Flexible Pavement Design System FPS 19W: User's Manual (Reprint)

FPS 19W is the approved flexible pavement thickness design system used by the Texas Department of Transportation (TxDOT). Project 0-1869 made several enhancements to this system, including: . transferring the system to the Windows@ platform, . automating the Texas Triaxial system to provide a thickness checking system, . incorporating stress and strain computational subsystem so that classical fatigue and rutting lives can be estimated for the designed pavement, and . incorporating an extensive on-line help system. In this project the models within FPS 19W were further calibrated. New approaches were also incorporated for handling designs on pavements with very thick flexible bases. A comparison between the new FPS 19W and the existing FPS 11 program is presented in the Appendix of this report. For pavements with flexible bases, the two programs will give similar designs if the reliability levels are adjusted (Level D in FPS 11 appears equivalent to Level C in FPS 19W). Care must also be taken in assigning base moduli on pavements with weak subgrades; using fixed values can lead to under-designs. For thicker pavements, FPS 19W does not give as much significance to subbase and subgrade support. Consequently, the design in FPS 19W will be more conservative than those designs generated by FPS 11.