Design Index and Model for Controlling the Permanent Deformation of the Granular Base Course

This study proposes a design index and model for controlling the permanent deformation of the granular base course for asphalt pavements by adopting two types of graded macadam. Three levels of confining pressure stresses and different stress ratios were set as the test loading conditions. The permanent deformation shakedown characteristics of the graded macadam were examined by conducting triaxial repeated load testing based on shakedown theory. Statistical regression and curve fitting were applied to the test results to overcome the limitation on the number of repeated loads. In accordance with the fitting results, the testing curves were extended to analyze the limit stresses for the shakedown under different shakedown statuses of the permanent deformation of the aggregates. A new design model was established for controlling the permanent deformation of the granular base course in zone A (plastic shakedown status). The permanent deformation of granular base courses of typical asphalt pavement structures was calculated by adopting the layer-wise strain summation and employing the evaluation model currently adopted by the United States’ Mechanistic-Empirical Pavement Design Guide for the permanent deformation of granular base courses. Consequently, the critical standard values of the permanent deformation and the permanent strain of granular base courses were determined. The stress ratio is recommended as a design index for controlling the permanent deformation of the granular base course. The control model of the regression formula between the stress ratio and the number of axial loading was originally created based on laboratory tests.