VERIFICATION OF BACKCALCULATION OF PAVEMENT MODULI

This paper introduces a backcalculation computer program which can be used to estimate the elastic modulus for each pavement layer. This microcomputer program, EVERCALC, is based on the Chevron N-layer elastic analysis computer program and was developed primarily for flexible pavement analysis and falling weight defectometer (FWD) data. The program is capable of estimating the elastic modulus for each layer of a pavement structure (up to a maximum of three layers) directly from surface deflection measurements. Further, the stress sensitivity coefficients for unstabilized layers (both base and subgrade) are estimated, as well as a standard asphalt concrete modulus analogous to a laboratory condition. Results from EVERCALC were verified in two ways. The first approach was to compare theoretical and backcalculated moduli for a range of three layer pavements. These comparisons showed modest differences among the moduli (about 8% for asphalt concrete, 6% for base course, and less than 2% for the subgrade soils). The second verification approach was to compare backcalculated and laboratory moduli based on FWD tests and field material sampling, along with appropriate laboratory testing. In general, the differences in moduli are significantly less than the natural variation of these materials within a relatively short pavement segment. (Pavement segments were originally selected for their apparent uniformity.)