天津地区土动力学参数变异性对地表地震动参数的影响

Effect of Variability in Soil Dynamic Parameters on the Ground Motion Parameters of a Site Surface in the Tianjin Area

收集天津地区十多年来的83份地震安全性评价报告,统计202个钻孔的1 650组动三轴数据,分别给出不同种类土在不同区间深度下的统计代表值及其标准差。以某典型Ⅲ类场地为例,用等效线性化方法进行多种地震动强度及相位输入下的水平成层场地地震反应分析计算,详细研究该地区覆盖土层动剪模量比和阻尼比变异性对地表峰值加速度及其反应谱的影响。结果表明:场地地表峰值加速度和反应谱随土动剪切模量比增大或减小而增大或减小,随土动阻尼比增大或减小而减小或增大;在大震输入条件下,地表峰值加速度和地表反应谱的中、高频段随土动剪切模量比减小而减小的变化尤为明显,动阻尼比变化也有一定影响,但不如土动剪切模量比减小变化时影响明显;在中震、小震地震动输入条件下,场地土的动剪模量比和阻尼比变异性对地表峰值加速度和反应谱影响并不显著。

In recent years,seismic safety evaluation has been conducted at many engineering sites in the Tianjin area where dynamic nonlinear soil parameters can be obtained.In this study,we collected 83 seismic safety evaluation reports in this area and obtained 1 650 groups of dynamic triaxial data on soil from 202 boreholes.We then determined the representative values and their standard deviations of different types of soil at different intervals and different depths.A typical site Ⅲ is taken as an example.By using the equivalent linearization method to calculate the seismic response of the site under different ground motion intensities and phases,we studied in detail the influence of variability in the dynamic shear modulus ratio and damping ratio of the overlying soil on the peak ground acceleration and response spectrum of the site.The results show that the peak ground acceleration and ground response spectrum of the site increase or decrease with an increase or decrease,respectively,in the soil dynamic shear modulus ratio.However,the acceleration and spectrum increase or decrease with a decrease or increase,respectively,in the soil dynamic damping ratio.Under the input of a great earthquake,the soil dynamic shear modulus ratio decreases,and the peak ground acceleration and medium and high frequency portions of ground response spectrum decrease clearly.The change in the dynamic damping ratio also has a certain impact on peak ground acceleration and the ground response spectrum,but this is not as obvious as the change in the soil dynamic shear modulus ratio.Under the input of moderate and small earthquakes,variability in the soil dynamic shear modulus ratio and damping ratio have little impact on the peak ground motion acceleration and ground response spectrum.