Permanent Deformation of an Unbound Granular Pavement Subjected to Accelerated Multiple-Axle Group Loads

Road network owners are being faced with the need to make predictions of the long-term effect of heavy vehicle loading changes on their networks. Exploration of future mass-distance and incremental pricing for heavy vehicles requires an understanding of the effects of different axle group loads and types on pavement performance. The current Australian 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. This ignores the contribution to pavement damage made by the axles in the group which do not correspond with the peak response. The assumption that the deflection response is the most appropriate indicator of pavement damage is also open to question and is not consistent with the current mechanistic design procedures, in which strains rather than deflections are used to calculate the performance of pavement materials. As part of a larger research exercise, the Accelerated Loading Facility was used to apply single, tandem and triaxle (tridem) axle group loads to a typical Australian, full scale, unbound granular pavement and subgrade. Analysis of permanent deformation data was hampered by significant moisture change during the testing period. However it was possible to demonstrate that the current standard load value used for triaxle groups is appropriate. This standard load value assumes that the interaction between axles of a multiple-axle group do not affect the relative permanent deformation damage caused by the same number of ungrouped axles.