The teams on deck

Publication date: October 2, 2019

The T12 tram line will cross the A6 at Grigny, Ris-Orangis and Évry-Courcouronnes. The construction of these three bridges is a major project. Giuseppe Infante, project manager at Île-de-France Mobilités, explains the details.

What will the bridges look like?
On each bridge, the tramway will run in both directions: on those of Grigny and Évry-Courcouronnes, pedestrians and cyclists will have a dedicated lane, while in Ris-Orangis they will use an existing underpass. The bridges will be between 60 and 95 metres long. Because of their proximity – they will be 2 kilometres from each other – it was important to create visual homogeneity for motorists who will see them from the A6. Their design will therefore favor lightness. The right angles have been set aside in favour of rounding. However, they will be imposing structures, the heaviest bridge will weigh 1,300 tons! The box will be made of metal and the top slab of concrete. Thanks to the Corten steel, ochre shades will give a very beautiful patinated effect. This steel also has benefits in terms of maintenance. Requiring no paint and rust resistant, there is no maintenance to be expected.

How are they constructed?
After the studies carried out by the specialized engineers, the metalworkers cut the sheets and prefigure the caissons. Then the welders and metal carpenters proceed with the assembly, on one of the two sides of the bridge. Nine months later, the booksellers are ready to build bridges. At each stage, we must comply with drastic security measures.

What is "launching a bridge"?
It involves pulling the bridge using a cable attached to the back of the bridge and operated by a device called a "winch". No towing machine intervened. Once the bridge is pulled, it is lowered to its operating height. It is a very advanced method, which requires preparation and precision to the millimetre.

What is the timetable for this operation?
The Grigny and Ris-Orangis bridges were launched in September 2019, and the Évry-Courcouronnes bridge in the spring of 2020. During this operation, traffic on the A6 is interrupted at night for five weeks, while the launch is being carried out, the installation on its final supports and the finishing of the installation. Diversions have been and will be offered to motorists on the A6 via the A10, N104 and N7.* Many players (technical teams, operating agents, etc.) are mobilised for the launch. Coordinating such a project is as complex as it is exciting.

*These closures are announced on the project's website and Facebook page.