horizontal loading experiments were carried out on piles with different buried depths in sandy soil and rock-socketed conditions.The experimental results showed that under the same buried depth,the bearing capacity of the rocksocketed pile was larger,and the deeper the buried depth was,the more obvious the effect was.The experimental results are in good agreement with the simulation results of ABAQUS,and the results in the sand are basically in agreement with the prototype,which verifies the correctness of the experimental design hypothesis theory.The finite element software ABAQUS is used to calculate the deformation behavior of a single pile foundation under the ultimate load in a certain area of Fujian.The pile deformation,bending moment and shear force distribution are compared and analyzed.When the depth of rock-socketed pile is close to 2 times of pile diameter,increasing the buried depth has no effect on the bearing characteristics of the pile.The passive soil pressure of rock layer plays an important role in maintaining the stability of pile,and the overlying soft soil layer also plays a certain role.After grouting around the pile,the bearing capacity has been improved.There are three failure zones in the grouting layer under the ultimate load.The strength of grouting material has little effect on the bearing capacity,and increasing the thickness of grouting material can significantly improve the bearing capacity.