DETERMINATION OF LAYER MODULI FROM FWD MEASUREMENTS

In this study, a comparison of two backcalculation programs with different calculation methods, Modulus and Elmod, is made using Falling Weight Deflectometer (FWD) data derived from 43 SHRP-LTPP (Strategic Highway Research Program, Long-Term Pavement Performance) test sections in Finland. Higher subgrade modulus values are obtained with the Elmod-program than with the Modulus-program. Consequently, the Modulus-program yields higher values for asphalt layer modulus than the Elmod-program. Variation in the backcalculated layer moduli is somewhat greater within the Modulus-program than the Elmod-program. The base course modulus was found to be the most stress-sensitive of pavement layers, since the stress level is also highest in the base course of unbound pavement layers. Critical strains were calculated using the linear program (BISAR) with layer moduli from the Modulus-program as input and with the Elmod-program. It was found, that the calculated strains from the two programs agree very well, even though the calculated moduli are quite different. (A) For the covering abstract see IRRD 883133.