Practical considerations for array-based surface-wave testing methods with respect to near-field effects and shear-wave velocity profiles

Abstract

An important constraint with geophysical testing methods based on the propagation of surface waves (active surface wave testing methods) comes from the filtering criteria that are used to avoid near and far-field effects. Such criteria suggest the use of a large receiver spread length to calculate accurate dispersion curves. However, for geotechnical investigations, the use of such a wide array is at best not desirable due mainly to site constraints and to the nature of the soil profile whose dynamic properties tend to vary laterally. The effectiveness of using smaller arrays of receivers covering limited distances to calculate accurate Rayleigh-waves dispersion curves and shear-wave velocity profiles is investigated. The methods used to compute the phase velocities are based on both group and phase velocity estimates. It is shown that the proposed method reduces the effects of body waves and the possibility of mode misidentification in the near and far-fields even when a limited number of traces covering relatively small distances are used. Also, the properties of the signal processing technique used to calculate the dispersion curves are shown to have a significant impact on the near and far-field effects. Numerical and experimental data are used to show the potential benefits of using shorter arrays of receivers to characterize the properties of different soil profiles with laterally varying properties.