ABSTRACT

The Spectral-Analysis-of-Surface-Waves (SASW) method is a nonintrusive seismic method for evaluation of shear stiffness profiles at geotechnical sites from surface wave measurements. Recent field experience has demonstrated the complexity of interpreting surface wave data at sites with large and abrupt stiffness changes. Geotechnical sites in polar environments as well as offshore sites containing gas hydrates have the potential to exhibit such strong stiffness contrasts which create multiple wave groups and result in complex phase spectra that can be easily misinterpreted. To aid in the correct interpretation of SASW data collected at such complex sites, a new phase interpretation scheme, called, "Impulse Response Filtration" (IRF), is proposed. This filtered impulse response leads to a clearer interpretation of the phase differences between receivers. The IRF method is explained and demonstrated using experimental results from a pavement site which closely simulates frozen over unfrozen geotechnical sites representative of polar environments.

INTRODUCTION

The Spectral-Analysis-of-Surface-Waves (SASW) method has been successfully employed in many geotechnical environments to non-intrusively determine the shear stiffness profile of these sites (Stokoe, et al., 1994). SASW testing involves measurement of the phase difference between vertical surface wave motions at two or more sensor locations. From the phase difference measurements, the phase velocity of the surface wave as a function of wavelength is determined. The phase velocity vs. wavelength relationship is referred to as a dispersion curve, which represents the "field signature" of the site under evaluation. The experimental dispersion curve is then matched with a theoretical dispersion curve in order to determine the shear stiffness profile at the site. Accurate interpretation of the phase velocity data measured in the field is, therefore, a critical step in developing a reliable shear wave velocity profile from the inversion procedure.

This content is only available via PDF.
You can access this article if you purchase or spend a download.