Permanent Deformation Behavior of the Granular Layers Tested at the FAA’s National Airport Pavement Test Facility

The National Airport Pavement Test Facility (NAPTF) is located at the FAA William J. Hughes Technical Center, Atlantic City International Airport, New Jersey. It is used to generate full-scale pavement response and performance data for development and verification of airport pavement design criteria. Additional information is available on the FAA Airport Pavement Technology web site, www.airporttech.tc.faa.gov. During the first series of traffic tests, 6 flexible pavement test items were subjected to accelerated traffic tests using representative full-scale aircraft landing gear configurations. The test items were trafficked with 4- and 6-wheel gear loads with permanent deformations at the surface evidenced by rut depths of over 4 inches and in some cases upheaval at the sides of the ruts in excess of 1 inch (25.4 mm). Vertical deformations were measured with multidepth deflectometers (MDDs). This paper presents the permanent deformation accumulation at the surface, in the base, the subbase, and subgrade layers. The permanent deformations increased significantly as the pavement was trafficked. Characteristics of the change in permanent deformation measured by the MDDs were: 1) an initial shakedown period where the permanent deformation increases rapidly; 2) an extended period of consolidation where the deformation appears to be approaching an asymptotic limit; 3) a period of increasing rate of deformation probably associated with the initiation of shear failure; and 4) a period of bulk transverse movement of the material in the layer, or layers, undergoing shear flow. The 4th stage needs to be confirmed in future traffic tests.