Since the early 1900s, many empirical methods have been developed for the structural design of pavements. The empirical nature of these methods was necessary because of a limited knowledge of materialbehavior as well as limitations in the ability to solve boundary value problems. Empirical methods may be adequate for a range of established conditions; however, it is difficult to extrapolate such methods beyond the conditons for which they were developed. The desirability of extending the range of pavement design methods to include new materials, widely varying environmental conditions, and changing loading conditions requires a more fundamental and analytical approach to the design of pavement structural systems. The method should probably be based on a rational (theoretical) basis, with the capability to predict the performance of a pavement over its useful (i.E., Design) life. One of the latest rational methods proposed is the vesys iiia computer-based approach developed through fhwa. The vesys iiia computer program was used to predict pavement performance in termsof rutting, fatigue cracking, and a present serviceability index (psi) for the louisiana experimental base project. It was found that the vesys iiia mechanistic analysis package, in combination with material characterization information developed from resilient indirect tensile tests, can adequately predict rut depths over a short periodof time but inadequately predicts fatigue cracking. Comparisons between measured and predicted psi values indicated that the vesys iiiamodel may be adequate for short periods of evaluation. This paper appears in transportation research record no. 1307, Pavement analysis, design, rehabilitation, and environmental factors 1991.
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