Millau Viaduct

The Millau Viaduct is a cable-stayed bridge that crosses the Tarn Valley, in the department of Aveyron, France. The structure supports a section of the A75 motorway, allowing the connection between the causse Rouge and the causse du Larzac as it crosses a gap 2,460 meters long and reaches 343 meters at its highest point, where the wind can blow at more than 200 km/h.

Development of national and international importance, the link connects Clermont-Ferrand to Béziers. This project required thirteen years of technical and financial studies. Studies began in 1987 and the structure was put into service on December 16, 2004, three years after the foundation stone was laid. At a cost of €320 million, it was financed and produced by the Eiffage group as part of a concession, the first of its kind, for its duration of 78 years, including three of construction.

At the end of the 2010s, it had a traffic of more than 4.5 million vehicles per year.

History

Construction of the board by launch

The Millau Viaduct was designed by French engineer Michel Virlogeux and British architect Norman Foster. The names of the approximately 530 people who worked on the project were entered into a copper cylinder that was buried in pylon number three. Construction began on October 10, 2001 and was to last three years, being inaugurated in December 2004 after 36 months of work.

At the time it constituted the greatest challenge in France for engineers and architects since the construction of the Normandy Bridge. During preliminary studies four options were considered:

1. Roll Millau east, which would require two large bridges over the Tarn and Dourbie.
2. Roll Millau in the west, traveling a total of 12 km, which would require the construction of four bridges.
3. Follow the route of National Route 9, which would provide good access to Millau but would involve technical difficulties, as well as crossing the population.
4. Cross the valley in the middle.

This fourth option was chosen by the government on June 28, 1989. In turn, it contemplated two different possibilities: the elevated solution, and the low solution, which would imply the construction of a 200 m bridge to cross the Tarn, followed by a 2,300 m viaduct extended with a tunnel on the Larzac side. After long feasibility studies, the low solution was discarded due to its higher cost.

Once it was decided that the solution would be the elevated one, five groups of architects and engineers worked simultaneously in search of a technical solution. First, the piers that would support the pylons in the final configuration of the bridge were built. The construction of the deck was carried out at the ends. Using this technique, and as the cross sections are built, the deck is periodically pushed onto the piers, leaving space for the placement of new bridge sections. To avoid large overstresses that would force the section to be excessively reinforced with respect to the service phase, a series of intermediate shorings were arranged so that the spans were shorter during the construction phase. Once the deck was pushed from both ends and reached the point of union, both halves were assembled and the guying towers were placed. Finally, the provisional shorings were removed.

Drivers were initially able to cross it by paying €4.90, but from the following summer the fare rose to €6.50.

The viaduct exceeded the height of what was until then the highest bridge in the world, the Europe Bridge, in Austria. It also became the highest road bridge if road level is taken as a reference. The height of 270 meters at which it is located, exceeds the 268 meters of the bridge over the New River Valley, in West Virginia, United States. However, in this section, the 331-meter Royal Gorge Bridge over the Arkansas River exceeds the Millau Viaduct, but in that case it is a pedestrian crossing.

Features

Location.

The structure reaches a maximum height of 343 meters above the Tarn River, and a length of 2460 m, between the Cause del Larzac and the Cause Rouge; it has seven concrete piers, and the deck is 32 meters wide. The highway has a 3% grade, descending in a north-south direction, and curves in a flat section with a radius of 20 km. The latter was done with the intention of giving motorists better visibility. It has two traffic lanes in each direction.

It is made up of eight sections of steel deck, which rest on seven concrete piles. The causeway weighs 36,000 tons and stretches for 2,460 meters, with a width of 32 m and a thickness of 4.3 m. The six internal sections of the viaduct are 342 m long, while the two ends measure 204 m. The pillars are between 77 and 246 m and go from having a longitudinal section of 24.5 m at the base to 11 m at the top. Each pier is in turn made up of 16 sections, each weighing 2,230 tons, and in total the bridge weighs around 350,000 tons. These sections were assembled on site from parts that were manufactured in Lauterbourg and Fos-sur-Mer by the construction company Eiffage, first being assembled together with temporary supports, and prior to the installation of the beams, which were arranged at a rate of 600 millimeters every four minutes.

Builders

General view of the viaduct, with the city of Millau on the left.

The construction company that won the contract to build the viaduct was the Compagnie Eiffage du Viaduc de Millau. The construction consortium was made up of the Eiffage TP company for the concrete sections, the Eiffel company for the laying of the steel sections and the Enerpac company, which was in charge of the hydraulic supports for the highway.

The engineering group Setec assumed responsibilities in the project, while SNCF had partial control of it.

In the tender, three other consortiums bid to obtain the contract:

• The first, led by the Spanish Dragados, in association with Skanska (seven) and Bec (French).
• The Société du viaduc de Millau, composed of ASF, Egis, GTM, Bouygues Travaux Publics, SGE, CDC Projets, Tofinso (French all) and Autostrade (Italian).
• A third consortium, led by Générale Routière, with Via GTI (French prawns), together with Cintra, Necso, Acciona and Ferrovial Agroman (Spanish).

The original conceptual and structural design of the bridge is the work of Frenchman Michel Virlogeux; while the architects responsible for the aesthetic and formal aspects of the work belonged to the British company Foster and Partners, led by Lord Norman Foster. Along with the above, was the Dutch engineering firm Arcadis, responsible for the technical design of the viaduct.

The project used 127,000 m³ of concrete, 19,000 metric tons of steel for the concrete reinforcement, and 5,000 tons of prestressed concrete. The construction company also has a 120-year concession for its maintenance.