Multi-channel analysis of surface waves (MASW) using dispersion and iterative inversion techniques: implications for cavity detection and geotechnical site investigation

Most of the surface wave-based geophysical methods require an accurate estimate of the shear wave velocity (Vs) for geotechnical site investigation. The Vs gives a measure of shear modulus which is an important engineering parameter and also owns implications for delineating weak zones and cavities. Geotechnical investigation of such zones is imperative to avoid hazards related to high building construction. Among different surface wave-based geophysical methods, the multi-channel analysis of surface waves (MASW) is most widely used technique for geotechnical investigation by measuring in situ Vs. The present work focuses on MASW data acquisition and processing for accurate estimation of Vs by using dispersion analysis and different iteration-based inversion techniques (i.e., Monte Carlo and least square approaches). The proposed methodology is investigated at two sites in Abu Dhabi, UAE, using 24-channel seismograph network. The obtained results suggest that Monte Carlo approach is more efficient and reliable for Vs profile estimation and is recommended for geotechnical investigation. Monte Carlo approach-based results of the MASW velocity-profiles at both sites confirmed cavities and their geometries within the subsurface. Furthermore, the identified cavities are well in agreement with the trail borehole data, thus improving the confidence level of the obtained results. The characterization of the soil of both the sites and its implications are also presented with the help of NEHRP and IBC codes.