PSO-Based Multimodal Inversion of Rayleigh-Wave Dispersion Curves for the Geotechnical Characterization of an Embankment Profile

Reliable assessment of small-strain soil stiffness is essential for geotechnical site characterization and for analysing the behaviour of embankments and other earth structures. Surface-wave methods provide an efficient non-destructive means of estimating shear-wave velocity profiles; however, their application is limited by the non-uniqueness of the inversion process. This paper implements and evaluates a PSO-based multimodal inversion framework for Rayleigh-wave dispersion curves in the context of geotechnical characterization of layered soil profiles. The procedure involves the calculation of theoretical dispersion curves for a horizontally layered medium and their matching with experimental data through a global search scheme. The implemented framework was first evaluated using two synthetic soil profiles, and its robustness was further assessed by considering perturbations of the theoretical dispersion curve of up to 10%. Particular attention was given to the influence of higher modes on the inversion results. The results indicate that including higher modes can improve the determination of shear-wave velocity profiles for the analysed cases compared with an inversion based solely on the fundamental mode. The procedure was subsequently validated on a transverse embankment profile using an experimental dispersion curve obtained by multichannel analysis of surface waves (MASW), with comparison against seismic cone penetration test (SCPT) results. Good agreement was obtained, and the eight-layer model proved to be a good compromise between accuracy and model complexity. The results indicate that the implemented PSO-based multimodal inversion framework can support the geotechnical characterization of layered soil profiles for the analysed synthetic and field cases, particularly when modal branches are clearly identified and appropriately included in the inversion.