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At the present time, numerous computer programs are available for backcalculating layer elastic moduli using deflection basins obtained by nondestructive testing. These programs usually utilize both a forward calculation and a backcalculation scheme. This paper presents the results of a study made of several of these computer codes with deflection basins obtained from several low-volume (surface-treated) road sections using a falling weight deflectometer (FWD). A nonlinear finite-element program (ILLIPAVE) was first used to backcalculate the layer moduli of the surface-treated pavement sections using FWD deflection basins by the trial-and-error approach. A pavement dynamic cone penetrometer (PDCP) was also used (in situ) to measure the layer moduli. Several backcalculation programs, namely, BISDEF, CHEVDEF, ELSDEF, ISSEM4, MODCOMP2, LOADRATE, and MODULUS then were used to backcalculate the layer moduli. The forward calculation schemes considered include: BISAR, CHEVRON, ELSYM5, NELAPAV, and ELMOD was well as ILLIPAVE. All of these programs, including ILLIPAVE, are microcomputer based. The paper also includes an example problem which involves backcalculating the layer moduli of a 30.48-m (100-ft) stretch of a typical farm-to-market road in which deflection basins were taken at one-foot spacings.
low-volume road, backcalculation, pavement, dynamic cone penetrometer, layer moduli, elastic moduli, falling weight
Assistant professor, University of New Mexico, Albuquerque, NM