Effect of aircraft load wander on unbound aggregate pavement layer stiffness and deformation behavior

Load wander in airport pavements is much wider than highway wander due to the varying paths of different aircraft gear configurations and applied wheel loading locations. Full scale pavement testing of aircraft loads at the FAA's National Airport Pavement Test Facility (NAPTF) indicates that wander can negate the stiffening in unbound granular layers, known as the shakedown effect, and make them prone to developing increased deformations on subsequent aircraft passes when compared to channelized highway traffic. As part of the research activities at the FAA's Center of Excellence for Airport Technology (CEAT) established at the University of Illinois, dynamic response data from airport pavement test sections were collected due to passing of each of the 6-wheel B777 type and the 4-wheel B747 type gears for various combinations of applied load magnitudes and loading sequences (application order and stress history effects), traffic directions, gear spacings, and wander positions and sequences. The field data analyzed showed that the permanent deformation during a complete wander cycle was negated due to aircraft wander, indicating recurring particle movements and rearrangements in the unbound pavement layers. Using the multi-depth deflectometer data and the concepts of base damage index and base curvature index from heavy weight deflectometer testing, the load wander was determined to cause high percentages of residual responses per wheel pass in the granular layers that were indicative of reduced strength and modulus properties for potentially higher damage accumulations during the initial stages of NAPTF test section trafficking to failure.