Preliminary Study On Liquefaction Discrimination Method Of Sandy Soil Based On Microtremor

Sand liquefaction is a geological disaster caused by strong destructive earthquakes,which is one of the main reasons for foundation failure and engineering structure damage.It is an effective means to reduce the liquefaction disaster of sandy soil by evaluating the liquefaction trend of the site and proposing anti-liquefaction measures through the liquefaction discrimination method.Therefore,the research on liquefaction site discrimination method has been the concern of researchers.Microtremor can reflect the soil structure information of the site.It is an economical,convenient and efficient method for testing the dynamic characteristics of the site.It is widely used in seismic damage analysis,building structure design,site classification and site evaluation.Taking Songyuan Ms5.7 sandy soil liquefaction site as the research object,by means of field investigation,Microtremor and theoretical analysis,the influence law of sandy soil liquefaction on-site dynamic response and its excellent frequency is revealed,and the feasibility of applying Microtremor technology to liquefaction site discrimination is verified.The method of the field test,data analysis and processing of Microtremor in liquefaction site,liquefaction site and the construction site of sandy soil liquefaction discrimination are given,which provides basic research data for regional discrimination of sandy soil liquefaction and enriches the engineering method of earthquake prevention and disaster reduction.The following research results are obtained in this paper :(1)The theory of Microtremor measurement is briefly introduced,and the data processing method of Microtremor is explored.In this paper,the anti-STA/LTA algorithm is applied to the Microtremor data to intercept the stationary data segment,so as to eliminate the pulse signal interference.The results show that when the anti-ST STA/LTA algorithm is applied,the short-time window is set to 2s,the long-time window is set to 20.48 s,and the threshold is set to 2.5,the data of Microtremor processing can achieve the effect of eliminating pulse signals.At the same time,the single-point spectral ratio method is used to process the Microtremor signal in each time window.The calculation method,smoothing mode and smoothness of the horizontal component in the single-point spectral ratio method are also explored.The results show that the horizontal component calculation method adopts the square root method,the smoothing mode is selected as the Hanning window,and the 0.8Hz smoothing filtering can achieve better Microtremor processing effect.(2)Based on the Microtremor test results of sandy soil liquefaction in Songyuan Ms 5.7 earthquake,a method for judging sandy soil liquefaction by ground pulsation is proposed.26 free sites and survey lines along the Songhua River were selected to collect data of Microtremor.Among them,14 sites were liquefied ejection sites,7 sites were non-liquefied sites,and 5 sites were liquefied non-ejected sites.The single point spectral ratio method is used to analyze the data of Microtremor,and the characteristics of Microtremor between liquefied site and non-liquefied site are compared and analyzed.The results show that after the earthquake,Vulnerability Indices of Ground(Kg-value)calculated by the single-point spectral ratio method of Microtremor test data decreases significantly,and Vulnerability Indices of Ground(Kg-value)is less than 5,while the liquefaction site increases.On this basis,the Microtremor test method for sandy soil liquefaction is proposed: the Microtremor test is carried out on the site of the first terrace in Songyuan area,and the single point spectral ratio method is used to process the data to calculate whether the Kg-value is greater than 5 as the basis for judging whether the site is a liquefaction site.It provides new methods and new ideas for whether sand liquefaction occurs in the site.(3)Based on the earthquake prevention and disaster reduction planning project of Songyuan City,the borehole data of 19 sites were collected as the research basis to verify the proposed method for distinguishing sand liquefaction based on the data of Microtremor.The standard penetration method was used to discriminate sand liquefaction in 19 sites,and 7 sites were easily liquefied.At the same time,19 sites were tested for Microtremor.At the same time,the Microtremor test method is used to calculate Vulnerability Indices of Ground(Kg-value)of each site by single point spectral ratio method to judge the liquefaction of sand.Taking the standard penetration method as a reference,the accuracy of the Microtremor test for liquefaction discrimination of site sand is verified.The results show that in Songyuan area,the success rate of sand liquefaction discrimination in the first terrace is 60%;The success rate of sand liquefaction discrimination in the secondary terrace is 66.7%.