Influence of multiple-axle group loads on mechanistic design of asphalt pavements

The current Australasian asphalt pavement design process represents the spectrum of design traffic n axle group types and load levels n as a single number of repetitions of a standard axle load. The translation of a spectrum of load types/levels to a single number is based on assumed load levels that cause the same deflection as the standard load. Further, it is assumed that this conversion is constant across all pavement configurations. Based on French laboratory research, which simulated axle groups as a sequence of equal peak strains representing individual axles in a group, a more realistic model of asphalt damage can be achieved. This is done using the existing Austroads asphalt fatigue model and individual axle peak strains for load increments in each axle group. This design approach, which is validated against the French research outcomes, requires the separate modelling of each combination of axle group type and load level, similar to that conducted for rigid pavement design. By moving away from the intermediate step of conversion of the design traffic spectra to standard loads, the proposed approach would harmonise traffic characterisation for flexible and rigid pavements. A reduced asphalt thickness of up to 50 mm is also demonstrated to occur for moderately and heavily trafficked pavements.