Millau Viaduct Construction Issues and Challenges.

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• published: 23 Jan 2011
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An extraordinary story for an exceptional construction From the first sketches in 1987 to the completion of work in 2004, it took seventeen years of research and work to fill in the missing link in the A75. The Millau viaduct, which some call the "pont du Gard" of the 21st century, completes a multitude of steps. For each one, rigour, precision and professionalism were the key words. There were many essential conditions to make this exceptional construction one for the record books. Fourteen months of preparation for a unique adventure 1987: the first sketches of the tracing of the A75 motorway to link the Causse rouge, to the north, to Larzac, in the south, are begun. Several proposals are put forward for crossing the Tarn valley, to the east and west of Millau. 1994: the decision is taken. A bridge will be built a few kilometres downstream of the town. 1996: following a call for tender, the solution designed by Michel Virlogeux, head engineer at the Ponts et Chaussées, drawn by Sir Norman Foster, architect, was selected. A multi-stay cabled construction will be seen on the Aveyron skyline. Its aesthetic aspect and integration into the countryside attracted the government departments. It took preference over four other potential projects: a bridge of constant thickness, a variable thickness bridge, a viaduct with stays stretched under the deck and a construction with one single arch. 1998: the government grants the concession of the construction and management of the viaduct. This is fixed for a period of 75 years. 2001: in October, following a call for tender, the alliance of concrete (pier) and steel (deck) recommended by the groupe Eiffage received state approval. Concrete has all the endurance qualities required. Steel allows for the construction of a thin, lightweight deck. On 14 December, the adventure begins with the laying of the first stone. Three years for a gigantic worksite Concrete... By spring 2002, the first piers of the Millau viaduct were rising skywards. At the same time, the anchorage points of the deck (the abutments) were appearing in the causses. A few weeks were all it took to carry out the earthworks. Twelve months after the work began, the pier "P2" went above 100 m. A year later, on 9 December 2003, the concrete work was completed on time! And what's more, the record for the tallest pier in the world was set at 245 m. Steel... Assembling the steel deck began in the summer of 2002. Two open-air sites were set up just behind the abutments. On 25 March 2003, a first section of deck (171 m) was driven out into open space: this rolling out operation was a success. 17 others followed suit, at an average rate of one rolling out every four weeks. On 28 May 2004, at 14:12 exactly, the junction -- or "clavage" -- of the north and south sections of the deck took place 270 m above the Tarn. Mission accomplished ! And then the rest... On 29 May 2004, 24 hours after the junction, the installation of the pylons began, followed by the placing of 154 stays to support the deck. In three months, it was all completed. At the end of September 2004, the surface was laid on the deck. The road surface (paint, safety devices, etc.), installation of the safety systems, lighting, finishing touches to the tollgate: everything was ready on 16 December 2004 for the commercial running of the viaduct.