Effect of Granular Subbase Thickness on Airfield Pavement Structural Response

The effects of variable granular subbase thickness on the structural responses of flexible airport pavement test sections subjected to six-wheel and four-wheel multiple-wheel heavy aircraft gear loading are discussed. Four low-strength subgrade flexible pavement sections at the National Airport Pavement Test Facility (NAPTF) with different subbase thicknesses (406, 610, 864, and 1,092mm) were considered. Heavy weight deflectometer (HWD) tests were conducted prior to traffic testing to document the uniformity of the test pavements. Surface deflection basins were obtained and the layer moduli were back-calculated. Traffic tests were conducted on test sections with the intention of failing the subgrade; in the meanwhile, rutting was monitored periodically. A two-dimensional pavement finite-element program was used to model the NAPTF test sections and compute the critical structural responses. Test sections with lower subbase thicknesses showed higher HWD maximum surface deflections (D0) and higher computed subgrade deviator stress. However, an increase in the subbase thickness did not reduce the deviator stress in the pavement. Test sections with lower subbase thicknesses showed higher levels of early life rut depth development. The development of surface rut depths with increasing number of load repetitions was characterized using the Power model and regression models were developed to predict rutting model parameters as functions of measured and computed initial structural responses.