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Description
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This research work had the aim of developing a procedure for back-calculating accurate and precise parameter values, describing the mechanical behaviour of the materials built in an existing road structure. After reviewing the existing testing techniques, a new device was designed and assembled at the IGT, Institute for Geotechnical Engineering (ETH Zürich) for measuring the three dimensional deflection bowl under a standard axle load (SAL). Particular attention was paid for obtaining precise and accurate significant measurements for inverse analysis. Three field tests on different locations and road structures were carried out: a flexible pavement type built in a concrete pit (indoor facility) at the EPFL (Ecole Polytechnique Federale de Lausanne), a semirigid type in Hinwil (Switzerland) and a flexible type in Bellinzona (Hinwil). The tests results show that the measured road displacements under a SAL, for relatively low temperatures, are generally reversible and time independent. Laboratory tests (uniaxial compression) were carried out on cores obtained from field samples.
The strain measurements of the loaded samples were carried out with strain gages, and validated against devices with different technology (LVDT). The analysis of the test results showed that the materials have different bulk and deviatoric stress-strain behaviour. A new thermodynamical framework for non linear viscoelasticity (hyperviscoelasticity) was developed. Experimentally validated hyperviscoelastic and hyperelastic constitutive laws were adopted respectively for describing the mechanical behaviour of asphalt and cement stabilized mixtures. The inverse analysis of the field tests results was carried out with two different optimization algorithms (Levenberg Marquardt and Mesh Adaptative Direct Search), the FE program ABAQUS, and the developed user defined models. The results demonstrate the accuracy and precision of the parameter values obtained with the proposed inverse analysis procedure, demonstrating a potential for application of the developed technique for non destructing testing of real road structures.
