Improved Moduli Backcalculation of the Upper Layers in Asphalt Pavements

This study was motivated by the need for improved moduli backcalculation of the upper layers in asphalt pavements. The method of improvement was to physically upgrade the usual falling weight deflectometer (FWD) design to host an extra geophone at a nontraditional offset of 100 mm, i.e., within the loading plate. A synthetic investigation was carried out first to assess the idea, which found that the extra geophone elevates the FWD’s sensitivity to moduli changes in the upper portion of the pavement and offers new and meaningful deflection information. Next, device upgrades were designed and implemented in an existing FWD, transforming it to a so-called FWDt prototype. Field testing with the new prototype demonstrated that the extra geophone measures correctly and that the added deflection data benefit backcalculation results by guiding the optimization process to distinguish between otherwise competing moduli sets. The overall conclusion is that improved moduli backcalculation, especially of the upper layers in asphalt pavements, is enabled by the FWDt. At the same time, and given the early development stage of this device, further theoretical and experimental research is recommended to better appreciate its engineering utility.