Characterisation of heavy traffic axle load spectra for mechanistic-empirical pavement design applications

Heavy traffic axle load spectrum (ALS) is one of the key inputs for mechanistic-empirical analysis and design of pavement structures. Frequently, the entire ALS is aggregated into number of equivalent single axle loads or assumed to have constant contact area (CCA) or constant contact pressure. These characterisations affect the accuracy and computational performance of the pavement analysis. The objective of this study was to evaluate these characterisations based on predicted performances to rutting and fatigue cracking of several pavement structures subjected to ALS data collected from 12 bridge weigh in motion stations. The results indicated that for layers below the top 25cm, all characterisations produced similar values of predicted rutting. However, for the top 25cm, the methods differed in the predicted performances to rutting and fatigue cracking. Furthermore, an improvement to the CCA approach was proposed that enhanced the accuracy while maintaining the same level of computational performance.