Study On Site Response Of American Wildlife Liquefaction Array

The American Wildlife Liquefaction Array(WLA),located in a highly seismicity active area by the southernmost part of San Andreas fault,south California,America,is mainly used for research on sand liquefaction.Since being built by USGS in 1982,WLA captured the acceleration and pore pressure time histories of Superstition Hills(SSH)earthquake in the year of 1987,which has been proven of severe liquefaction by seismic damage investigation.During 2003 to 2004,researchers of NEES reconstructed WLA from when the new WLA had been in usage till now.In this paper,acceleration time histories of 180 earthquakes recorded by WLA from the year of 2004 to 2013 are processed and corrected firstly.Then make use of corrected acceleration records of 146 earthquakes to analyze characteristics of linear and nonlinear site response,with horizontal-to-vertical spectral ratios(HVSR)method.Based on acceleration and pore pressure data recorded in the SSH earthquake,explore the features of three essentials of ground motion and soil dynamic parameters of WLA when it underwent significant liquefaction.Ultimately,identify the sand liquefaction possibility in 146 earthquakes of WLA according to three liquefaction identification methods,compare three essentials of ground motion in the earthquake identified of possibly liquefaction with SSH earthquake,estimate the determinacy of its liquefaction.Results indicate that:1.172 out of 180 earthquakes with intact acceleration data are baseline-corrected and filtered,leading to 146 earthquakes with valid ground motion records.Except for 90 earthquakes with peak ground acceleration(PGA)smaller than 20cm/s2.other 56 events,among which 8 earthquakes with P(iA ranging from 100 to 200cm/s2 and 2 with PGA greater than 200cm/s2.are also included.2.In the upper 30m soil layers,the HVSR curves for east-west and north-south direction of WLA keep the same characteristics,which show little anisotropy.For the same earthquake,the fundamental frequency doesn't change with growing depth.For different earthquakes,the fundamental frequency decreases when PGA is greater than 100cm/s2,which show obvious nonlinear site response,therefore the limit of nonlinear response.100cn/s2.is concluded.In 2 directions.amplification factors corresponding to fundamental frequency turn out linear increasing with decreasing depth.And for different earthquakes,the amplification factors hardly show any rules.3.The peak ground acceleration,velocity and displacement for SSH earthquake is 201cm/s2,30cm/s.12cm respectivelxy.Low frequency vibration appears in the middle and final segment of acceleration history with amplitude of half of PGA.In frequency domain,the ground motion energy focus on 0.2?2Hz and hold same features in 2 directions.While the bracket duration and uniform duration differ obviously at the surface.At 2.9m underground,excess pore pressure ratio reach 50%since 20st second,the ascent of pore pressure leads to decline of stiffness and strength manifesting by small shear stress along with much bigger shear strain.Pore pressure decreases temporally when shear strain comes to its peak.4.According to three sand liquefaction identification methods(Suzuki,Ozaki,Miyajima method),in SSH earthquake,WLA turns out liquefaction,in No.13740 earthquake possibly liquefaction,and others non-liquefaction.Compared with records of SSH earthquake,none low-frequency vibration appears in the final segment of acceleration history in No.13740 earthquake,the amplitude and distribution of Fourier spectral in frequency domain differ much with the former.And each duration is far smaller than SSH earthquake.In conclusion,WLA turns out non-liquefaction in No.13740 earthquake.