Falling-Weight Deflectometer Study: Optimizing the Number of Replicates and the Spacing of Test Stations

The Strategic Highway Research Program, managed by the Federal Highway Administration, includes a pavement evaluation component as part of its Long-Term Pavement Performance study. These evaluations include the use of falling-weight deflectometer (FWD) test devices. The purpose of this project was to determine whether the FWD test procedures could be modified to reduce cost, without losing a significant amount of information. Procedural changes could include a decrease in the number of test replicates and/or an increase in the spacing between test stations. Variability between replicates was found to be relatively low; a reduction in replicate drops from four to two would not cause a substantial loss in information. An increase in spacing between tests from 7.6 m (25 ft) to 30.5 m (100 ft) would result in a substantial loss of information. An increase in spacing from 7.6 m (25 ft) to 15.2 m (50 ft) would be reasonable if test section responses to FWD were to be summarized as expected values and dispersions. If extremes in pavement response (e.g., miminum and/or maximum stiffness) were judged to be the most important results, the spacing between tests should not be increased from 7.6 m (25 ft).