The Millau viaduct is a famous cable-stayed bridge located in the Aveyron department, in the Occitanie region. Crossing the valley of the Tarn, the viaduct of Millau ensures the junction between the red causse and the causse of Larzac. This 2460 meter long bridge, built by the company Eiffage, was inaugurated in 2004, after 3 years of work. The Millau viaduct is also the highest bridge in the world at 343 meters and its section of freeway connects Clermont-Ferrand to the city of Béziers, known for its bullring, in just over 3 hours. In this article, we will look at the history of the Millau Viaduct, the birth of the project and the commissioning of this impressive structure that combines elegance and technical prowess.
The history of the Millau Viaduct
The A75 freeway provides a faster link between the north and south of France and also easier access to Spain. Together with the A71 freeway, the A75 also allows to relieve the A7 freeway which crosses Lyon and which is very popular during the summer period. The construction of the A75 freeway, which began in 1975, was completed in 2010. At the same time, the Tarn, a river that flows from east to west in the south of the Massif Central, forms a 200-meter wide gap in some places that is difficult to cross. Before the construction of the Millau viaduct, the crossing was made by a bridge located at the bottom of the valley, in the town of Millau. This caused numerous slowdowns and traffic jams each year during the large summer flows. In addition, these slowdowns meant that all the advantages of the A75 freeway, a 340-kilometre-long freeway that is entirely free of charge, were lost. Similarly, heavy goods vehicles, unable to cross Millau, were obliged to pass through Lyon and via the A6, A7 and A9 freeways. The construction of a viaduct was then envisaged and its implementation required no less than 13 years of studies and consultation before work on it began in 2001.
The technical difficulties associated with the construction of the bridge
The first difficulties are of a technical nature, starting with the exceptional size of the gap to be crossed, i.e. nearly 2.5 kilometers. On the other hand, the violent winds which can reach more than 200 km / hour, as well as the climatic and seismic conditions raise some difficulties of realization. Between 1987 and 1991, the choice of the route of the Millau viaduct is determined among the 4 following options:
- The Grand Est option: this option suggests passing through the east of Millau, but requires the construction of two large bridges, each 800 to 1000 meters long. However, this option is abandoned because it is necessary to use, to serve Millau, the long and sinuous descent known as “cavalry”.
- The Grand Ouest option: longer, this option follows the Cernon valley and is not retained because it is detrimental to the environment of the neighboring villages.
- The option close to the RN9: this option serves the city of Millau well, but presents technical and environmental difficulties.
- The so-called median option: although approved by most of the stakeholders, this option was not retained for geological reasons, particularly due to the crossing of the Tarn valley. The investigations of the experts conclude that it is possible to overcome them: it is therefore this option that will be chosen.
Thus, 5 viaduct options were proposed and finally, the cable-stayed viaduct (a type of bridge whose deck is suspended by cables) was chosen by ministerial decision on June 28, 1989. After long studies, the high solution involving a 2500 meter viaduct passing more than 200 meters above the Tarn was validated. Several associations such as the WWF or France Nature Environnement will oppose the project, as well as the president of the region at the time, the former president of the republic Valéry Giscard d’Estaing. Finally, the Millau Viaduct construction project was declared to be in the public interest by decree on January 10, 1995.
The choice of the structure for the construction of the viaduct
The selected route requires the construction of a 2500 meter long structure. Between 1991 and 1993, CETRA’s civil engineering division, headed by Michel Virologeux, carried out preliminary studies to confirm the feasibility of a structure crossing the Tarn valley. Several design offices and architects are put in competition in order to broaden the search for possible solutions. No less than 17 design offices and 38 architects will apply for the first studies of the Millau Viaduct! In the end, 8 engineering firms and 7 architects were selected for the technical and architectural studies. In February 1994, 5 families of solutions were selected and supervised by 5 pairs of architects/design firms. The characteristics of the work, designed by architect Norman Foster, were finally approved at the end of 1998. At that time, the State, which had to invest 320 million euros, abandoned the idea of a completely free highway. A public procurement notice was launched at the beginning of 2000 and finally, the company Eiffage and its subsidiaries were selected to build the Millau Viaduct. Owned by the State, the Millau Viaduct is financed by private funds within the framework of a concession contract where the expenses of realization and exploitation remain the responsibility of the concessionaire, who in return, is remunerated by the toll revenues. The estimated cost of the entire project is nearly 400 million euros.
The Millau Viaduct: 3 years of construction
The construction of the Millau Viaduct began in 2001 and will take 3 years. Work on the foundations for the 7 piers began in January 2002. With a surface area of 200 m² at the base, the foundations of each pile receive 2000 cubic meters of concrete. At the top, their surface is only 30 m². The abutments (the vaults intended to support the structure of a bridge) were built between March and November 2002. The construction of the piers requires the pouring of 200 cubic meters of concrete every 3 days, allowing the pier to rise 4 meters each time. The verticality of the piles is ensured thanks to laser guides and GPS. On February 21, 2003, pier number 2 exceeded 141 meters, beating the French record held by the Tulle and Verrières viaducts. On June 12, 2003, this same pile reached a height of 183 meters, then 245 meters on October 20. The 7 piers were completed on November 20, 2003. The abutments, 13 meters wide, are intended to receive the deck (the road). The 32-meter wide deck overhangs the Tarn River at 270 meters at the highest point, and accommodates a 2 x 2 lane highway, plus 2 emergency lanes. With its aerodynamic profile, the deck of the Millau Viaduct is able to withstand winds of over 205 kilometers per hour. 7 pylons with a height of 87 meters extend the 7 piers of the structure to which 11 pairs of guy wires are attached. The total weight of steel used in the manufacture of the Millau Viaduct is close to 36,000 tons, which is about 4 times the weight of the Eiffel Tower. A total of 154 guy wires are anchored in the steel structures of the deck and pylons.
The Millau Viaduct in a few figures…
- 13 years of studies were necessary before launching the viaduct construction project.
- 3 years is the construction period between 2001 and 2004.
- 2460 meters long and 32 meters wide.
- 343 meters (maximum height), 19 meters higher than the Eiffel Tower.
- 36000 tons (weight of the deck).
- 206,000 tons of concrete were poured to build the viaduct.
- 7 piers whose height varies between 77 meters and 245 meters.
- 7 pylons with a height of 87 meters each.
- 6 spans of 342 meters (between the pylons).
- 2 spans of 204 meters (at each end of the viaduct).
- 154 shrouds.
- 600 workers worked on the site for the construction.
- 400 million euros: cost of construction.
Guided tours are organized on the explorers’ path to discover the Millau Viaduct from another angle. In addition, an exhibition for the public is proposed near the Millau Viaduct, offering an immersive show as well as exclusive images taken during the construction. All information is available on the website www.leviaducdemillau.com.
