软土层几何特性与剪切波速对场地峰值加速度的影响

Influence of the Geometric Properties and Shear Wave Velocity of a Soft Soil Layer on the PGA Response of Site

软土层对场地地震动的影响一直以来是地震工程学的研究重点。本文应用一维真非线性场地反应分析方法,对某单层匀质场地内软土层的几何特征(厚度与埋深)和剪切波速变化对地面峰值加速度的影响进行了数值分析。研究结果表明:软土层的存在使得场地加速度幅值分布在软土层处发生突变,随着软土层几何特性和剪切波速的不同,这种突变可能使得地面峰值加速度增大或减小;存在一个由软土层厚度、埋深和相对剪切波速三个参数构成的临界状态面,当软土层的状态位于临界面以内时,软土层对地面峰值加速度起放大效应,且加速度效应系数随着上述三个变量的增大表现出先增大后减小的变化规律;当软土层位于临界面以外时,其对地面峰值加速度起衰减效应,加速度效应系数随着上述三个变量的增大而减小。根据算例的参数分析建立了其临界面方程,并提出了估计软土层加速度效应系数的经验公式,可为类似问题提供参考。

The earthquake response of soil deposits containing a soft layer has been of great interest in geotechnical earthquake engineering practice. This paper introduces a study on the influence of a soft layer on the ground motions of a homogeneous deposit, with the variation of geometric properties and shear wave velocity of the soft layer. Numerical studies are conducted by method of real nonlinear one dimensional site response analysis. Results indicate that the existence of a soft soil layer in the deposit will cause sudden change of the acceleration response in the profile, and the PGA may be increased or decreased based on the geometric properties and shear wave velocity of the soft soil. There exists a critical range as which being exceeded the PGA will be decreased monotonically with the increase of the soft soil's thickness, buried depth and relative shear wave velocity. On the contrary, as the critical range is not exceeded, the PGA will be enlarged in a trend of decreasing after increasing with the increase of the soft soil's thickness, buried depth and relative shear wave velocity. Formula describing the critical range and empirical methods estimating effects of a soft soil layer on PGA are proposed based on parametric analysis of a homogeneous site. Reasonability of proposed method is validated by numerical calculation results. Foundations of this study may provide reference for further research and application.