Dynamic Response Characteristics Of Steel Screw Pile-soil Interaction Under Lateral Loadings

Due to its strong resistance to uplift,quick installation and load,reduced construction cost,adaptability to different soil conditions and short construction period,screw pile foundation is widely used in various civil engineering projects,such as transmission line engineering,pit wall and slope protection,offshore engineering and photovoltaic support foundation.In particular,it is pointed out that the long-distance operation of overhead transmission lines under a wide range of complex geological conditions and meteorological conditions,in addition to the uplift and downforce loads,the tower foundation suffers from wire tension,wind loads,wave loads and seismic loads.Under the action of horizontal loading,the dynamic interaction of the screw pile-soil system is more complicated and exhibits significant nonlinear characteristics.With the needs of national development strategies,many major projects have strict requirements on the vibration frequency and amplitude of the foundation,and the related experiments and theoretical research are not mature enough.Therefore,it is of great practical significance to study the vibration response characteristics of the steel screw pile foundation under horizontal dynamic loading.In this thesis,the steel screw pile foundation is taken as the main research object.Then a combination of theoretical analysis,finite element numerical simulation and model testing is used to study the nonlinear vibration response characteristics and pile-soil dynamic interaction of steel screw pile under horizontal loading.The main contents are as follows:(1)According to the principle of equivalent stiffness,the screw pile structure is equivalent to the pipe pile with the same inner diameter based on the equivalent stiffness method.Then the horizontal vibration model of the screw pile in equivalent single phase soil and saturated soil with pile-soil coupling system is established.Considering the soil boundary condition around pile and pile core,the horizontal vibration differential equation of the screw pile is solved by using the initial parameter method.The horizontal dynamic impedance of the screw pile at pile head is obtained.According to the existing research methods,engineering examples are added to visually describe the influence of pile structure parameters and main parameters of soil on the horizontal dynamic impedance of steel screw piles.(2)Using the sand box model test method,the self-made model test system of pile-soil dynamic interaction is made of three parts: the screw pile-soil system,the horizontal excitation system,the data acquisition and analysis system.The nonlinear vibration response characteristics of steel screw single pile and straight pile under horizontal excitation are studied.Then analyze the effects of length-to-diameter ratio,aspect ratio,sinusoidal load vibration frequency and excitation load amplitude on the horizontal vibration response of single pile.Based on the study of stress diffusion of soil around the screw pile,the interaction law of the steel screw pile and soil under the horizontal dynamic load is also given.(3)In order to further study the law of screw pile-soil interaction,a three-dimensional model of steel screw pile foundation was established.And modal analysis of screw pile-soil system was carried out by finite element method and ABAQUS software.Then,the dynamic response of the screw pile foundation under the action of horizontal sinusoidal load and horizontal seismic wave is studied.The results show that: with the increase of frequency,the horizontal displacement amplitude of the center point of the pile top gradually decreases;the acceleration of the screw pile foundation and the displacement of the pile top increase with the increase of the elastic modulus ratio of the screw pile to the soil.