Research On Dynamic Response And P-Y Curve Regularity Of Group Piles In Liquefied Sand With Different Thickness

The lateral dynamic response of group piles in liquefied sand has always been a concern in the field of seismic engineering in geotechnical engineering.The lateral dynamic response of group piles and the interaction between piles and sand dynamics in liquefied sand under different ground motions need to be further studied.Based on the small electromagnetic shaking table test,this paper uses FLAC3 D to establish three-dimensional dynamic calculation models of straight group piles and inclined group piles in non-liquefied sand and different thickness liquefied sand,and compares the test results with the numerical analysis results to analyze the lateral dynamic response characteristics of group piles.On this basis,the variation of P-Y relationship curve of piles-sand dynamic interaction is analyzed.The main research work of this paper is as follows:(1)Carrying out small electromagnetic shaking table test research.Designing and manufacturing straight and inclined group piles models based on similarity theory.Obtaining the deformation data of piles body through FBG acquisition system,and then obtaining the relationship between piles-sand interaction force and displacement.Sine waves and seismic waves are input in the test.The sand model selects non-liquefied sand and liquefied sand with the thickness of 300 mm and 380 mm.Acceleration,displacement and pore water pressure sensors are deployed to obtain dynamic response data results.(2)Using the pre-processing software Midas-GTS NX to establish the three-dimensional model of the straight and inclined group piles and the division of the grid,then importing models into FLAC3 D.Determining the initial pore pressure field conditions and boundary conditions,and carrying out dynamic calculation.The comparison between the table and cap acceleration,displacement time history curve,data numerical simulation results and test results are carried out to verify the reasonableness of the three-dimensional numerical model.(3)Comparing the simulation results with the test results,the results show that whether they are straight group piles or inclined group piles,the acceleration and displacement peak of the piles cap amplification effect occur compared with the countertop.The magnifying effect in liquefied sand is obviously higher than that in non-liquefied sand,and the degree of enlargement becomes more significant with the increase of liquefied sand thickness.In addition,the magnifying effect of inclined group piles is significantly lower than that of straight group piles.Showing that the inclined group piles outperform the horizontal seismic load.Under the input of sine wave and seismic wave,the pore water pressure in liquefied sand starts to rise rapidly with the shaking input,and the pore pressure ratio exceeds 1.0,and the sand liquefaction occurs.The pore pressure ratio,acceleration and displacement of the countertop and cap are in good agreement with the experimental results,indicating that the acceleration,displacement and pore pressure ratio of the piles foundation are reasonable by using FLAC3 D.(4)The P-Y curve of the group piles was compared and analyzed in the non-liquefied sand and two different thicknesses of liquefied sand,the results show that the maximum lateral force,displacement and envelope area of the straight group piles are much larger than inclined group piles,showing that the energy consumption of the straight group piles during shaking is much higher than that of the inclined group piles.And the inclined group piles have a reduction effect on the lateral force.With the increase of liquefied sand thickness,the envelope area of P-Y curve increases,and the energy consumption of the piles also increases,and the lateral dynamic response of the piles becomes more significant.At the same time the main slope of the P-Y curve reduces,and the stiffness of the sand on the piles side reduces.The lateral force characteristics of the piles are affected by the depth of embedding.As the depth of embedding increases,the lateral force of the piles gradually reduces,the relative displacement between the sand and the piles gradually increases.