Evaluation of the Federal Aviation Administration methodology for characterizing the nonlinear behavior of granular base and subbase materials

The major pavement test facility for airfields in the United States is the FAA William J. Hughes Technical Center in Atlantic City, New Jersey. This facility is the National Airfield Pavement Test Facility and is housed in a covered hangar on the outskirts of the Atlantic City Airport. Here, a variety of pavement cross sections have been constructed since the late 1990s and trafficked with different load carts, simulating a wide range of aircraft gear types, wheel loads and tire pressures. Arizona State University initiated a study to investigate the possibility of moisture movements in the subgrade clays were occurring due to climatic effects, particularly the thermal gradients. If the hypothesis were validated, it would have the potential to alter the initial design CBR strength parameters used in the performance analysis of the pavement-load sections. This study involved a variety of comprehensive research investigations, covering a wide range of technical topics. One major task of the overall project focused upon an assessment of the nonlinear moduli of the unbound base and subbase layers to investigate the effect of asphalt temperature on the stress state of the pavement profile. This task allowed for the comparison of nonlinear moduli results to the current FAA methodology used in FAA AC-150-5320-6E (FAA, 2009). This publication discusses and presents the moduli results obtained from a comprehensive multi-layer stress analysis of the CC-7 pavement section, for a wide range of load cart configurations, wheel loads and contact areas. While the overall average results of 243 separate pavement computer analysis were found to provide somewhat comparable modulus values, several analytical limitations were found that would lead to relative errors of resilient modulus of base and subbase materials ranging from −60% to +60%. Errors in the modulus of the underlying base and subbase layers are very important as they will lead to significant errors in predicting the subsequent fatigue cracking resistance and predictions of any asphalt surfacing layer.