Difficulties with phase spectrum unwrapping in spectral analysis of surface waves nondestructive testing of pavements

Abstract

Spectral analysis of surface waves (SASW) is a nondestructive and in situ method for determining the stiffness profiles of soil and pavement sites. This method involves the generation and measurement of surface Rayleigh waves. By exploiting the dispersive characteristic of these waves in layered systems, the SASW method provides information on the variation of stiffness with depth. This paper presents the results of a case study for near-surface profiling of a pavement site using the SASW method. In this study, inconsistencies were observed in the dispersion curve of the site when the usual procedure of unfolding the relative phase spectrum was followed. A correction procedure to eliminate these inconsistencies is suggested and discussed. The thickness and wave velocities of the various layers obtained with the SASW method, after applying the correction procedure, matched closely those determined from cored samples and cross-hole tests. Key words : nondestructive testing, pavement, layered media, Rayleigh wave, spectral analysis, shear wave velocity, wave propagation.