The influence of multiple-axle group loads on flexible pavement design

The current Austroads approach to assess the relative damaging effects of different axle groups on road pavements is by comparison of the peak static pavement deflection response under the axle groups. The assumption that deflection is the most appropriate indicator of pavement damage is open to question and is not consistent with the use of strains to calculate the performance of pavement materials. In response, research conducted has determined that, with regard to the fatigue damage of asphalt and cemented materials, the standard load for an axle group type is dependent upon the thickness and modulus of the asphalt and the underlying pavement structure. As a result, it is proposed that the mechanistic design procedure for flexible pavements not use the concept of standard loads, but rather that the procedure determines the pavement damage resulting from each axle load and each axle group within a traffic load distribution. An examination of the implications of pavement design outcomes in using this method determined that in general, reductions in both asphalt and cemented material thicknesses of up to 50 mm would result. The research also determined that the currently used standard loads for tandem, triaxle and quad-axle were appropriate for use with the current empirical procedures for the design of granular pavements with thin bituminous surfacings.