Unbound Aggregate Deformation Behavior due to Traffic Wander

This paper reports the investigation of complex deformation trends observed in unbound aggregate layers of airport pavements and caused by traffic loading with wander, as seen in the flexible pavement sections at FAA's National Airport Pavement Test Facility. A discrete element modeling (DEM) approach was adopted to enable realistic movements (i.e., sliding, rotating, and shifting positions of individual particles in the unbound aggregate layer in response to offset wheel loads). The first DEM simulation involving a single rigid plate pushed into an assembly of generated unbound particles found that the particles moved downward and laterally from under the plate load. The lateral movement caused upward movement of particles adjacent to the plate. The DEM simulations of traffic wander involving three plates, with each plate loaded sequentially, found that the particles were forced back under the previously loaded plate due to the application of the next offset load, which caused upheaval of the first plate. Comparison of the single- and multiple-plate tests showed that wander resulted in less rutting under the middle plate over a 30-repetition test sequence due to the upheavals caused by offset loads. However, when the number of loads applied on the middle plate only (i.e., traffic coverage) was taken into account, similar rutting was observed due to both traffic wander and channelized loading. In the DEM simulations, wander caused substantially more particle rearrangement and movement, which could result in greater deformation upon further loading due to higher rutting rates and associated material degradation.