Impact of Roughness-Induced Dynamic Load on Flexible Pavement Performance

Abstract

This study deals with the impact of roughness-induced dynamic load on flexible pavement distress and performance. It involves field measurements of dynamic axle loads using the instrumented vehicle developed by the National Research Council in the context of the Road and Transportation Association of Canada Weights and Dimensions Study. Pavement distress and performance are modeled using a modified version of the Federal Highway Administration's (FHWA) VESYS-III-A model. Measured standard deviations of dynamic load ranged from 8 to 42 kN, depending on vehicle speed, pavement roughness, and suspension type where the corresponding static load values were approximately 205 kN. It was concluded that for vehicle speeds higher than 40 km/h, the rubber suspension yields dynamic loads substantially higher than the air suspension. Furthermore, dynamic load waveforms from replicate runs were found repetitive in space. Although this loading condition is clearly not the case for pavements under in-service traffic, it was typical of the loading experienced by American Association of State Highway Officials (AASHO) Road Test sections. As a result, the latter is considered poorly randomized with respect to the impact of dynamic load. A method is described for modeling the impact of the repetitive in space dynamic load experienced by a number of AASHO Road Test sections. Ten sections were analyzed, six of which developed severe roughness through their service lives. The methodology improved considerably the accuracy of performance predictions for four out of the six rough sections analyzed. Another part of the study examined the impact of suspension type on pavement performance assuming random application of dynamic loads. Performance predictions for the two suspensions were compared on the basis of the relative areas under the performance curves. With respect to the static load, the rubber suspension caused 17 and 22% additional damage for terminal serviceability values of 2.0 and 2.5, respectively. The corresponding values for the air suspension were 6 and 8%, respectively.