Study On Dynamic Response Of Pile Group Foundation Om Liquefiable Ground Based On The Shaking Table Test

Pile group foundation could better adapt into a variety of complex geological conditions and suffer different load conditions.It is of high bearing capacity,low settlement and great stability characteristic.It is one of the basic forms that are widely used in high-rise buildings.However,during earthquake disasters with severe earthquake damage worldwide,the pile foundation in the liquefiable ground was severely damaged,which led to the collapse of houses,bridges and lifeline engineering.The dynamic response of the pile group foundation on the liquefiable ground has become one of the research hotspots in the field of earthquake resistance in geotechnical engineering.The study on the dynamic response of the pile group foundation on the liquefiable ground is of great significance to the seismic design and disaster prevention and reduction of pile foundation on liquefiable ground.In this paper,through the investigation of earthquake damages in several major earthquakes and the summary of the failure mechanism of pile foundations,some useful experiences and enlightenments are obtained,which provide experience for the seismic analysis and experimental research of pile foundations on liquefiable ground.In addition,based on a high-rise building structure pile group system on the liquefiable ground,a similar theory was used to design the shaking table test model.A 1/50 liquefiable ground—group pile—superstructure dynamic interaction system shaking table test was conducted to study the dynamic response characteristics of liquefiable ground and pile group foundation.Besides,Open Sees finite element seismic simulation platform is used to supplement the numerical simulation calculation,and the deformation law of pile-soil under liquefaction condition is deeply analyzed.The main research work and corresponding results of this paper including:(1)Aiming at the problem of failure of pile foundation on liquefiable ground,the causes of failure of pile foundation on liquefaction foundation are explained in detail by starting from the location of failure of pile foundation on liquefiable ground foundation and mechanism of failure after earthquake.As for the design of the pile foundation on the liquefiable foundation,it is necessary to consider the analysis of the pile-soil-structure dynamic interaction and superstructure should be regarded as a whole.(2)In order to explore the dynamic response law of pile group foundation on liquefiable foundation,based on a pile group system of a high-rise building structure as the prototype,the shaking table model test of 1/50 scale liquefiable site — pile group — superstructure dynamic interaction system was conducted.The dynamic response law of the liquefiable site and pile group foundation under the excitation of different types and different directions of seismic waves has been studied.The results show that the degree of liquefaction of saturated sand is related to the type of input seismic wave and the interaction of horizontal and vertical earthquakes.With the increase of the peak acceleration,the damage of pile foundation becomes more serious.In addition,the combined action of horizontal and vertical earthquakes not only increases the damage in the middle and bottom of pile,but also causes the rotation effect of pile group foundation obviously.Compared with the horizontal seismic action,the horizontal and vertical seismic action aggravated the sway and tilt of the liquefiable pile group foundation during the earthquake,which caused serious damage to the building.For the design of pile foundation on liquefiable foundation,it is suggested to consider the adverse effect of both horizontal and vertical earthquakes.(3)Based on the shaking table test and Open Sees finite element seismic simulation platform,a nonlinear three-dimensional numerical analysis model of the dynamic interaction system of liquefiable ground and pile group foundation is established.During building the model,the selection of soil material constitutive,the determination of pile-soil connection,meshing and the simulation of boundary conditions are considered.By comparing with the test results,the accuracy of the finite element numerical model is verified,which could provide an effective supplement to the shaking table model test.(4)According to the finite element numerical calculation model and the analysis of the test data,the deformation law of pile-soil under liquefaction conditions is obtained.The analysis results show that with the increase of the peak acceleration of the input wave,the excess pore water pressure of the liquefiable sand layer increases significantly,but after the soil is completely liquefied,the increase in seismic action has little effect on the increase of the pore water pressure of the soil.Due to the lateral flow of the soil foundation during the liquefaction of sand,there is still some residual bending moment in the pile foundation after the earthquake.In addition,the bending moment of the pile body presents a distribution rule of large at the top pile and small at the bottom pile.For the pile foundation design of the building structure on the liquefiable foundation,the pile strength at the pile head should be considered.This paper could greatly enriche the research on the dynamic response of pile groups on liquefiable foundations.It is of great significance for the design of pile foundations of buildings on liquefiable sites and disaster prevention and mitigation.Also,it could be used for earthquake resistance of pile foundations on subsequent liquefied foundations and provide important reference for the subsequent seismic analysis of pile foundation on liquefiable ground.