Comparative FWD measurements at BASt

The Falling Weight Deflectometer (FWD) is used worldwide to measure the bearing capacity of road pavements. To ensure the quality of these measurements, the German Federal Highway Research Institute (BASt) has been conducting annual comparative measurements for FWD operators since 2015.

FWD’s in action

The comparability and repeatability of the deformation measurements is checked at 21 measuring points on the BASt site for each FWD. In addition to the purely technical comparison, the measurements are used for the exchange of experience between the measuring equipment operators, which BASt considers to be an equally important component of quality assurance.

Participation in the comparison measurements is possible for every operator. The participants come from Germany, but also from many European countries. In 2022, 14 FWD operators with 17 FWD were participating – from Germany, Poland, the Netherlands, Switzerland, Latvia, Denmark and Estonia.

The required precision of an FWD to measure minimal deformations needs a system of quality assurance from standardized calibrations on test rigs, repeated self-monitoring of the FWD operator as well as from participation in comparative studies. One of BASt’s original tasks is to perform such tests or to create the basis for performing them. Since the BASt itself operates two FWD and chairs the “bearing capacity” working group of the Forschungsgesellschaft für Straßen- und Verkehrswesen e. V. (FGSV), the BASt initially tested the performance of comparative measurements on a small scale. Over the last few years, the BASt comparative measurements have become established internationally, and participation in them is still voluntary in Germany.