Experimental Parameter Calibration And Application Of Sand Liquefaction Constitutive Model

Many UHV transmission steel towers are distributed on both sides of the Yangtze River,Yellow River,Huaihe River,Pearl River and other rivers,located in possible liquefaction sites,and have not been tested by strong earthquakes.Therefore,it is of great significance to study the effect of liquefaction caused by earthquake on UHV transmission tower.Sand liquefaction constitutive model is the core of numerical simulation of liquefaction site.Based on the results of the triaxial test and the numerical simulation software FLAC3D7.0,the physical significance,sensitivity and determination method of the parameters of the sand liquefaction constitutive model P2 PSand model were studied.The simulation results were compared with the existing shaking table test data,and the parameters of the constitutive model of Fujian standard sand were calibrated.Using the calibrated constitutive model parameters,the numerical simulation model of the transmission tower in the liquefaction site was established to study the dynamic response characteristics of the excess pore water pressure and acceleration at different depths,as well as the bending moment of the pile foundation and superstructure in the liquefaction site,which provided an important reference for the centrifugal shaking table model test design of the transmission tower.(1)A dynamic triaxial cyclic numerical simulation test of the constitutive model of P2 PSand based on FLAC3D7.0 software with the default model parameters(critical friction Angle φcs,plastic modulus coefficient h0,dilatancy Ad0,elasticity Gr,boundary coefficient nb,and dilatancy coefficient nd)as the basis.The effects of single parameters on axial strain ε and pore water pressure μ were analyzed by adjusting the variation of single parameters(±5%,±10% and ±20%).The results show that the sensitivity of φcs is the strongest,positively correlated with εand μ.The sensitivity of h0 is followed by that of h0,and with the increase of h0,the rise of ε and μ slows down obviously.Ad0 can promote the μ rising rate before liquefaction.The sensitivities of Gr and nb were weak,and nb inhibited the development ofεand μ before liquefaction.nd has little effect on ε and μ time histories.(2)Taking Fujian standard sand as an example,the significance of parameters of P2 PSand model was analyzed,and according to their sources,they were divided into two categories: parameters determined by experiment and parameters calibrated and fitted.The static parameters such as critical state parameters and elastic parameters were determined according to the results of triaxial compression test.According to the results of cyclic dynamic triaxial test,the parameters related to dynamic calibration and fitting were calibrated.The reliability of the calibrated constitutive model parameters is verified by applying the calibrated constitutive model parameters to the centrifugal shaking table model test of Fujian standard sand.(3)Using the calibrated constitutive model parameters,the numerical simulation model of FLAC3D7.0 for the transmission steel tower in the liquefaction site was established to study the dynamic response characteristics of the excess pore water pressure and acceleration at different depths,as well as the bending moment of pile foundation and superstructure in the liquefaction site.The results show that for pore pressure,the response inside pile group is faster than outside pile group,but the difference decreases with increasing depth.Compared with the input ground motion,the acceleration of soil mass has a certain amplification,but with the increase of pore water pressure of shallow soil mass,the effective stress decreases gradually,the soil stiffness decreases,the liquefaction phenomenon becomes more obvious,and the acceleration decreases gradually.In the substructure,the foundation soil has a certain lateral constraint on the pile foundation,and the maximum bending moment of the whole structure occurs in the upper structure.The results of this paper provide an important reference for the design and research of centrifugal shaking table model test of transmission tower in liquefaction site.