SENSITIVITY ANALYSIS OF SELECTED BACKCALCULATION PROCEDURES

Abstract

One major problem facing highway engineers today is the evaluation of existing pavement systems. This evaluation is necessary to meet today's demands for higher magnitudes of traffic loads and intensity. In particular, there exists a need for a reliable, quick, and nondestructive tool that permits the evaluation of pavements to obtain accurate information about existing structural conditions. In response to this need, several types of nondestructive testing equipment and analysis procedures have been developed and are currently available. Their use in predicting pavement layer moduli must be carefully evaluated, as this particular application is now an integral part of the new AASHTO overlay design procedure. BISDEF, MODCOMP2, and SEARCH analysis procedures were evaluated and the sensitivity of the backcalculated moduli to variations in input parameters was investigated. Results obtained for typical asphalt concrete and aggregate-surfaced pavements showed that the backcalculated moduli were sensitive to several of the user-supplied inputs. The backcalculated moduli from BISDEF were sensitive to layer thickness, depth of stiff layer, and assumed range of layer modulus used. For the MODCOMP2 and SEARCH programs, the backcalculated moduli were sensitive to layer thickness. Backcalculated moduli from all three programs were sensitive to variations in surface deflection measurements. Although identical values were input, the backcalculated moduli from the three procedures differed.