TRR No. 1260 Pavement Design, Management And Performance, pp. 42-52
The Spectral analysis of surface waves (SASW) method is a nondestructive testing procedure under development for determining the elastic modulus profile of pavement systems in situ. The ultimate objective for practical use of the SASW method is the design of a totally automated, movable test rig for investigating pavement systems. An important step toward this objective would be the development of a multiple-transducer testing procedure in which the source-to-near-receiver distance S and source type are significant variables. Tests conducted on two asphaltic concrete pavements to study the effects of these varables determined that the ratio of S to receiver spacing X should be 2. In addition, dispersion data were independent of S when wavelengths longer than 2x were eliminated from the data. The effect of source type on the ranges of useful frequencies for a given value of X was significant. In general, both the lower and upper cutoff frequencies decreased as the weight of the source increased. The dispersion curves generated with the data were compared with optimum ones using a constant source type. Although no single source type consistently yielded an optimum dispersion curve, combining the data from a 4-oz ball peen hammer and an 8-lb sledge hammer yielded an optimum dispersion curve over all wavelengths.