Review Ground-penetrating radar for the structural evaluation of masonry bridges: Results and interpretational tools M. Solla ⇑ , H. Lorenzo, F.I. Rial, A. Novo Department of Natural Resources & Environmental Engineering, University of Vigo, A Xunqueira, 36005 Pontevedra, Spain article info Article history: Received 29 November 2010 Received in revised form 31 August 2011 Accepted 2 October 2011 Available online 29 November 2011 Keywords: Non-destructive evaluation GPR FDTD modelling Masonry structures abstract Ground-penetrating radar (GPR) has shown good potential in providing valuable information for the eval- uation of masonry structures. We used GPR to survey several stone arch bridges located in the Galician territory in Spain. The results revealed previously unknown geometrical data and hidden characteristics of the interiors of the bridges, including the presence of internal voids, ancient arches, and restorations. However, many factors can adversely affect a GPR survey, such as ringing noise and signal attenuation. These factors can make data interpretation complex. To assist in the interpretation, we employed numer- ical modelling because it can play a very important role in extracting valid and useful information from GPR data sets. The expected electromagnetic wave response can be simulated through the use of model- ling tools. The obtained information can be useful for engineers, as it provides better structural knowl- edge of the bridge. Ó 2011 Elsevier Ltd. All rights reserved. Contents 1. Introduction ......................................................................................................... 458 2. Methodology......................................................................................................... 459 3. Results and discussion ................................................................................................. 461 4. Conclusions .......................................................................................................... 464 Acknowledgments .................................................................................................... 464 References .......................................................................................................... 464 1. Introduction Ancient stone masonry arch bridges are still commonly in use within the transport infrastructure. Many of these structures re- quire special attention and monitoring. Increases in traffic load and intense vibrations since they were designed can result in struc- tural decay [1,2]. Therefore, ongoing diagnosis of their changing structural integrity is required to provide information to help with their preservation and restoration. In the last several decades, there has been a continuous increase in the use of non-destructive testing (NDT) to evaluate civil engi- neering structures [3,4]. Ground-penetrating radar (GPR) is an NDT method that is used for evaluating masonry bridges [5]. Nev- ertheless, there have been are few published studies on testing stone masonry bridges using GPR, with some notable exceptions [6–12]. These studies have provided promising information about the hidden geometry, bridge foundations, ring stone thickness, moist zones, and fill conditions in masonry bridges. There are many stone arch bridges in the Autonomous Community of Galicia (northwest Spain) [13]. For this work, we studied 36 stone masonry arch bridges located in the Galician ter- ritory (Fig. 1). Our objectives were to analyse the viability and effectiveness of GPR in obtaining previously unknown, inner de- tails for the assessment of these structures. The knowledge of this structural information is important for civil engineers engaged in developing future conservation and strengthening techniques. Many factors can adversely affect GPR waves, including ringing noise, airwave events, and signal attenuation. Data interpretation can become complex because of these unfavourable events. There- fore, several factors should be taken into account to improve the interpretation of the GPR data. These factors include the establish- ment of survey objectives, compilation of all available structural and geometrical information about the bridge, and knowledge of 0950-0618/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.conbuildmat.2011.10.001 ⇑ Corresponding author. Tel.: +34 986 801908; fax: +34 986 801907. E-mail address: merchisolla@uvigo.es (M. Solla). Construction and Building Materials 29 (2012) 458–465 Contents lists available at SciVerse ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat