Direct estimation of shear-wave velocity profiles from surface wave investigation of geotechnical sites

Abstract

Surface wave methods have been developed as a commonly used non-invasive tool for shear-wave velocity (Vs) profiling of near-surface soil and rock formations. Inversion is a key step to back-calculate the Vsprofile from dispersion curves; however, the non-linear and ill-posed nature of the problem sometimes yields non-unique Vsprofiles. To overcome these challenges, a new method was developed to circumvent inversion and directly estimate Vsprofiles from the fundamental mode dispersion trend for sites with Vsgradually increasing with depth. This method is developed based on the relationship between the phase velocity of surface waves at a given frequency with the time-averaged shear-wave velocity within a depth of one-half wavelength. Three field sites and three simulated sites covering shallow, medium and deep locations with gradually increasing Vswith depth are employed to verify the feasibility of the proposed methodology. Results indicate that the method can efficiently give a reasonable and realistic estimation of Vsprofiles. The goal of this method is to provide an alternative to obtain Vsprofiles with high certainty and low computational cost for surface wave testing, but not necessarily to find a ‘better’ profile than inversion or to locate each layer interface.