A viscoelastic wave propagation approach for dynamic backcalculation of layer properties of asphalt pavements under an impact load

An accurate and efficient asphalt pavement analytical model is crucial in back-calculating reasonable layer properties from falling weight deflectometer data. This study employs the wave propagation approach to address the cylindrical axisymmetric problem for asphalt pavement under an impact load. Different from traditional spectral element method (SEM), continuous integral transforms (Laplace-Hankel transforms) are used to achieve the response solutions for viscoelastic layered media. The modified Havriliak-Negami (MHN) model is incorporated to characterize the viscoelastic properties of asphalt concrete (AC) layer. The MHN model requires only five coefficients to derive various viscoelastic quantities and provides significant advantages in parameter identification. The proposed procedure is validated against response results from finite element method and SEM with a difference of less than 2%, and particularly, it prevents frequency leakage errors that may occur in SEM caused by discrete Fourier transform. A dynamic backcalculation program is then developed by combining the proposed procedure with a screened optimization algorithm. The difference between actual and backcalculated layer parameters of theoretical pavements is found to be less than 3%. Field measured data are also backanalysed, and both dynamic modulus and phase angle master curves are determined to describe the viscoelastic behaviour of AC layer.