This paper aims to investigate complex deformation trends of unbound aggregate layers in airport pavements commonly applied traffic loading with wander. To model realistic effects of offset wheel loads causing aggregate layer movements, as observed in the flexible pavement sections at the Federal Aviation Administration's National Airport Pavement Test Facility, a Discrete Element Modeling (DEM) approach is adopted to enable sliding, rotation, and shifting positions of individual particles in the unbound aggregate layer. The first DEM simulation involving a single rigid plate pushed into an assembly of generated unbound aggregates found that particles moved downward and laterally from under the plate load. The lateral movement caused upward movement of particles adjacent to the plate but not directlyunder it. The DEM simulations of traffic wander involving three plates with each plate sequentially loaded 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. When comparing the single and multiple plate tests, wander resulted in less rutting under the middle plate over a 30-repetition test sequence due to the upheavals causedby offset loads. However, when the number of loads applied on the middleplate only, i.e., traffic coverage, was taken into account, similar rutting was observed due to both traffic wander and channelized loading. In theDEM 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.
Abstract