Seismic Response Analysis And Seismic Design Method Of Pile Foundation In Liquefaction-induced Lateral Spreading Ground

The design of foundation in liquefaction-induced lateral spreading ground during strong earthquakes is the key point and difficulty of the foundation design.The pile foundation is the primary choice for the foundation design in liquefaction-induced lateral spreading ground,which can sustain large lateral deformation of soil and has excellent seismic performance.However,the current research work mainly focus on the response of soil and pile during the earthquakes,the interaction behavior of soil-pile-superstructure is quite complicated and not clear,the guidance and theory of pile design is quite varied.On the above,the main object of this thesis is the problem of seismic and design of the pile foundation located in lateral spreading ground under strong earthquakes.First,the shaking table test and numerical calculation of pile foundation in the liquefaction-induced lateral spreading ground were conducted,and the typical dynamic response of piles under strong earthquakes was obtained.Then,the load transfer mode between soil and pile is discussed.After that,the phase relationship between the inertial load of pile and soil and th e crust load caused by lateral spreading is analyzed detailly.Last,the equivalent static design method of pile foundation in the liquefaction-induced lateral spreading ground which is based on the Beam on Nonlinear Winkler Foundation model is proposed.The main research contents of this thesis are as follows:1.Shaking table test of pile soil dynamic interaction under the effect of strong earthquake.Based on typical characteristics lateral spreading ground and the existing similar shaking test design experience,a shake-table test on a 2×2 pile group behind a quay wall was successfully implemented,and the time histories of pore pressure,acceleration and lateral displacement,and pile bending moments are discussed systematicly.2.The development of simplified analysis method for pile foundation of liquefaction-induced lateral spreading ground.The shaking table test based on the experimental results,A simplified analysis model was built based on the results of shaking table test,the connection stiffness between pile foundation and pile foundation and base is considered in this model,and the liquefaction-iuduced lateral pressure acting on the piles is obtained,and the difference of soil pressure is compared with the existing seismic design methods.Based on the simplified analysis model,the influence of pile diameter and stiffness of pile bottom stiffness on the response of pile foundation is analyzed.3.The numerical simulation of shaking table test is finished.In this thesis,based on Opensees finite element computing platform,numerical simulation for the completed pile-soil dynamic interaction shaking table test is carried out.The calculation platform,soil constitutive model,free water simulation,pile-soil interaction simulation and quay wall simulation are introduced in detail.The verification of the initial stress analysis of the model is conducted by drawing the initial stress field cloud picture(pore pressure,displacement and stress),and the correctness and reliability of the finite element model is verified by comparing the results of shaking table test with numerical calculation.4.The load transfer behavior and phase relationship between the inertial load and kinematic load of the pile-soil-superstructure system in the liquefaction-induced lateral spreading ground.The practical liquefaction-induced lateral spreading ground is idealized,and a typical seismic response model of the pile foundation in the liquefaction-induced lateral spreading ground is established.The load transfer behavior betewwn soil and pile is analyzed based on the results of finite element analysis.Parameter analysis on the soil-pile-superstructure system is conducted,the phase relation and load combination of inertial load and kinematic load are studied systematically.5.An equivalent static design method based on Beam on Nonlinear Winkler Foundation model is presented.The exsiting design method of pile foundation in lateral spreading ground is discussed firstly,then the equivalent static design method based on Beam on Nonlinear Winkler Foundation model is put forward,which solves three key problems,that is,the calculation of the inertia load of the superstructure of pile foundation under the condition of soil liquefaction;calculation of soil lateral displacement under given soil condition and ground motion in liquefiable ground.The inertia load of the structure and the method of the lateral displacement demand of the pile are determined.The general step of the method is given,and the design method is validated according to the dynamic nonlinear finite element analysis,at last,the design example of the pile seismic design in liquefaction-induced lateral spreading ground is given.