Nondestructive deflection testing using falling weight deflectometers is one element of the monitoring effort planned by the Strategic Highway Research Program (SHRP) for the Long-Term Pavement Performance Studies (LTPP). Nondestructive deflection testing provides data for the backcalculation of moduli for the various pavement structural layers, as well as critically important data on material variability that is expected to be an important independent variable in future pavement performance prediction models. The backcalculated layer moduli are critical to the development of calibrated mechanistic-empirical models for a variety of uses. These moduli must be calculated using standard procedures representing the state of the art. Current studies are aimed at identifying specific problems leading to unacceptable variations in backcalculated moduli when using different computer codes and closure tolerances. It is expected that these studies will provide a wealth of information which will be useful as SHRP planning for the use of deflection testing proceeds. Backcalculated moduli from measurements at a number of locations within a test section are to be used to establish the mean, minimum, maximum, and standard deviation of moduli for each layer. In addition, it is planned that four drop heights will be used to apply four different load levels at a single location. Four load levels should provide the variations in layer moduli with stress sensitivity.
Presently it is planned to use nondestructive testing to study variations in deflections and moduli on a seasonal basis, especially variations through the spring thaw in northern climates. These studies should provide critically important information that has been a severe limiting factor in past attempts to predict the performance of pavements subjected to spring thaw conditions. While major damage occurs to pavements during the spring thaw, these conditions have never been adequately accounted for on a mechanistic basis.
This paper summarizes current (as of Spring 1988) SHRP planning for the utilization of nondestructive deflection testing in their Long-Term Pavement Performance Studies. The plans presented herein are preliminary. It is hoped that this presentation will generate comments as well as constructive criticism, which might be incorporated into SHRP plans before work has progressed to a point where changes are difficult to make.