In addition, it is planned that four drop heights will be used to apply four different load levels at a single location. 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. 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. Current studies are aimed at identifying specific problems leading to unacceptable variations in backcalculated moduli when using different computer codes and closure tolerances. These moduli must be calculated using standard procedures representing the state of the art. Also, these in-situ responses were being used to estimate the residual life of in-service pavement and also defining various maintenance strategies such as overlays etc. The backcalculated layer moduli are critical to the development of calibrated mechanistic-empirical models for a variety of uses. These in-situ responses were being analyzed by a predominant technique known as backcalculation to estimate resilient layer moduli (ASTM, 2007, Senseney et al., 2010). 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.
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).
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