Along the Tarn Valley in France history is being built: a bridge that will span 1 1/2 miles of valley, soaring 1,000 feet above the River Tarn. The Millau Viaduct bridge will be the world’s highest when completed in 2005.
When the French engineering team Foster was awarded the project in 1996, employees knew it would be no small task. Their design, which calls for seven piers that range in height from 200 to over 1,000 feet, is expected to use more than 35,000 cubic yards of concrete, 17,000 tons of concrete-reinforcing steel and over 4,000 tons of steel strand and coverings. About 1,100 feet are between each of the piers, and masts extend 300 feet above the road deck. With the center pier exceeding 1000 feet, the bridge is expected to be 14 percent taller than the Eiffel Tower.
One of the most difficult construction issues the project has faced is how the steel-reinforced concrete deck will be placed. The deck, which will be held up by suspended cables, will weigh over 32,000 tons and will be wide enough for six lanes of traffic. Engineers hope to ease the complication by prefabricating the deck spans at a different site. The deck spans will then be transported and lifted by a combination of 64 Enerpac hyraulic cylinders, which have a pushing force of 500 tons each, and 192 Enerpac cylinders, which have a pushing force of 250 tons each. In order to stabilize the bridge during construction, seven temporary piers have been built between the permanent piers. The temporary piers will also help launch the deck spans.
In 1988, studies by the French Department of Transportation found that a route across the Tarn Valley would greatly ease congestion on the A75 motorway, the link between Paris and Barcelona. In 1989, the idea of a bridge that would soar over the valley was accepted, because it avoided the necessity of a tunnel. Construction of the project began in 2001, and is slated for completion within two years.