A project with multiple challenges.
To become a European-level stadium, the Vélodrome had to start by increasing its capacity. This was therefore extended to 67,000 seats (from 60,000 previously) including 25,000 new seats. Six thousand premium seats and the associated hospitality facilities were also created. In parallel, parking facilities had to be extended with an additional 3,000 sqm of infrastructure, and a secure access route was created for “away fans” for their visit to the stadium.
Long design studies for the roof
Located merely 2 km from the sea, the Vélodrome is highly exposed to the wind. While covering the stands for the convenience of spectators appears an obvious choice, it proved to be a tricky challenge for our teams at Elioth (Egis group), who specialise in building structures and facades.
Studies were conducted by the CSTB (the French scientific and technical research centre for buildings) to adapt the structure appropriately to climate conditions. Tests were consequently performed on various mock-ups in the atmospheric wind tunnel at CSTB’s Nantes offices. These tests helped ascertain the effects of the wind on the roof, which thus allowed our experts to design the best possible roof.
Our ultimate choice was for a Teflon-coated fibre glass membrane, fitted to a metallic framework weighing nearly 6,000 tons. To hold it up, four struts were installed inside the ground between the existing stands. Its elongated form reduced the weight of the structure.
A new challenge arose during construction phase. Since OM continued to play its home games at the Stade Vélodrome, work had to be interrupted every match day. Our teams therefore ensured that the work underway did not impact spectator comfort or safety.
Coping with environmental hazards
As well as the wind and the rain, other climate criteria also had to be taken into account by the design studies.
To ensure that the grass could continue to grow sufficiently without the use of artificial light, we carried out a study on the pitch’s sunlight exposure to assess the minimal surface area of transparent roof. Finally, thanks to the discharge from the neighbouring wastewater treatment plant, we successfully created a district heating loop to generate the energy needed for the operation of the stadium, whatever the season.