Numerical Investigation of Impedance Variation Effect on Surface-Waves’ Propagation for Characterization of Very Soft Soils

ABSTRACT: The characterization of soils by using near-surface geophysical techniques has been gaining attention in the geotechnical engineering practice in the last two decades. The multi-channel analysis of surface waves (MASW) is a geophysical technique for profiling shear wave velocity in a soil by applying inversion techniques from the dispersion curve. Numerical simulations were performed to understand the limitations of MASW technique when characterizing very-soft soils. Results show that shear wave velocities and layer thicknesses of very-soft materials can be estimated with uncertainty about 2%. However, the acoustic impedance ratio between adjacent soil layers has effect in the MASW results interpretation. From the results it is possible to conclude that the lower the impedance ratio the higher the diffusion of seismic energy. Based on these results it is possible to define a threshold value for the impedance ratio beyond which the use of MASW technique becomes unfeasible to characterize very-soft soils.