The Spectral Analysis of Surface Waves (SASW) method has a great potential for rapid determination of shear wave velocity profile of the ground. However, there are few studies on the cases of the inclined soil layer because it is much more difficult to obtain analytical solutions of wave propagation than in the horizontal layer. Therefore, the numerical study is required as an alternative to verify the characteristics of wave propagation in the inclined soil layer.
In this study, a finite-element computer code, ABAQUS, has been employed to simulate the SASW method. By performing the optimization study of finite-element size in the horizontal layer, it was found that the sampling rate is an important factor and the ratio of element size to the shortest wavelength of interest should be less than 0.1. The numerical dispersion curves were compared with the theoretical dispersion curves to verify the optimization of mesh size. Then, the effects of dip and testing direction on the experimental dispersion curve were investigated in the inclined layer where the bottom layer was stiff. Total of 26 cases of numerical studies were performed to accomplish this task. The results indicate that the influence of the dip on the dispersion curve increases obviously as the dip angle increases. The fluctuation of surface wave velocity was observed due to the presence of the inclined interface of the different stiffness and the fluctuation becomes more severe as the stiffness contrast increases. Contrast to the general knowledge, the surface wave velocity determined by the forward testing, where wave propagates from the deep interface to the shallow interface, was faster than that determined by reverse testing at the long wavelengths. These phenomena were clearly explained by visualizing the wave fronts of surface waves at each time step. Most of the surface wave energy for the reverse testing was confined in the upper soft layer whereas some of energy for the forward testing passes through the lower stiff layer at longer wavelengths.
