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Saint-Flour english summary

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publié le 10 avril 2008 (modifié le 11 avril 2008)

Technical investigation report on the derailing of train 5941 on 25 February 2006 in Saint-Flour (15)

On Saturday 25 February 2006, express train 5941 from Paris to Béziers was running on the single-line stretch of railway between Neussargues and Béziers, and derailed at kilometre point 692,480 in the municipality of Saint-Flour (Cantal county). At this point the line is on a curve with a radius of 296 m, and on a slight slope. The entire train derailed (the locomotive and three carriages), and the locomotive and front carriage were thrown against the rock face.

Two of the passengers were slightly hurt, while the rolling stock and 100 m of infrastructure were seriously damaged.

The direct cause of the accident was a broken rail on the outside of the curved line, at a thermit weld. Periodic ultrasound checks had detected no precursory signs of a fault in the rail. The break, together with the loss of a fastener, led to a significant mismatch between the two detached ends, causing the train to derail at this point.

At the root of the accident were the fact that the line was obsolete and an inadequate maintenance policy.

The line, which is equipped with “bullhead” rails, is prone to causing derailments in the event of a rupture, and replacement parts for these “ancient” rails are no longer available. Moreover, the wider sleeper spacing contributes to an increase in the stresses exerted on them. Lastly, the gradual removal of ballast over time has made it impossible to maintain the line at the correct level.

Maintenance policy rules out any form of regeneration (“continuous surface” method). Thus, the number of welds on the line has increased to compensate for the lack of rail replacement, creating fragile points, and the one-off replacement of individual wooden sleepers has brought about a displacement phenomenon, because it is impossible to add re-levelling ballast.

These observations lead us to formulate the following recommendations :
- in the short term, a methodology should be set out to mark out the “special zones” in which train speed should be reduced to prevent derailments in the event that “bullhead” rails rupture.
- replacing the rail, wherever possible, with a continuous bar instead of carrying out welding. This measure would firstly require still-healthy “bullhead” rails to be obtained,
- the set-up of a programme to re-level the lines equipped with “bullhead” rails, in which the replacement of sleepers should be accompanied by the addition of ballast,
- in the long term, the replacement of the “bullhead” rails with Vignole rails.