Keywords: dynamic analysis, non destructive control, finite elements, multilayered structure, flexible pavement, falling weigh deflectometer, damage, deflection basin analysis.

The falling weight deflectometer (FWD) is a control device used for non-destructive evaluation of flexible pavements [1]. The deflection measured by nine geophones from the FWD enables the layers pavement modulus to be estaimated by using backcalculation programs [2]. Most of these programs use the finite element method to calculate the pavement structural response. Although the backcalculation of the whole multi-layered structure is often very complex and based on several parameters, the information selected are reduced to maximum deflections. The maximum values as a function of distance which represent a basin of deflection are considered representative of the pavement structural capacity. A numerical optimization process is used so that the deflections provided by a pavement model agree with this deflection basin. Several methods take into account the interface state between two layers. However, most of them do not take into account pavement damage, such as interface flaws and cracks. The problem rests on the ability to detect these defects in a damaged pavement. There are some pavement testing techniques for the detection of damages, but most are limited to their field of application, by their performance. Among these methods, the measurement of the radius of curvature is the most operational way in the pavement area.

This paper includes a dynamics study of the mechanical behavior of the flexible pavements. The model developed is a two-dimensional axisymmetric finite element model. The different layers are considered to be homogeneous, isotropic and linear elastic. First, interfaces are considered to be perfectly bonded, then we studied the case of a damaged pavement (asphalt concrete interface flaws and cracks). The dynamic model takes into account the asphalt concrete sensitivity towards temperature. The comparison of our numerical results with other models [3] as well as in situ FWD tests [4] provides satisfactory results and allows the validation of the numerical model. To explore the possibility of detecting interface defaults in damaged pavements with the use of a simple FWD test, several criteria can be used: the basin of deflection, its first and second derivatives.

A platform testing conducted by the GEMH laboratory (University of Limoges), in which we have simulated defects (interface flaws, cracks) allowed us to compare the numerical results and verify the effectiveness of the methods proposed to detect damage from the FWD data.

1

Hakim B., Brown S.F., "Pavement Analysis Using the FWD : Practical Difficulties and Proposed Simplification", Proceeding of the 10th International Conference on Asphalt Pavement, Quebec City, Canada, 2006.

2

Burak Goktepe A. et al., "Advanced in backcalculating the mechanical properties of flexible pavements", Advances in Engineering Software, 37, 421-431, 2006. doi:10.1016/j.advengsoft.2005.10.001

3

Loizos A., Scarpas A.T., "Verification of falling weight deflectometer backanalysis using a dynamic finite elements simulation", The International Journal of Pavement Engineering, Vol. 6, No. 2, 115-123, June 2005. doi:10.1080/10298430500141030

4

B. Picoux, A. Millien, C. Petit, A. Phelipot-Mardelé and L. Ulmet, "Diagnosis of a Flexible Pavement using Falling Weight Deflectometer Technology and Numerical Modelling of Dynamic Response", in Proceedings of the Eleventh International Conference on Civil, Structural and Environmental Engineering Computing, B.H.V. Topping, (Editor), Civil-Comp Press, Stirlingshire, United Kingdom, paper 184, 2007. doi:10.4203/ccp.86.184

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