the spectral-analysis-of-surface-waves (sasw) method is a rapidly developing in situ seismic method for nondestructively determiningyoung's modulus profiles of pavement sites. The method is based on the generation and measurement of surface waves (rayleigh waves). Due to the complex theoretical solution of surface wave propagation inpavements, a multilayered half space with infinite lateral extent has been assumed in the analytical solutions of sasw testing. In addition, only plane surface waves were considered. The existence of direct and reflecte body waves and any reflected surface waves, although known to occur in pavements, was neglected in the analytical solutions. To understand the impact of reflected surface waves and direct and reflected body waves in sasw testing, a simplified analytical model was developed. Reflecting boundaries such as edges or joints of a pavement system or the horizontal interfaces between pavement layers were considered. To examine the validity of the model, field tests on a jointed concrete pavement were performed. The results showthat reflected surface waves cause fluctuations to occur in the field data (dispersion curves) which would otherwise be a smooth function if only direct surface waves were present. Direct and reflected body waves also create a similar result but to a much lesser extent. Reflected sv-waves (shear waves with vertical particle motion) exhibit the most influence of all direct and reflected body waves, with the effect more important at wavelengths longer than the pavement surface layer. The adverse effect of reflections can be minimized by properly orienting the test array (line passing between the source andreceivers) in the field with respect to joints, edges, and cracks in the pavement. For instance, when a vertical reflecting boundary such as a joint is oriented perpendicularly to the sasw array, the adverse effect of reflections can be minimized and nearly eliminated byplacing the source between the reflecting boundary and the receivers. When a vertical reflecting boundary such as the pavement edge is near the zone of testing, the effect of reflections can be greatly minimized by orienting the array parallel to and near (about 0.1 Times the receiver spacing) the edge. This paper appears in transportation research record no. 1196, Pavement evaluation and rehabilitation.
Abstract