Pavement moduli variation under heavy aircraft trafficking

Heavyweight deflectometer (HWD) tests at 160·2 kN (36 000 lb) force amplitude were periodically conducted at the US Federal Aviation Administration's National Airport Pavement Test Facility (NAPTF) to monitor the effect of Boeing 777 and Boeing 747 test gear trafficking on the structural condition of pavements. In this study, the changes in back-calculated pavement moduli with trafficking were used to compare the relative severity of the aircraft landing gear on the test sections. ILLI-PAVE, an advanced finite-element flexible pavement structural model that can accommodate non-linear unbound material properties was used to model the NAPTF test sections under the HWD loading and synthetic databases were generated. Regression algorithms relating the moduli to HWD deflection basin parameters were developed for predicting asphalt concrete and sub-grade moduli from NAPTF HWD test data. The traffic lane back-calculated moduli values were compared with the untrafficked centreline moduli values to study the loss of stiffness as a result of trafficking. The results were finally compared with those obtained using conventional elastic layer program-based back-calculation software. The results indicate that both test gears have similar potential in terms of their damaging effect on airport flexible pavements.