The Jetty – bridge to the Mont Saint-Michel by Dietmar Feichtinger Architectes

December 22, 2015

The jetty is 756m long. It is subdivided in seven sections. The first and final sections are 78m long. Sections 2 to 6 are 120m long. The standard width of the jetty is 12m50. It is composed into a pedestrian part on the west side with a width of 4m50, two carriage lanes 6m50 wide and a 1m50 walkway for pedestrians on the east.

The section rises up to 17m50 (6m50 + 8m50 + 2m50) at the Terminal of the shuttles which is situated 300 meters away from the defense wall of the Mont. The section diminishes towards the Mont and is 10m50 large (4m50+4m+1m50) at the connection with the arriving platform facing the Mont.

The jetty is founded on 67 pairs of concrete pillars 120cm of diameter and 4 more pillars for the abutments. The length of the founding pillars is approximately 30m. The steel piles of the jetty are fixed on top of the pillars about 2m under the estimated ground level after removing the accumulated sand.

Bentonit is used to create the reservation for the pillars. A cage of armature is placed; the piles are precisely adjusted and anchored with concrete.

The pairs of steel piles placed in a distance of 12 m longitudinally are 25 cm of diameter with a thickness of 40 to 60 mm depending on their location. They are also fixed on top to the steel structure of the deck by a welded connection.

The deck is composed of a central part and two side parts as cantilevers. Two longitudinal beams, welded steel boxes are fixed on the top of the piles. They are connected transversally by crossbeam in I section all 3 m. A concrete slab is fixed on the beams for the road part. The top layer consists of a layer of treated asphalt (high pressured water and polishing).

The consoles carrying the side parts are welded on to the longitudinal beams. Longitudinal T-profiles carry the oak planking (50mm of thickness).Expansion joints are provided all 120m.

A continuous bench made of high resistant concrete and carried on double steel plates separates the road from the pedestrian part. LED lamps are integrated under the bench to light up the pedestrian part on the west side. The pedestrian part on the east is lit by floor integrated spots in LED.

The railings are made of steel posts fixed on the consoles carrying a wooden handrail (oak). 9 horizontally stressed stainless steel cables compose the filling. The jetty is the only access road to the Mont Saint Michel. It carries trucks up to 40 tons.

1800 t of steel, 1400 m3 of concrete for the central part with 2 lanes and approximately 4500 m3 of concrete for the foundations. The earthwork for the new dam adds another 45 000 m3.

Anti-corrosive protection for the steel structure is obtained by a coating type C5M for sea environment. The complex is reinforced on the end part towards the Mont where the structure is flooded regularly. The piles standing permanently in the water are treated with a special IM2 coating. Specific elements are additionally galvanized (railing, tubes for conducts).

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