Analysis of pavements using an acoustic wave method. II: Inverse process

Measurements of the velocities of surface acoustic waves generated on highway and airfield pavements are capable of providing information concerning the elastic properties of the materials in the pavement layers. The two stages in the use of the acoustic wave method for the evaluation of pavement layered structures are (i) the establishment of the experimental dispersion curve from the data collected in the field, and (ii) the inversion of the dispersion curve to determine the elastic parameters of the system. The establishment of the dispersion curve has been described in detail in a companion paper. Most of the inverse methods developed thus far have been based on numerical procedures, which are greatly time-consuming and depend on the experience of the user. As wave propagation in elastic plates is analogous to propagation in layered structures, a graphical inverse method based on the assumption of the free plate response is presented. This technique provides a fast, useful and economic procedure for determining elastic moduli and thickness of layers in a pavement structure.