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Assessment of flexible airfield pavements using Heavy Weight Deflectometers. Development of a FEM dynamical time-domain analysis for the backcalculation of structural properties.

Abstract : Evolved from the French “déflectomètre à boulet”, the Heavy Weight Deflectometer (HWD) is today viewed worldwide as the most appropriate device to assess the bearing capacity of airport pavements. Its principle consists in applying a transient impulsive load simulating the weight effect of an aircraft rolling wheel, onto a stationary load plate placed over the pavement, through a buffer system, and studying the surface deflections induced by this dynamic loading. The latter are continuously measured during the test by means of geophones. These deflection measurements are used to determine the structural properties of the pavement, by means of a “backcalculation” numerical procedure which consists in: 1- choosing a mechanical model for the pavement, 2 - identifying the parameters of the model for which theoretical computed deflections fit the experimental data set. Then, forward calculations can be performed to estimate the bearing capacity or the remaining life of the structure. Usual processing methods for the assessment of flexible pavements are based on static multilayered elastic models. The structural properties to be backcalculated are the stiffnesses of the different layers. The backcalculations are performed from pseudo-static deflection bowls reconstituted from the deflection peak values measured by each geophone. As emphasized by several authors, these methods have shown limitations. Indeed, they use only part of available information (peak values), and the static modelling is far from the reality of the test. The objective of the thesis was to develop an advanced method for the assessment of flexible pavements using HWD tests data which achieves a better representation of the observed physical phenomena during dynamic loading and allows taking into account the whole available information. A time-domain FEM modelling has been developed, where the applied dynamical load, inertia of materials and structural damping are modelled. It allows the computation of ensuing time-related deflections. An automated convergence algorithm has been developed for numerical resolution of the backcalculation procedure. A full-scale validation of both backcalculation method and strains determination has been conducted. It consisted in test surveys run on a reference instrumented pavement. The validation has relied on the comparison between backcalculated and laboratory-determined material properties, and on the comparison between expected strains and measured strains. A numerical tool has been developed which allows automating the finite elements mesh creation and both backcalculation and forward calculation phases: the PREDIWARE (Pavement Rational Evaluation using Deflections Induced by Falling Weights, for Airfield and Road Engineers) software.
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Submitted on : Monday, February 14, 2011 - 2:09:50 PM
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Michaël Broutin. Assessment of flexible airfield pavements using Heavy Weight Deflectometers. Development of a FEM dynamical time-domain analysis for the backcalculation of structural properties.. Mechanics of materials [physics.class-ph]. Ecole des Ponts ParisTech, 2010. English. ⟨NNT : 2010ENPC1008⟩. ⟨pastel-00565757⟩

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