PROBABILISTIC DESIGN CONCEPTS APPLIED TO FLEXIBLE PAVEMENT SYSTEMS DESIGN

Abstract

A MAJOR PROBLEM IN PAVEMENT DESIGN HAS BEEN THE INHERENT UNCERTAINTY AND VARIATION OF THE DESIGN PARAMETERS AND MODELS. EMPIRICAL SAFETY FACTORS AND JUDGEMENT FACTORS HAVE BEEN APPLIED TO ADJUST FOR THE UNCERTAINTIES INVOLVED, BUT THE RESULT HAS BEEN MUCH OVERDESIGN AND UNDERDESIGN. A METHOD WAS NEEDED WHICH WOULD CONSIDER THE VARIATIONS AND UNCERTAINTIES OF PAVEMENT DESIGN QUANTITATIVELY AND MAKE IT POSSIBLE TO DESIGN FOR A SPECIFIC LEVEL OF RELIABILITY. AS A BASIC START IN THE SOLUTION OF THE PROBLEM, A THEORY AND PROCEDURES WERE DEVELOPED, BASED ON CLASSICAL RELIABILITY THEORY, TO APPLY PROBABILISTIC DESIGN CONCEPTS TO FLEXIBLE PAVEMENT SYSTEM DESIGN. THE PROBABILISTIC THEORY AND PROCEDURES HAVE BEEN BOTH PRACTICAL AND USEFUL AS THEY HAVE BEEN IMPLEMENTED INTO THE PAVEMENT DESIGN OPERATIONS OF THE TEXAS HIGHWAY DEPARTMENT. ORIGINAL IMPLEMENTATION WAS WITH THE DETERMINISTIC FPS-7 PROGRAM, WHICH WAS MODIFIED TO INCLUDE SOME PROBABILISTIC DESIGN CAPABILITY AND RENAMED FPS-11. THAT VERSION, WHICH HAS BEEN USED BY TEN DISTRICTS OF THE TEXAS HIGHWAY DEPARTMENT SINCE LATE 1971, HAS BEEN FURTHER DEVELOPED TO INCLUDE VARIATIONS OCCURRING IN INDIVIDUAL PAVEMENT LAYERS AND SUBGRADE, AND THE CONSIDERATION OF TRAFFIC FORECASTING ERROR. THE OVERLAY MODE WAS IMPROVED BY MAKING IT POSSIBLE TO ADJUST THE PERFORMANCE MODEL TO A SPECIFIC PAVEMENT BY CONSIDERING ITS PAST PERFORMANCE HISTORY, AND THE NEW PROGRAM WAS NAMED FPS-13 (CFHR).