ANALYTICAL EVALUATION OF VARIABLES AFFECTING SURFACE WAVE TESTING OF PAVEMENTS.

Abstract

Spectral-Analysis-of-Surface-Waves (SASW) is a promising nondestructive technique for evaluating the mechanical properties of pavement systems and soil deposits. In applying the technique, it is assumed that only plane Rayleigh waves are generated by the source. In reality, when an impulse is applied at the top of a layered system, body waves (shear and compression waves) and other types of surface waves are produced along with Rayleigh waves. In this paper, the dispersion curves (frequency or wavelength versus phase velocity) obtained by assuming only plane Rayleigh waves are compared with dispersion curves obtained when all types of waves are considered. Several cases with different types of layering are studied, and emphasis is placed on typical pavement systems. It is found that the receiver arrangement can significantly influence the dispersion curve and, hence, the resulting modulus profile. For a typical SASW setup in which the distance from the source to the first receiver is kept equal to the distance between the two receivers, wavelengths considered during analysis of the field data should be equal to or less than one-half of the distance between receivers. If this filtering of low frequencies is not performed, the assumption that only plane Rayleigh waves propagate through the medium can lead to errors when backcalculating physical properties from the dispersion curve.