COMPARISON OF PAVEMENT DEFLECTION ANALYSIS METHODS USING OVERLAY DESIGN

Four pavement deflection analysis methods, in the form of personal computer software programs, were evaluated and compared from the practitioner's perspective on the basis of calculated overlay design thickness, common characteristics, and performance. These programs are ELSDEF, MODCOMP2, MODULUS4, and ISSEM4. Each program applies the concept of backcalculation, which is the determination of in situ material properties of a pavement structure from its response to dynamic surface loading. A total of 29 in-service, flexible pavement sections, requiring significant rehabilitation, were selected from areas of various environmental conditions, traffic loading, and subgrade soil types in Arizona. Through backcalculation, actual falling weight deflectometer field deflections were used to estimate layer moduli of all pavement sections. The moduli results were then used in the overlay design of each section in accordance with the 1986 AASHTO Guide for Design of Pavement Structures. Although the four backcalculation programs are characteristically different, neither layer modulus nor overlay thickness results were statistically different in most cases. However, from a practical perspective, backcalculation, as represented by these programs, is not adequate for use by the practitioner. Additional research is needed to refine the backcalculation process.