This paper introduces the measurement results on site from a technology named the falling weight deflectometer (FWD) [1]. It is used for non-destructive testing of degraded multi-layered pavement in order to detect the presence of discontinuities, cracks, debounding. This technology can determine with precision the basin of deflection due to a controlled load and can reflect the behaviour of pavement structures. The interpretation of data generated by FWD leans on inverse analysis processes [2]. This data, combined with the thickness of layers, makes it possible to obtain the evolution of the Young's modulus of each layer of the structure along the road profile studied [3]. This information can be also used to estimate its lifespan and possible repairs to be carried out.

A numerical model is also developed, in continuation of precedent works based on the study of the ground - structure interaction [4]. Causal hysteretic damping is taking into account in the elastic behaviour of a multi-layered pavement. The use of Fourier transform in space and time allows an analytical resolution of the problem for a falling load in the case of FWD study, or moving harmonic load in the case of real trafic. The model shows that parameters such as the frequency of excitation and the speed of the load are important. Thus this model has the advantage of taking into account the dynamic aspect of the load whereas in the past the majority of models have rested exclusively on a static analysis.

The resolution of the dynamic problem is also implemented in a finite element code. Results of in situ measurements from the nine sensors (geophones) were compared with the numerical model. The comparison gives promising results, considering the difficulty in characterizing the mechanical parameters of the pavement. From this model, it will be obviously possible to develop an inverse analysis method to characterize the modulus of the layers and to identify the pavement defects.

Finaly, an experimental roadbed is under development in our laboratory. Two types of pavement will be studied, as well as principal defects found in these types of structures. The resulting data could be used to validate the numerical model and will allow the analysis of the wave propagation in multi-layers.

1

J.M. Simonin, "Contribution à l'étude de l'auscultation des chaussées par méthode d'impact mécanique pour la détection et la caractérisation des défauts d'interface", INSA Rennes, thèse de doctorat, 162 p, dec 2005.

2

A. Burak Goktepe, E. Agar, H. Lav, "Advances in backcalculating the mechanical properties of flexible pavements", Advances in Engineering Software, 37, pp 421-431, 2006. doi:10.1016/j.advengsoft.2005.10.001

3

Y.R. Kim, H. Park, "Use of falling weight deflectometer multi load data for pavement strength estimation", NCDOT, Research project HWY-00-4, FHWA/NC 2002-006, 191 p, June 2002.

4

D. Le Houédec, G. Lefeuve-Mesgouez, B. Picoux, "Soil-structure interaction for moving loads : Application to railway traffic", Progress in Civil and Structural Engineering Computing, B.H.V. Topping, (Editor), Saxe-Coburg Publications, UK, pp. 315-344, 2003. doi:10.4203/csets.10.12

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