Analysis Of Steel Pipe Pile Dynamic Characteristics Under Scour Conditon

Steel pipe pile foundation is widely used in the design of cross-sea bridge,harbor and offshore wind turbine foundation,in the near shore,deep sea harsh environment,steel pipe pile foundation bears a lot of wind,waves and other dynamic lateral load,it's difficult to guarantee foundation's dynamic stability;At the same time,under the action of the wave load,scouring phenomenon surrounding the pile bottom proposes higher requirements for long-term stability of the structure,if poorly considered,the system will lead to dynamic destruction.Therefore,it is of great practical significance to study the dynamic characteristics of steel pipe pile foundation under scouring.Based on the project of National Key Basic Research and Development Program(No.203CB036304)and the Basic Research Project of Ministry of Transport(No.2013319759060),this paper takes the H1#100MW offshore wind farm in Jiangsu Province as engineering background,main research contents are as follows:Two theories related to scouring calculation are introduced:scouring theory and wave theory.On the basis of relevant theory,combined with the relevant hydrological and geological data of H1#offshore wind farm project,the wave load and the local scouring depth interval condition are calculated under the extreme working condition,then,Airy wave theory is selected to calculate the overall wave force,because it's the most convenient and effective method.Combined with the vibration response equation of pile foundation,a p-y curve considering the size of the scouring hole is proposed to describe the horizontal resistance of soil.New p-y curve can analyzes and simulates the horizontal resistance of soil better after scouring.A frequency calculation numerical model is established and applied to a full scale field test.The results show that:(1)The equivalent scour depth calculation method is convenient and effective;(2)The method of simulating soil erosion as the absence of soil spring and reduction of the overall stiffness matrix is feasible.To study the effect of scouring and dynamic characteristics,two steel pipe pile foundation model test were designed:wave tank test and dynamic parameter test.Three scouring depth were considered:0 cm,15cm and 30cm;three depth of water were considered:25cm;35cm,45cm.Then,ABAQUS finite element software was used to simulate the same model,vibration frequency,vibration accleration,vibration displacement and other dynamic response were compared.Dynamic test mainly studied the dynamic parameters of steel pipe pile foundation under different scouring depth,such as resonant frequency,horizontal shear stiffness,horizontal shear stiffness coefficient,first vibration damping ratio and vibrational vibration mass.Whole model of offore wind turbine is established by ABAQUS.The theory of dynamic control design is given.Tempel simplified formula and Block Lanzcos method are used to analyze and compare the frequency change under different scour depth.Finally,the dynamic response of the steel pipe pile under the wave load after the equivalent depth is obtained,and some meaningful conclusions are drawn.