The Grande Ravine Viaduct

VINCI Construction Grands Projets was approached by Reunion Island for the construction of the Grande Ravine viaduct. This viaduct is one of the four exceptional bridges built on the hillside along Route des Tamarins (dual carriageway on the west coast). This new 32-km road connects Saint-Paul with Étang-Salé to relieve the completely saturated RN1 national road. To be more specific, our contract was to construct a 288-m-long and 20-m-wide viaduct spanning the 300-m-wide and 170-m-deep Grande Ravine in the middle of Route des Tamarins. The project was launched in 2006 and completed in 2009.


RN1 (a dual-lane road linking Saint-Paul to Étang-Salé on the west coast) is nestled between the sea and dizzying cliffs and reaches a height of 100 metres in certain spots. It was not only the island’s most picturesque road but also its busiest. This national road had been congested for years due to growing traffic. The situation led the authorities to embark on the construction of a new dual carriageway parallel to this road, called Route des Tamarins. Built on the hillside, this new road crosses many ravines (gorges with steep sides). So, this road has many outstanding bridges, but the most exceptional, particularly where the technique used is concerned, is our project: the Grande Ravine viaduct, which without intermediate supporting structures is designed to withstand strong environmental, geotechnical and climatic (cyclones) loads. It was inaugurated on May 6, 2009.


The architectural and technical choice of this structure was dictated as much by the nature of the terrain (very steep slopes making piers in the ravine impossible) as by environmental reasons (protected flora and fauna). These constraints led us to design something out of the ordinary. The design was oriented towards a light and uncluttered deck, like a fine blade, supported by two arms coming out of the sides of the ravine: the braces. A steel deck and orthotropic slab viaduct with two high-performance prestressed concrete braces at an angle of 20° was designed. The deck is entirely in steel with a constant height of 4 metres, width of 20 metres and length of 288 metres. It is supported by pivoted braces and sliding bearings on the abutments. Consequently, a large part of the forces acting on the deck are transferred by the prestressed concrete to the massive abutments, which makes it a special bridge with a limited and controlled load effect on the arch.
The deck was installed by launching from the two sides of the ravine. Successive overhang construction was used for the braces, which were held up by temporary straps when the deck was launched halfway from each side. They were then inserted full length into the buried counterweight abutments and held up by straps made from prestressing cables running inside the deck. Each abutment was set on a superficial foundation footing behind the counterweight and on a foundation pit in front.
Finally, the work was also subject to climatic constraints: it was tested to resist cyclones up to a maximum speed of 270 km/hr. To study the effects of the wind, bridge models were used for wind tunnel testing. This is why the deck is equipped with anemometers and accelerometers for real-life monitoring of the structure’s behaviour in the wind.

The presence of protected bird species on the site, such as the tropical shearwater or Barau’s petrel, precluded any cable-stayed or suspension bridge option.


By virtue of its exceptional environment and unique design, the Grande Ravine viaduct posed a permanent technical challenge from the start of the design planning until the end of the construction. It called for a great variety of construction techniques.
With a length of 288 metres, it is a technical feat because it links two rocky outcrops at a very high altitude to cross the chasm of the Grande Ravine, which has impressive dimensions – almost 300 metres wide and 170 metres deep.
To build this structure, the group made use of the most advanced engineering techniques: high altitude supports, deep foundations, interior and exterior prestressing, high-performance concrete, successive overhang brace construction, metal deck with high elastic limit steel assembled and installed by launching and the monitoring of sensitive construction stages using electronic deformation and pressure sensors.
Beyond these architectural and technical feats, this viaduct was part of a larger plan to decongest traffic on Reunion Island and create a new road linking Saint-Paul to Étang-Salé.

Project management

Région Réunion

Project management
Setec TPI

Key figures

Implementation dates
April 2006 to June 2009  

12,830 m3

14,130 m3

Prestressing steel
57,560 kg


“The site is at a height of 250 metres and affords a clear view of the ocean. It’s a place in the wilderness that is difficult to access. The site had to be supplied with electricity from a power generator and water in tanks and containers.”


New coastal road

Saint-Denis-La Grande Chaloupe