The viaduct of Garabit is a railway work located close to Ruynes (not far from Saint-Flour) in the Cantal, which allows the Ligne Causses to cross the throats of the Truyère, affluent of the Lot. Entirely Metal lic, it was built by the company Gustave Eiffel & Co and was completed in 1884, but the startup of the line took place only in 1888.

The viaduct of Garabit is composed of long steel deck a 564,85 m resting out of seven piles in Fer puddled variable height (up to 80 m for two higher). The three spans located above the lowest part of the valley are supported by a arc of a range of 165 m and a height of 52 Mr. the metal part is framed by two viaducts of northern and southern access, in masonry, of 46 m and 71 m respectively. The height above the low water level of Truyère was of 122,5 m, however since construction in 1959 of the Barrage of Grandval on Truyère, which involved the formation of a Lac of reserve 28 km length, the Viaduc overhangs the lake of 95 Mr.

At the origin of the project, the idea of a metallic bridge with large arc spanning the valley returns to a young person Engineer, Leon Boyer, born in 1851 and prematurely dead in 1886. It is him which imposed the idea of a direct layout on the plates and a crossing of Truyère on great height (120 m above the level of low water level), rather than the traditional solution which would have consisted in descending the line by the tributary valleys to cross Truyère by a more modest work, more expensive solution in exploitation thereafter.

For this crossing, it was excluded to resort to the Suspended bridge, because of the risks of oscillations, and it was impossible to consider at the time of the piles of more than 65 m in height. Leon Boyer took as a starting point the example of the Viaduc Maria Pia on the Douro (Portugal). This viaduct also builds by the house Eiffel had been designed by another associate of Eiffel, Theophilus Seyrig, and had been inaugurated in 1877. It comprises a metallic arc of 160 m range, with an arrow of under-surface of 37,50 Mr.

The viaduct of Garabit in figures

• Overall length of the apron: 564,69 m
• Carried principal Arch: 165 m
• Height above the low water level: 122 m
• Volume of Masonry: 20.370 m ³
• Quantity of metals employed:
• Wrought iron: 3169 T
• Steel: 41 T
• cast iron: 23 T
• Nombre of rivets posed: 678.768
• Lasted of the building site: four years (of January 1880 in September 1884)

Chronology

• November-December 1878: Leon Boyer carries out liftings on the ground to define the layout of the line
• March 25th 1879: the first project drawn up by Leon Boyer is given to the administration
• June 14th 1879: the public Ministry of Labor approves the project;
• January 1880: beginning of work
• August 16th 1880: Gustave Eiffel files in the final draft
• 1882: beginning of the assembly of the piles
• April 20th 1884: pose key of under-surface
• April 26th 1884: pose key of suction face
• June 1884: end of the pushing of the aprons
• September 17th 1884: completion of the vaults of the viaducts of access and the installation of the way
• May 9th 1887: opening of the line Marvejols - Saint-Chély-with Apcher
• April 10th 1888: first tests of the viaduct in load
• May 26th 1888: opening of the line Saint-Chély-in Apcher - Saint-Flour
• November 10th 1888: complete opening of the line.