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Falling weight deflectometer (FWD) testing is a nondestructive pavement structural evaluation technique routinely performed on highway and airfield pavements to estimate pavement layer properties from measured deflection basins. This paper presents a methodology based on analyzing FWD test data between trafficked and nontrafficked lanes to determine the degradation and rutting potential of flexible pavement unbound aggregate layers in comparison to the subgrade damage. The validity of the approach is demonstrated by analyzing the heavy weight deflectometer (HWD) data obtained from the FAA's National Airport Pavement Test Facility (NAPTF) flexible airport pavement test sections built with substantially thick unbound aggregate base–subbase courses. The modified base damage index and base curvature index defined from HWD pavement deflection basins were used to determine relative base-to-subgrade damage, which clearly showed evidence of the increased base damage induced in the NAPTF airport pavement layers during trafficking partly due to the applied aircraft gear load wander. This was in accordance with both the individual pavement layer recovered and unrecovered (inelastic or residual) deformation trends identified from analyzing the multidepth deflectometer data collected during trafficking and the post-traffic forensic analysis results, which indicated that a majority of the permanent deformation occurred in the unbound aggregate layers and not in the subgrade. The methodology presented for the detailed analyses of the FWD (or HWD) test data between trafficked and nontrafficked lanes can be effectively used in flexible pavements to detect unbound aggregate layer deterioration and the pavement damage potential due to that deterioration.

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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.