Multi-directional Falling Weight Deflectometer (FWD) testing and quantification of the effective modulus of subgrade reaction for concrete roads

ABSTRACT

Falling Weight Deflectometry (FWD) tests are performed around the centres of two rectangular concrete plates, with geophones measuring vertical deflections in eight directions. Experimental results allow for quantifying asymmetries regarding the structural behaviour. Significant asymmetries are found for a 22-year-old plate scheduled for replacement. A new plate, tested a few weeks after production, is found to behave in a virtually double-symmetric fashion. Structural analysis of the new plate is based on Kirchhoff–Love plate theory, using free-edge boundary conditions. The support of the plate is provided by a Winkler foundation. Performing a static analysis, the uniform modulus of subgrade reaction is optimised to reproduce the measured deflections. The result is not convincing. The model is extended towards consideration of a second optimisation variable: a uniform auxiliary surface load. This allows for reproducing the measured deflections. The auxiliary load is superimposed with the pressure resulting from the Winkler foundation. This yields a realistic distribution of subgrade pressure. Dividing it by the deflections results in the distribution of the effective modulus of subgrade reaction. Finally, the analysis is extended towards the consideration of inertia forces. They increase the effective moduli of subgrade reaction determined by means of static analysis by less than 3.5%.

KEYWORDS:

• Field testing
• concrete
• modulus of subgrade reaction
• static analysis
• dynamic analysis
• FWD

Acknowledgments

Help of Pia Mandahus (TU Wien, Vienna, Austria), Marek Milcevic, Roman Oblak and Harald Aigner (Nievelt Labor GmbH, Höbersdorf, Austria) as well as interesting discussions with Wolfgang Kluger-Eigl and Luis Zelaya-Lainez (TU Wien), Martin Peyerl and Gerald Maier (Smart Minerals GmbH, Vienna, Austria) as well as Reinhard Lohmann-Pichler and Karl Gragger (ASFINAG Bau Management GmbH) are gratefully acknowledged.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This research received financial support by the Österreichische Forschungsförderungsgesellschaft [Austrian Research Promotion Agency (FFG)], the Austrian Ministry for Transport and Technology (bmvit), ÖBB-Infrastruktur AG (Vienna, Austria), and ASFINAG Bau Management GmbH (Vienna, Austria), within VIF-project 2015 ‘STRUKTurelle Zustandserhebung und -bewertung von Betondecke (CONcrete) auf Projektebene – ConSTRUKT’ and the Bridge Project 2021 ‘Grundlegende Analyse von FWD-Versuchen: innovative Experimente, moderne Struktursimulationen, statistische Datenanalyse – FALLINGweight’. The authors also acknowledge the TU Wien University Library for financial support through its Open Access Funding Programme.