淤泥质软弱表土对场地地震反应的影响

Effects of muddy soft topsoil on seismic response of sites

以2个简化的场地为原型,将不同厚度淤泥质软弱土层置于场地表层构造了多种土层反应分析模型。采用等效线性化方法和非线性地震反应方法分别对其在3种输入地震动强度下进行地震反应分析。当采用等效线性化方法进行地震反应时,随着软弱表层厚度的增加,加速反应谱特征周期逐渐增大,而峰值加速度则先增大后减小。对于含较厚软弱表层的场地,在较强地震动作用下,等效线性化方法会造成地表反应谱高频成分被严重低估,而去除软弱表层会使得反应谱特征周期偏小。而非线性地震反应方法可以避免这种误估,故对含厚淤泥质软弱表层的场地建议使用非线性计算方法。当场地软弱表层厚度有限时,等效线性化方法得到去除和保留软弱表层的场地加速度反应谱结果相差甚小,此时可选择更为简便的等效线性化方法进行地震反应分析。

Two simplified sites are set as the original models,based on which a variety of studied models are constructed by placing muddy soft soil with different thicknesses on the top of the original models. Then equivalent linearization method and nonlinear seismic response method are utilized to study effects of muddy soft topsoil on seismic response of sites at three intensities of input motion. If the equivalent linearization method is used for seismic response,with the increase of the thickness of the soft surface,the characteristic period of the acceleration response spectrum gradually increases,while the peak acceleration first increases and then decreases. For sites with thick soft topsoil,the equivalent linearization method makes the high frequency components of the surface response spectra to be seriously underestimated at strong earthquake,while the removal of the soft topsoil makes the characteristic period of the acceleration response spectrum underestimated. The nonlinear seismic response method can avoid such misjudgment,so it is recommended to use nonlinear method for sites with thick muddy soft topsoil. When the thickness of the soft surface layer is quite limited,there is little difference between acceleration response spectra of sites with the soft topsoil removed or retained,and the convenient equivalent linearization method can be chosen for seismic response analysis in this case.