SYMPOSIA PAPER Published: 01 January 1989

A Mechanistic Method for Evaluation of Layer Moduli and Overlay Design


Nondestructive testing (NDT) has long been used to evaluate flexible pavement structures. The increasing popularity of nondestructive pavement evaluation methods, based on interpretation of surface deflection, has promoted the development of several types of NDT devices. One such device is the falling weight deflectometer (FWD), which is used for the purpose of pavement evaluation in North Carolina. This paper presents a methodology for the testing, evaluation, and determination of overlay thickness required for a given pavement section and subgrade condition. The overlay design procedure presented makes use of some of the recent developments for analysis and design of asphaltic concrete overlays. The evaluation of in-service pavements includes the use of the deflection parameters developed by testing of the existing pavements with known geometry for determining the moduli of various pavement layers and the required overlay thickness. The method utilizes empirical values and the VESYS structural subsystem as an integral approach complementary to each other.

Six pavement sections across the state of North Carolina were selected for deflection testing. Deflection parameters were developed to characterize the deflection data from these pavement sections. In addition, the VESYS structural system was used to develop nomographs for the interpretation of the measured deflection basin parameters. These nomographs were used to backcalculate layer moduli from deflection parameters and known layer thicknesses using iterative solutions. The backcalculated layer moduli from these nomographs correspond to the climate conditions that happen to exist during the time of testing and must therefore be adjusted to other climatic conditions. A procedure for such an adjustment is also included in the design procedure.

Author Information

Khosla, NP
North Carolina State University, Raleigh, NC
Ali, NA
North Carolina State University, Raleigh, NC
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Developed by Committee: D04
Pages: 355–367
DOI: 10.1520/STP19817S
ISBN-EB: 978-0-8031-5087-4
ISBN-13: 978-0-8031-1260-5