Mechanical response of an unbound granular base course for a flexible pavement

Airfield pavement design is a complex blend of relatively simple linear elastic theory, fatigue concepts, correlations with small and full-scale tests, and pragmatic adjustments to reflect observations of inservice pavements. The granular base and subbase have always posed the most difficult analytical problem in traditional pavement design methodologies. For this reason, the granular layers have never been treated explicitly in design as have the asphalt concrete (AC) layer and subgrade layer, which have used predictive models for cracking in the AC and rutting in the subgrade as a function of linear-elastic strain and material properties. Instead these granular layers were carefully specified in terms of gradation, plasticity, and in-situ density to minimize deformation under traffic However, today's designers are being asked to predict pavement performance under a wide variety of nonstandard conditions. This a far more complex task than simply providing safe thickness and specifications for the material. To deal with this new challenge, the design community must have material models that predict cumulative deformations under repetitive aircraft loads. With heavy loading the nonlinear response of base course materials must be considered when predicting pavement performance. The advances made in computational mechanics have created new tools of application for this type of problem which allow for implementation of theoretically rigorous material models. In order to apply these material models, mechanical response data is required to calibrate the necessary model parameters. In essence, the parameters used to define strength, failure, and deformation properties must be defined for any material to be modeled.