The backcalculation process is usually iterative and normally done with computer software. The combination of assumed layer stiffnesses that results in this match is then assumed to be near the actual in situ moduli for the various pavement layers.
The assumed layer moduli in the calculated model are adjusted until they produce a surface deflection that closely matches the measured one. Backcalculation takes a measured surface deflection and attempts to match it (to within some tolerable error) with a calculated surface deflection generated from an identical pavement structure using assumed layer stiffnesses (moduli). Therefore, it is important to consider the dynamic effects in interpreting FWD data.“ Backcalculation” is a mechanistic evaluation of pavement surface deflection basins generated by various pavement deflection devices. The dynamic and quasi-static viscoelastic responses are compared and the results show that the inertia and damping behaviour greatly influences the surface deflection of asphalt pavement under FWD loading, especially for pavements with cemented treated base. A computer code is developed to implement the SEM procedure and the results are in good agreement with finite element analysis. The MHN model can accurately characterise the viscoelastic and damping behaviour of AC with much fewer number of model coefficients (only five) than the widely used Prony series representation, which makes the model well suited for the dynamic response analysis and backcalculation of layer properties. The modified Havriliak–Negami (MHN) mode is used to characterise the mechanical properties of asphalt concrete (AC). This study uses the spectral element method (SEM) to analyse the dynamic viscoelastic response of asphalt pavement subjected to FWD loading.
The response analysis mode of asphalt pavement plays a critical role in properly interpreting falling weight deflectometer (FWD) test results and obtaining reasonable backcalculated layer properties.
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