Railway vibrations induced into the soil: experiments, modelling and isolation
AbstractRailway traffic induces cyclic and dynamic loadings in the track structure but also in the close environment (Degrande et al., 2006;François et al., 2007;Kausel, 2008;Lefeuve-Mesgouez et al., 2002;Paolucci et Spinelli, 2006). The analysis of such excitations and their effects (e.g. vibrations, waves, etc.) is fundamental to estimate their level and mitigate their potential consequences (settlements, nuisances, etc.). After a brief summary of the current regulations, in situ experiments show the variability of the parameters characterizing the main phenomena (wave propagation into the soil, induced vibrations, etc.). The main dynamic laboratory experiments are then discussed. They allow the estimation of the dynamic features of the materials (e.g. resonant column test), but also a simplified analysis of the main phenomena under controlled conditions (e.g. experiments in a geotechnical pit, centrifuge tests). The vibratory sources and the impedance ratios between the various soil layers (or some inclusions) being known, it is then possible to model some specific or actual configurations through theoretical (transfer functions) or numerical (e.g. finite elements, boundary elements) methods. Parametric studies allow the analysis of the propagation phenomena and the attenuation process in the soil in order to investigate the spatial variations of the vibrations amplitude in such various configurations. Finally, it may be useful to consider mitigation or isolation techniques in order to limit the consequences of the induced vibrations (e.g. vibratory nuisances, radiated noise). Several experimental and numerical results illustrate this key issue.
La mesure du module de déformabilité, plus classiquement appelée portance, sur les plates-formes d’infrastructures est un élément clé de l’assurance qualité. La co-existence de matériels de mesures différents est une réalité fréquente sur chantier et la tentation de faire des essais croisés pour tester ou valider les performances réciproques des matériels est forte. Les résultats présentés ici ont montré que la dispersion en un point donné est liée au corps d’épreuve et l’emporte sur l’exactitude des appareils de mesure que les auteurs ont testés (Plaque et Dynaplaques). Il est donc inutile de réaliser des essais croisés sur chantier avec ces deux type d’appareils car ils donnent sur un grand nombre de mesures les mêmes résultats. Les appareils de mesure doivent être utilisés en priorité, et en toute connaissance de leurs limites, comme des outils de détection d’anomalies sur une plate-forme. La multiplication des points de mesure améliore la connaissance des hétérogénéités de la plate-forme.
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