Le Mont Saint-Michel, France, 2014
Le Mont Saint-Michel, France
Dietmar Feichtinger Architectes
Trophées Eiffel d'architecture acier 2015, catégorie FRANCHIR, lauréat; Équerre d'argent 2015, catégorie Ouvrages d’art, lauréat; Prix National de la Construction Bois 2015, catégorie Bâtiments et Aménagements Divers, 1er Prix
Syndicat mixte pour le rétablissement du caractère maritime du Mont Saint-Michel
EIFFAGE Travaux Public, Eiffage CONSTRUCTION METALLIQUE, Spie fondation
conceptual design, construction design, site supervision (in cooperation with Dietmar Feichtinger Architectes, Paris)
The bridge connects the World Heritage Island and the main land facilitating the movement of residents and visitors to the castle and its surroundings whilst preserving the maritime environment and wildlife. The curvature of the design further provides different viewpoints as the island is approached offering changing perspectives for appreciation.
With a total of 2 km in length, the bridge and the causeway offer road and footpath access; the bridge has a downward gradient of 1% towards the landing platform at the island and at times, the bridge is completely flooded allowing Mont Saint-Michel resumes its island status.
Despite the delicate appearance of the bridge, however, this is a highly engineered site. The maritime site has the highest tides in Europe and shifting sand and sediments are in constant flow, with the bay’s sand floor expected to be 6 to 8 metres lower in the future. The flow of water was therefore central to the design solution, resulting in the construction of 134 slender steel columns with 12 metres longitudinal spacing between them. Furthermore, the precast concrete slabs integrated under the road carry all utility supplies for and from Mont Saint-Michel and cover the bridge.
The requirements for a very strong foundation resulted in concrete piles being firmly anchored on a rock foundation 30 metres below sea level. This design solution allowed the anchoring to occur without the removal of the layers of sand that accumulated over the years on the causeway. The columns were drilled in-situ and the connection between the concrete pile and the columns occurred 7 metres below the current sand levels, a construction method that allows the environmental changes to occur naturally, which was fundamental to preserving the maritime life of the site.
The Bridge was awarded with the French National Award in October 2015 with a spectacular light show. The French National Award is offered to outstanding architectural and engineering design projects, built in France, entirely or partially of steel.