Non-intrusive Characterization of Shallow Soils and Utility Structures Below Pavements Using Rayleigh Waves

Abstract

When surface waves are used to characterize soils under a pavement, their presence causes problems during the analysis of the signals due mainly to the presence of Lamb waves and higher Rayleigh-wave modes in the signals. Recent studies have shown that these problems can be mitigated if the seismic source is placed on the surface of the soil while leaving the receivers on the pavement. However, the presence of a pavement at the surface of the soil does influence the propagation of Rayleigh waves even if it does not prevent its characterization. We show how we utilized the generalized S transform and the multi-modal analysis of surface waves to identify and separate the different Rayleigh-wave modes. Using 3D numerical models and experimental models, we show that the thickness of the pavement affects the energy distribution of the different Rayleigh-wave modes and that increasing the pavement thickness increases the chances of mode misidentification problems since the energy of the waves tend to travel on higher modes. We also demonstrate that for an underground profile of a given depth, the thickness of the soil layer has more importance than the thickness of the pavement on the Rayleigh-wave propagation energy and velocity. The influence of the pavement on the group and phase velocities of the fundamental Rayleigh-wave propagation mode is also shown to depend on their frequency (wavelength). We present two case studies at the end of the manuscript to confirm the conclusions established based on numerical and experimental models.