Voie ferrée

Résumé

Une voie ferrée est un chemin de roulement pour trains constitué de deux files de rails dont l'écartement est maintenu constant par une fixation sur des traverses, reposant elles-mêmes sur du ballast. Historique Le terme de voie ferrée apparait à partir du en Angleterre et désigne à l'époque l'agencement de deux rails de bois parallèles sur lesquels un cheval tracte une cargaison, ce qui augmente la vitesse du transport. En effet, les rails sont plats contrairement aux routes à l'époque cabossées, et le problème des virages et intersections ne se pose plus puisque le cheval et la cargaison suivent toujours le même chemin. La voie ferrée ne sert alors qu'au transport de fret. À partir de 1820, les rails sont construits en fer et le bois disparait peu à peu de l'infrastructure, à l'exception des traverses. Ce n'est qu'à partir de 1830 que les voies ferrées servent peu à peu au transport de voyageurs.

Source officielle

https://fr.wikipedia.org/wiki/Voie_ferr%C3%A9e

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Renewal of a fixed railway track using UHPFRC - first use worldwide of UHPFRC in rail track construction, part 1

Antonina Hochuli

This two-part article reports on the renewal and adaptation of the fixed railway track in the heavily frequented underground train station at Zurich Airport. The fixed track built in 1980 had reached the service duration predicted by the system provider and was showing damage. In order for the platforms to meet the requirements for people with disabilities, the track geometry had to be adapted in sections by lowering. For this reason, a simple exchange of the sleeper blocks was not possible and a special solution was required. With the use of the Ultra-High-Performance Fiber Reinforced Cement-bound composite building material UHPFRC, a sustainable and economical solution was found for a project in which a traditional solution would have been time-consuming and costly. In addition, it was found within the scope of this project that the use of UHPFRC with significantly improved mechanical properties increases the service duration of the fixed railway track. With the use of UHPFRC, the service duration of the fixed railway track becomes equal to the one of the whole train station, which further improves economic efficiency.

ERNST & SOHN2021

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2012

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The geometry of the railway track is degraded under traffic load, and must be maintained periodically. This degradation is due to the arrangement of ballast particles under loads and vibrations, which results into irreversible plastic settlements. Tamping is a procedure of maintenance, used to restore the correct geometrical position of the ballasted tracks. However, the penetration of the vibrating tines into the ballast causes an increase in the fine particles content by rupture of the edges of the grains and leads to a progressive degradation of the ballast and thus to a loss of its mechanical properties. The main consequence is that the interval between two tamping operations decreases, along with the long-term effectiveness of the process. This vicious circle can be broken only by ballast renewal. Ballast and geometry maintenance represent 40 to 50% of the total railway maintenance budget during lifetime. The goal of this research is a better understanding of ballast degradation and the development of a tool to evaluate the effectiveness of the track tamping, according to the ballast condition and the infrastructure stiffness. This knowledge will make it possible to decrease the destroying effects of tamping over ballast and, consequently, increase the durability of track geometry and ballast. A full-scale laboratory study has been done on ballasts and infrastructures of different qualities. The dynamic loading of freight trains is simulated with a big hydraulic actuator, while the deformations of the track and his infrastructure are continuously measured. The accelerated loading corresponds to a period of 20 years of traffic operation on a high loaded line. Empirical settlement laws are written, based on the traffic results. Tamping process is performed with a special machine, which was built by purpose. The parameters to regulate tamping process can be controlled. The whole process and the equipment are completely instrumented, in order to control and measure several parameters in real time. The evolution of the ballast behaviour is analysed with the measurement of the bearing modulus. Plate load tests are performed under specially equipped sleepers, after each traffic cycle and tamping. The parameters of a new tamping are tested. The short and long-term effects on ballast are analysed and discussed. A two-dimensional finite element model has been applied to simulate the response of the ballast layer under traffic loading, and the development of settlements. Ballast at different degradation levels is studied. The influence of the subgrade stiffness is also taken in account. The elastoplastic Hujeux behaviour law is applied, in order to study the cyclic plasticity. Results are presented and the critical zones, which show the most plastic behaviour, are identified. A phenomenological model is also developed to analyse separately the effects of traffic loading and track tamping on ballast behaviour and degradation. This analysis is based on a backcalculation approach, and is performed on a 3-D finite elements model of the track. The Young modulus of the ballast and the infrastructure layers in situ is calculated by iteration. Along with the traffic simulation, the evolution of the ballast elastic modulus is measured. A comparison between two sections with different infrastructures is done.

EPFL2010

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EPFL2010