Factors Influencing Iiquefaction Sites Under Horizontal Seismic Action Research

Liquefaction of sand is an important factor that causes damage to geostructures and earthquake and geological disasters.The factors causing sand liquefaction can be classified into two categories: site conditions and ground motion,and abundant research results have been obtained.However,the systematic understanding of site conditions,ground motion input and seismic response parameters(surface subsidence,acceleration amplification effect,shear strain and pore pressure ratio)is still insufficient.In this paper,the open source software OPENSEES is adopted to study the influence of PDMY02 elastoplastic constitutive model on liquefaction effect from three dimensions: soil layer structure characteristics,soil parameters and ground motion input.The main work and results of this paper are as follows:1.The influence of soil layer structure characteristics(buried depth of liquefied soil layer,inclined slope of liquefied soil layer and groundwater level)on seismic response of liquefied site is studied.The following rules are obtained:(1)With the increase of buried depth of liquefied soil layer,surface seismic subsidence first increases and then decreases;The surface acceleration amplification coefficient R decreases first and then increases.The maximum shear strain of the liquefiable soil layer reaches its maximum value in a certain buried depth.(2)As the slope of the site increases,the surface amplification factor R shows an increasing trend,the surface subsidence increases in a certain slope area,and the site’s excess pore water pressure increases to a certain extent compared with the peak value.(3)With the increase of the depth of the groundwater table,the surface subsidence decreases,the surface acceleration amplification coefficient R increases,and the shear strain of the soil layer in the middle of the site is greatly affected by it.2.Based on a liquefaction site model,500 groups of parameters were selected and input into the site model by Latin Cube sampling technique,considering the randomness of soil density,shear modulus and internal friction Angle.The seismic response parameters of liquefaction site under the action of two seismic waves were calculated,and the probability distribution characteristics and probability characteristic values of the response quantity of liquefaction site were calculated.The normalized method and tornado diagram method were used to order the size of soil property parameters which affected the reaction quantity of liquefaction site respectively.The following rules were obtained:(1)The distribution characteristics of surface acceleration amplification coefficient R and surface subsidence value were in line with lognormal distribution,while the distribution characteristics of maximum shear strain value of soil layer in the site were in line with normal distribution.(2)The maximum shear strain of soil layer is most susceptible to the variability of these six soil property parameters,followed by the surface acceleration amplification coefficient,and finally the surface subsidence.(3)The order of sensitivity of a single reaction quantity to soil property parameters is as follows: a)Taking surface acceleration amplification coefficient R as the target: friction Angle of loose sand layer > shear modulus of dense sand layer > shear modulus of loose sand layer > density of loose sand > density of dense sand > internal friction Angle of dense sand.b)Taking the seismic subsidence of the site as the target: shear modulus of the liquefiable soil layer > friction Angle of the liquefiable soil layer > dense soil layer > shear modulus of the dense sand layer > dense sand density > friction Angle of the dense sand.c)Take the maximum shear strain of soil layer in the site as the target:friction Angle in the liquefiable soil layer > density of the liquefiable soil layer > shear modulus of the liquefiable soil layer > density of dense sand > friction Angle in dense sand > shear modulus of dense sand.3.The influence law of the peak value and spectral characteristics of the input ground motion on the seismic response parameters of the liquefaction site is studied,and the law is as follows:(1)the influence of ground motion amplitude: the variation function of ground motion amplitude of ground subsidence is an approximate quadratic function;The surface amplification coefficient R showed a downward trend in the range of [0.2g,0.3g].The peak value of excess pore water pressure at each depth of the site changed most obviously in the interval [0.05 g,0.2g],and the duration increased significantly in the interval [0.2g,0.3g].(2)Influence of ground motion frequency: surface subsidence and surface acceleration amplification coefficient R reach the maximum value when approaching the natural vibration frequency of the site,and surface subsidence is most sensitive to the change of low frequency waves.After a certain frequency is exceeded,the surface subsidence has a slow downward trend.When approaching the natural vibration frequency of the site,the duration of the excess pore water pressure in the upper soil layer of the site will be significantly longer than the peak value.(3)Influence of seismic wave waveform: surface subsidence is greatly affected by waveform,surface acceleration amplification coefficient R is little affected by waveform,and the time history curve of excess pore water pressure ratio in the upper soil layer of the site is most easily affected by waveform.The results obtained in this thesis provide an important reference for the seismic design of liquefaction sites.