- Bridges and footbridges
Viaducts at 'Le Boulonnais'
A16 motorway, France
Bouygues, Norpac and Demathieu & Bard
Architect : Carlier
In order to join Boulogne-sur-Mer most quickly, three viaducts cross the valleys of Quéhen, Hermerangue (Herquelingue) and Echinghen. The characteristic of this work comes from the use of bracons, because their structural role made it possible to thin the profile of the deck, and to reduce the width between the posts. Thus, the general profile of the work is lighter. The lower flagstone of the deck supported by concrete posts is connected to the higher hollow block three times broader by a lattice of steel tubes. Each voussoir is composed of a lower precast beam with 8 bracons that support the 3 elements of the higher hollow block following a triangular provision. For the viaducts of Quéhen and Herquelingue, length 474 m and 260 m respectively, the voussoir has a total height of 5,50 m, whereas this height goes until 8 m for the support of the longest spans (110 m) of the viaduct of Echinghen, 1301 m long.