Analysis of Repeated Network-Level Testing by the Falling Weight Deflectometer on I-81 in the Virginia Department of Transportation's Bristol District

This study was undertaken in an effort to determine the required time between subsequent rounds of network-level pavement deflection testing using a falling weight deflectometer (FWD) on the Virginia Department of Transportation’s (VDOT’s) interstate system. Network-level deflection testing was conducted in two separate years (2006 and 2011) on Interstate 81 in VDOT’s Bristol District. The testing was conducted using the FWD at an interval of 0.2 miles in the right-hand lane (travel lane) of the interstate. The objective of this study was to analyze the results from the 2011 testing and compare them to the results obtained from the 2006 study to determine if the previously completed FWD survey of VDOT’s entire interstate network needed to be repeated. First, deflection values that were obtained from pavement segments that received treatments between the two sets of tests were identified and omitted from any comparison. Second, the two datasets were compared directly (i.e., without accounting for errors) and were modeled to account for the expected errors in the data defined as the root mean square of the difference between 2006 and 2011 measurements. The results of the 2011 testing showed lesser deflection and greater structural number values when compared to the data collected in 2006. A characterization of the errors implicit in each set of measurement showed that the errors outweigh the changes in deflection values from the two datasets. Therefore, it was not possible to quantify a recommended time between subsequent rounds of deflection testing on the pavement network. Since the literature shows significant benefits to conducting pavement deflection testing on the network, VDOT will continue this practice based on local needs and as budgetary constraints allow.