nondestructive tests are being used more than ever in evaluatingthe integrity of existing pavement systems. The nondestructive tests can be divided into two main categories: (1) deflection-based methods, in which devices such as the falling weight deflectometer (fwd)and dynaflect are used, and (2) wave propagation methods such as the spectral-analysis-of-surface-waves (sasw) method. The sasw method has several significant advantages over deflection-based methods. One advantage is that moduli of thin pavement layers in the upper portion of the pavement system can be easily and accurately measured. A second advantage is that variations in moduli within different layers, especially in the lower portions of the base and in the subgrade, can be evaluated. This feature is particularly beneficial when bedrock is close to surface. A third advantage is that layering in the pavement system does not have to be known. In fact, the thickness of the layers can be determined as illustrated in the modulus profiles presented in the paper. A series of tests was performed at nine flexible pavement sections with significantly different profiles to evaluate the accuracy of layer thickness determination by the sasw method. The thicknesses of the asphaltic-concrete surface layer varied between 1 and 5 in. The base and subbase materials consisted of substantially different materials. No information regarding the types or thicknesses of the layers was provided during data collection or reduction. Only after the results were reported to the texas state highway department were the pavement profiles known. It was found that the sasw method predicted the thicknesses of the layers quite closely.In addition, moduli determined by the sasw method were compared with moduli back-calculated from fwd tests performed at the same sites.The variation in moduli of similar materials used at different sections exhibit somewhat less scatter when obtained from sasw tests. However similar trends were found with both methods. This paper appears in transportation research record no. 1196, Pavement evaluation and rehabilitation.
Abstract