土参数对表面波有效相速度影响

Effects of soil parameters on effective phase velocity of surface waves

本文利用薄层刚度矩阵法计算模态频散曲线及表面质点竖直向振动有效相速度,分析了几种典型层状介质的土层参数变化对模态频散及有效相速度影响。结果表明:模态频散及有效相速度对泊松比变化较敏感,密度、阻尼比变化对模态频散及有效相速度影响可以忽略,由模态频散或有效相速度数据分析土层剪切波速时,可以事先设定土密度及阻尼,预设值对分析结果影响不大;高阶模态比基阶模态对深层剪切波速变化敏感,结合高阶模态频散分析,可以减少分析结果不确定性;表面波有效相速度主要受其波长深度内各层土参数影响,深度超过一个波长各层剪切波速分析结果不确定性较高。

The dispersions of the modes and the effective phase velocity of surface waves in layered soil media are related to the shear wave velocities,Poisson’s ratios,densities and damping ratios of soils.The shear wave velocity profiles of soils can be attained by analyzing the dispersions or the effective phase velocities obtained from the surface wave testing.The dispersions of the modes and the effective phase velocities of vertical vibrations of surface waves are calculated based on the thin layer stiffness matrix method.Effects of soil parameters on the dispersions and the effective phase velocity are investigated for several typical layered soil media.The results show that the dispersions and the effective phase velocity are sensitive to variation of Poisson’s ratio,while effects of variation of the density and the damping ratio on the dispersions and the effective phase velocity can be ignored.This indicates that the densities and the damping ratios of soils can be initially given in back analysis and the variations of these parameters have little influence on the calculated shear wave velocity profiles.The higher modes are more sensitive to variation of the shear wave velocities of deeper soils than the lower modes.The non-uniqueness of results can be reduced by combining analysis of the dispersions of the higher modes.The effective phase velocity is mainly controlled by the parameters of soils within the depth of about one wavelength.The shear wave velocities of soils beyond one wavelength can not be effectively determined.