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

Evolved from the French “deflectometre a 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.

[1]  G Hildebrand.  VERIFICATION OF FLEXIBLE PAVEMENT RESPONSE FROM A FIELD TEST, VOL. 1, 2 AND 3 , 2002 .

[2]  Asli Kurtulus.  Field measurements of the linear and nonlinear shear moduli of soils using drilled shafts as dynamic cylindrical sources , 2006 .

[3]  Jim W. Hall,et al.  Continuous Deflection Basin Measurement and Backcalculation Under a Rolling Wheel Load Using Scanning Laser Technology , 1995 .

[4]  Ernest Zube,et al.  FLEXIBLE PAVEMENT MAINTENANCE REQUIREMENTS AS DETERMINED BY DEFLECTION MEASUREMENT , 1966 .

[5]  Karim Chatti,et al.  Dynamic Time Domain Backcalculation of Layer Moduli, Damping, and Thicknesses in Flexible Pavements , 2004 .

[7]  Andy Collop,et al.  Stiffness reductions of flexible pavements due to cumulative fatigue damage , 1996 .

[8]  Robert Meier,et al.  Backcalculation of Flexible Pavement Moduli from Falling Weight Deflectometer Data Using Artificial , 1995 .

[9]  John T Harvey,et al.  Calibration of Mechanistic-Empirical Models for Cracking and Rutting of New Pavements Using Heavy Vehicle Simulator Tests , 2008 .

[10]  R. Briggs,et al.  Temperature predictions and adjustment factors for asphalt pavement , 2000 .

[11]  R. Al-Khoury,et al.  Spectral element technique for efficient parameter identification of layered media; Part II; Inverse calculation , 2001 .

[12]  R. Al-Khoury,et al.  Spectral element technique for efficient parameter identification of layered media. Part III: viscoelastic aspects , 2002 .

[13]  Sungho Mun,et al.  Fast spectral analysis of an axisymmetric layered structure , 2008 .

[14]  J Simonin.  Contribution a l'etude de l'auscultation des chaussees par methode d'impact mecanique pour la detection et la caracterisation des defauts d'interface , 2005 .

[15]  Johan Blaauwendraad,et al.  Dynamic Interpretation of Falling Weight Deflectometer Test Results: Spectral Element Method , 2000 .

[16]  R. Al-Khoury,et al.  Spectral element technique for efficient parameter identification of layered media. I. Forward calculation , 2001 .

[17]  K Matsui,et al.  STRUCTURAL ANALYSIS ASPHALT PAVEMENT BY FWD AND BACKCALCULATION OF ELASTIC LAYERED MODEL . THIRD INTERNATIONAL CONFERENCE ON BEARING CAPACITY OF ROADS AND AIRFIELDS. PROCEEDINGS, NORWEGIAN INSTITUTE OF TECHNOLOGY, TRONDHEIM, NORWAY, JULY 3-5 1990. VOLUMES 1-2 , 1990 .

[18]  L H Irwin.  Backcalculation: an overview and perspective , 2002 .

[19]  Alain Pecker,et al.  Waves and Vibrations in Soils: Earthquakes, Traffic, Shocks, Construction works , 2009 .

[21]  Karim Chatti,et al.  Dynamic Backcalculation of Pavement Layer Parameters Using Frequency and Time Domain Methods , 2006 .

[22]  Kenneth H. Stokoe,et al.  Estimating Subgrade Stiffness and Bedrock Depth: Combined Falling Weight Deflectometer and Simplified Spectral Analysis of Surface Waves Measurements , 2000 .