砂土液化对设计反应谱和场地分类的影响

Effect of soil liquefaction on design response spectrum and site classification

本文采用有效应力原理分析了液化土层对设计反应谱的影响,分析中考虑了砂层的厚度、埋深和输入地震动等因素。选择Ⅱ类场地,将其标准反应谱合成的三条地震加速度时程在考虑土层非液化下反演到基岩,再正演计算存在液化层时的地面运动时程和反应谱。分析结果表明,从特征周期的变化来看,液化土层使Ⅱ类场地易变为Ⅳ类场地,对地震影响系数的作用则不是很大,但频谱上0.8s是一个分界线,液化土层对分界线以下的高频分量有一定减震效果,对分界线以上的低频分量有显著的放大效应。

This paper presents the effects of soil liquefaction on design response spectrum in terms of effective stress theory by considering the thickness and depth of sand layer, and the earthquake intensity. For the type Ⅱ site, three artificial seismic acceleration time histories from the standard design response spectrum are inversed to the bedrock and taken as input waves when the soil layer is refersed to a nonliquefaction site. Then the surface ground motion is calculated by the presented method in case of the liquefiable soil layer. The results imply that the type Ⅱ site is easily turned to the type Ⅳ site from the view of characteristic period due to the sand liquefaction, but the earthquake influence factor is not changed greatly. The 0.8s in the spectrum may be a boundary point, below which the liquefied soil layer decreases the vibration in a certain degree and beyond which the liquefied soil layer greatly increases the amplitude of the surface motion.