Spectral-Analysis-Of-Surface-Waves Testing To Evaluate vs Profiles At Geological Sites

Abstract eng:
The Spectral-Analysis-of-Surface-Waves (SASW) testing method is a nondestructive and nonintrusive seismic method. The method utilizes the dispersive nature of Rayleigh-type surface waves propagating through a layered material to evaluate the shear wave velocity profile. Dispersion in surface wave velocity arises from changing stiffness properties with depth. SASW field testing involves generating surface waves at one location on the exposed material surface and simultaneously measuring the motions perpendicular to the surface created by the passage of surface waves between multiple pairs of surface receivers. All measurement points are arranged along a radial path from the source. Successively larger spacings between receiver pairs and between the source and first receiver are used to measure progressively longer wavelengths. The profiling depth generally equals about one-half of the longest wavelength which also corresponds to the largest spacing between receiver pairs. Spectral analysis is used to separate the waves by frequency or wavelength to determine the experimental (“field”) dispersion curve of the site. A forward modeling or inversion procedure is then used to approximate the field dispersion curve with a one-dimensional system of horizontal layers with varying stiffnesses and thicknesses. The dynamic stiffness matrix method is the modeling algorithm used in the matching or inversion process. SASW measurements are illustrated using four example projects with V S profiles ranging in depths from 5 to 450 m. For the deeper profiling, a large hydraulically-operated mobile shaker, called Liquidator, was used.

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