USE OF SURFACE WAVES IN PAVEMENT EVALUATION.

Material characterization of pavement systems in situ is required for determining load capacity and assessing the performance and possible need for rehabilitation or replacement of the system. Nondestructive tests are usually carried out for this purpose. Desirable features of nondestructive tests are speed of operation, economy, and a sound theoretical basis compatible with the in situ data collection procedure. The most popular methods in this category are the falling weight deflectometer (FWD) and the Dynaflect. These methods are fast for in situ data collection; however, a rigorous data-reduction algorithm that can result in a unique solution and take into account the effect of the dynamic nature of the load has only begun to be developed. An alternative method of nondestructive testing has been under continuous development at the University of Texas. This method is called the spectral-analysis-of-surface-waves (SASW) method and is based on the theory of stress waves propagating in elastic media. The SASW method can be utilized to determine Young's modulus profiles of the pavement structure and underlying soil as well as the thickness of each layer. In this paper the theoretical aspects of the SASW method are discussed in detail. The experimental procedure is included only briefly because it has been presented comprehensively in earlier papers. Several case studies on different types of pavements with various thicknesses are presented to demonstrate the utility and versatility of the SASW method. In each case, the results are compared with those of the well-established crosshole seismic test that was performed at the same locations. The Young's modulus profiles from these two independent methods compare closely.