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NDTCE’09, Non-Destructive Testing in Nantes, France, June 30th – July 3rd, 2009

NDT – : Continuum of techniques and applications

Philippe COTE

LCPC – BP 4129 – F44340 Bouguenais Cedex – France [email protected]

Abstract NDT and Applied Geophysics constitute two domains that differ mainly in terms of scale. In order to give a rough delimitation, we can consider that testing objects of dimensions less than one meter is related to NDT while testing anthropogenic objects greater than one meter comes close to applied geophysics. A large number of common techniques for civil engineering applications are applied in both domains, but, the difference of scale seems associated with a separation of stakeholders, that induces the existence of two different communities. Each of them develops its own references and state of the art. The development instrumental devices has followed the most important applications developments. As example for exploration geophysics, seismic reflexion is commonly used and a very large community has developed specific devices and know-how that are refined every day. At the other scale extremity, US scan is used everywhere, every day for a large spectrum of applications. But, at mid scale, for civil engineering applications, these methods are not very frequent. The recent developments of large band sensors associated with adapted vibrators will perhaps fulfil this lack. Some others sonic or seismic techniques are wide scale used. As example, the interpretations of the Rayleigh wave behaviour are observed from millimetric to kilometric scales. At civil engineering scale, these techniques are applied since few years and the number of applications in terms of detection or monitoring increases a lot. Similar comparisons are possible for the electromagnetic or geo-electric domain. Some points relative to scale may complicate interpretations. For example at geophysical scale the celerity of materials is not different than the ones observed at NDT scale but, the observation distances being shorter, the wave trains are less separated at NDT scale. Similar remarks can be made concerning the degree of heterogeneity relatively to wave length. The materials studied at civil engineering scale often present important spatial variations at a scale close to wavelengths that modify signal shape and complicate classical interpretations. As conclusion, several classical techniques are used from physics to millimetric applications. The development of the similar techniques at the civil engineering scale is not always simple either because of a lack of appropriate instruments or because of a greater complexity.

Résumé Les techniques d’évaluation non destructives (END) et la géophysique diffèrent principalement par l’échelle de leurs applications. Grossièrement, les objets inférieurs au mètre sont auscultés par des END alors que les objets anthropiques de taille supérieure le sont via des techniques géophysiques. Les milieux à l’échelle du génie civil sont parfois plus complexes qu’à d’autres échelles. Les variabilités spatiales au regard de la taille des longueurs d’onde sont parfois très importantes ce qui peut complexifier sérieusement signaux et interprétations.

NDTCE’09, Non-Destructive Testing in Civil Engineering Nantes, France, June 30th – July 3rd, 2009

Keywords geophysics, anthropogenic structures, Non Destructive Testing.

References 1. D. Breysse and O. Abraham, (2005), “ Méthodologie d’évaluation non destructive de l’état d’altération des ouvrages en béton”, Presse des Ponts en Chaussées, Paris, France, 555 p. 2. JL. Mari, D. Chapellier, G. Arens and P. Gaudiani (1998), Géophysique de gisement et de génie civil », Editions , Paris, France, 468 p.