Study On The Influence Of Seismic Frequency On Sand Liquefaction

Sand liquefaction has been an important issue in geotechnical engineering research.Many disasters caused by sand liquefaction,such as the ground instability,the building collapses,the ground sand blasting,and the foundation settlement,will result in incalculable losses for the people's lives,property and spiritual life.Among the seven factors affecting sand liquefaction,the influence of frequency on the liquefaction of sand has been explored by many researchers in recent years,however,some different conclusions and results have been drawn among them.Furthermore,the study on the effect of different seismic frequencies on the liquefaction of sand under the same acceleration condition is still in a blank stage.Therefore,based on the same seismic acceleration condition,the influence of seismic frequency ranged of 2~10Hz on sand liquefaction was studied in details.In this paper,a combination of shaking table test and FLAC3D(Fast Lagrangian Analysis of Continua)numerical simulation was used to analyze the influence of the different seismic frequency on sand liquefaction from the aspects of excess pore water pressure,pore pressure ratio,liquefaction macroscopic phenomena,and liquefaction ground subsidence.The experimental results show that under the same earthquake acceleration conditions;the macroscopic phenomena of sand liquefaction under different seismic frequencies are different.The larger the seismic frequency is,the more clear the water and the less foam appears on the surface of the model foundation after liquefaction,and the longer the time from the pre-vibration state to the fluidization state of the model foundation is.After the liquefaction,the settlement of the surface of the model foundation gradually decreases with the increase of the frequency,and the curve of “subsidence-frequency” is well fitted,By modifying the existing formula for the growth of the excess pore water pressure,the formula for excess pore water pressure increase under shaking table test conditions is given,Among the range of 2~10Hz,there exists a “critical frequency” with the increase of frequency,which makes the liquefaction state of the model foundation change from “complete liquefaction” to “partial liquefaction”,even to "non-liquefaction" finally.The numerical calculation results show that the excess pore water pressures are different with the change of seismic frequencies,but all are consistent with the basic growth law that the deeper the depth is,the greater the value of the excess pore water pressure is;It is found that the ground surface settlement is gradually decreased with increasing frequency from 2 to 10 Hz.There is also a “critical frequency” with the increase of the frequency,in which the value of the pore pressure ratio began to change from being in the liquefaction range to the non-liquefaction range.All of the results in this thesis will be helpful for understanding of sand liquefaction,and will also provide a theoretical basis for the relative engineering application.