深厚软弱场地地震反应特性研究

以南京、盐城、上海的 3个典型场地作为长江下游地区深厚软弱场地的代表 ,探讨了深厚软弱场地的地震效应特性。首先 ,利用南京工业大学岩土工程研究所自行研制的GZZ 1自振柱试验机 ,对 3个典型场地的原状土样进行试验研究 ,获得了各类典型土的动剪切模量和阻尼比随剪应变的变化曲线 ;其次 ,选用Taft、ElCentro和Northridge地震记录作为输入地震动 ,将Taft、ElCentro和Northridge地震波加速度时程的峰值水平调整为 0 .35m/s2 ,0 .70m/s2和 0 .98m/s2 ,利用程序SHAKE91对 3个场地进行了输入不同地震波、不同峰值加速度水平的 2 7种组合的地震反应分析。数值分析表明 :场地条件和基岩输入地震动特性对土层的地震加速度放大效应有显著影响 ,地表处的地震加速度放大系数随着输入地震波峰值的增加而减小 ,土层内部的这种规律性不如地表处表现得明显 ;地表软弱土的存在使土层地表处的地震加速度放大系数急剧增大 ,场地内部软弱土夹层处的地震加速度放大系数急剧增大 ,强震时易失效 ;互层土特殊的层理构造会造成该土层的剪应变幅值急剧增大。

Research on Seismic Response Characteristics of Sites with Deep and Soft Soils

To research seismic response characteristics of sites with deep and soft soils, three typical sites from Nanjing?Yancheng and Shanghai are selected and analysed respectively in the paper. At first, making use of model GZZ-1 free vibration column test system, the authors do the experiment on the undisturbed soil samples from the three sites, and the curves of dynamic shear modulus ratio G/G_(max) and damping ratio λ versus dynamic strain amplitude γ for all sorts of soils are attained. Secondly, utilizing SHAKE91 program, the seismic response characteristic of three sites is obtained. In the paper, Taft earthquake wave?El Centro earthquake wave and Northridge earthquake wave are regarded as input waves, and their peak acceleration is adjusted to 0.35 m/s~2 ?0.70 m/s~2 and 0.98 m/s~2. So the paper analyses site seismic effect of 27 cases. Through the numerical analysis of all sites, the following can be concluded: the factor as site condition and the characteristic of input wave have an obvious impact on ground surface acceleration amplifing effect of soil strata, the less the ground surface acceleration amplification factor, the larger the peak value of input acceleration time-history is, but this regulation is not obvious for inside soil strata; the ground surface acceleration amplification factor will increase quickly when there is soft strata at the ground surface; the ground surface acceleration amplification factor at soft mucky soil is relatively bigger than other soil strata ,and this strata is easily destructed under strong motion; shear strain of the interbedded strata will be bigger because of its particular layer construction.