Effects of soil parameters on effective phase velocity of surface waves

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.