Implementation of Reliability-Based Backcalculation Analysis

The reliability concept provides a means of incorporating some degree of certainty into the pavement design process to ensure that the outcomes of the process will provide acceptable levels of service until the end of the intended design life. Pavement structural performance and rehabilitation design are highly dependent on the in situ layer properties. Pavement layer thickness is an essential input in backcalculation analysis performed with measured surface deflections to evaluate the in situ structural capacity of a pavement. Inaccurate thickness information may lead to significant errors in the backcalculated layer moduli and, hence, in the rehabilitation design. Because pavement layer thickness has some degree of variability (normal variability), it is important to consider this variability in the backcalculation analysis and rehabilitation design. A procedure was developed to implement the reliability concept in backcalculation analysis to account for the normal variability in layer thickness within structurally homogeneous sections. This procedure was developed on the basis of in situ layer information obtained from a ground-penetrating radar study performed for the New Jersey Department of Transportation. This paper provides an overview of the procedure, along with the results of the pilot implementation of the procedure. This reliability procedure complements the reliability factor of the 1993 AASHTO pavement design guide, as the latter reliability factor does not account for the in situ layer thickness.