SYMPOSIA PAPER Published: 01 January 1989

Back-Analyzed Elastic Stiffnesses: Comparison Between Different Evaluation Procedures


The PADAL computer program was developed to back-analyze deflection bowls from pavement testing with the falling weight deflectometer. A validation exercise was carried out to check the prediction accuracy of the PADAL computer program in practical applications. The study compared laboratory elastic stiffnesses with the back-analyzed values from PADAL and showed that the best correlation was found for the asphaltic material, with an accuracy of around 20% above measured values. The correlation for granular subbases and clay subgrades was less good. Previous studies comparing in situ stresses and strains confirmed that the nonlinear elastic characterization in the subgrade layer gave significant improvement in the accuracy of prediction compared with a linear representation.

Comparison of dynamic analysis taking account of inertia effects with the static PADAL analysis showed the latter to be quite adequate for use with the falling weight deflectometer.

A simplified back-analysis procedure using the ELMOD computer program was extensively evaluated. It was concluded that this program is best used in predicting stiffnesses of two layered structures consisting of bound asphaltic material overlying the subgrade. In cases of three-layered structures, the prediction of stiffnesses for granular layers was found to be unrealistically large.

Author Information

Tam, WS
SWK Pavement Engineering, Nottingham, Nottinghamshire, U.K.
Brown, SF
University of Nottingham, University Park, Nottingham, Nottinghamshire, U.K.
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Developed by Committee: D04
Pages: 189–200
DOI: 10.1520/STP19807S
ISBN-EB: 978-0-8031-5087-4
ISBN-13: 978-0-8031-1260-5