Effect of heavy multi-axle trucks on flexible pavement rutting

In this study, heavy axle and truck configurations were investigated to determine their influence on flexible pavement rutting. Several approaches were considered: (1) analysis of State of Michigan, in-service pavement data to investigate the effect of multi-axle trucks on total pavement rutting damage; (2) laboratory simulation of multiple axle and truck configurations to study their effects on asphalt concrete rutting; and (3) mechanistic analysis of rutting damage due to multiple axle and truck configurations using a newly calibrated mechanistic-empirical rutting model.; The analysis of in-service pavement data showed that damage caused by multiple-axle truck configurations is more significant, showing higher beta values than single- and tandem-axle truck configurations. This indicates that rutting is most influenced by axle/truck gross weight. In calibrating the VESYS rutting model, time-series, in-service pavement data were used from the SPS-1 experiment. This important methodological improvement over previous studies permits more accurate determination of the permanent deformation parameters (PDP) that lead to better agreement with results from accelerated loading facilities. Analyses of layer rutting contribution of in-service pavement data showed that, on average, the total amount of rutting breaks down as follows: 57% HMA rutting, 27% base rutting, and 16% subgrade rutting. These results suggest that accounting for subgrade rutting only is no longer valid for designing flexible pavements.; The laboratory investigation indicates that the rutting damage due to different axle configurations is approximately proportional to the number of axles. Calculating truck rutting damage by simply summing the vertical permanent deformation corresponding to its constituent axle groups result in erroneous predictions. Using Miner's rule to determine truck rutting damage from its constituent axles does improve the prediction, although there are still variations among the damage values corresponding to different axle and truck configurations.; The results from mechanistic analyses showed that there is little to no interaction between axles in the vertical strain within the HMA layer. For the vertical strain within the base layer, the interaction between axles increases with increasing HMA layer thickness. On the other hand, there is always high interaction between axles in the subgrade layer (vertical strains). Despite the interaction between axles, the mechanistic analysis in this study confirmed the laboratory findings related to the proportionality of axle and truck factors for the HMA layer. Moreover, it extended this same result to include both the base and subgrade layers.