Multifrequency back-calculation of pavement-layer moduli

This paper introduces a frequency-domain back-calculation program, BKGREEN, that can be used to determine the elastic modulus for each pavement layer. The pavement is modeled as a layered elastic system resting over a rigid bedrock or a half-space in terms of dynamic Green flexibility influence functions. A nonlinear least-squares technique is implemented for matching the measured and calculated deflection response functions. The theoretical results show that (1) the use of multifrequency back-calculation can lead to satisfactory convergence of layer moduli even when the number of receivers is less than the number of layers to be determined; therefore, it overcomes the limitation on the maximum allowable number of layers in most static back-calculation programs; and (2) the program has the potential to cope with difficult situations, such as the existence of extraordinarily thin layers, or shallow hard layers, as well as the degradation of surface layers due to cracking, or temperature and moisture gradients. After studying real field deflections at five test sites, we find that the moduli back-calculated using quasi-static frequency in the BKGREEN program compare well with the other five developed programs.