Line 18 viaduct

In December 2020, VINCI Construction Grands Projets (lead) teamed up with Dodin Campenon Bernard, Chantiers Modernes Construction, Freyssinet (all VINCI Construction subsidiaries) and Razel Bec (Fayat Group) to build the viaduct, which forms the first overhead section on Line 18 of the Grand Paris Express.   At 10 metres above the ground, the viaduct deck is in the form of an inverted letter T and shaped like an aircraft wing, giving the structure a lightweight architectural feel. Two launchers (or launching beams) – measuring nearly 100 metres long and 4 metres high and weighing 485 tonnes – were used to lay the segments, one span at a time. Using formwork 10 metres high, the viaduct’s 201 piers were formed with self-compacting concrete (SCC) injected from the bottom of the panels. The advantage of this formulation is that the concrete is highly fluid, filling the formwork more evenly, with no vibration required. SSC therefore helps to reduce arduous efforts for the site teams, while providing an excellent quality finish.

VINCI Construction Grands Projets also selected several options for the construction phase to meet its goal of reducing the carbon footprint of its projects and increasing the sustainability of its structures. These solutions included installing a special mobile production unit at the segment precasting site. This meant that the concrete mixer trucks only had to travel 4 km to the site and back to deliver the mix. 

In partnership with Béton Solutions Mobiles (BSM), formulas could also be co-developed taking a performance-driven approach at VINCI Construction’s test laboratory in Marolles-en-Hurepoix. Mixes were produced containing more than 60% blast-furnace slag for use in the foundations of the piles and almost 60% for construction of the piers.

The formulations used also offer significant resistance to chemical attack. The slag contained in the smooth under-deck also contributed to giving the viaduct its light-coloured appearance, for a sleek, elegant finish, as imagined by architect Thomas Lavigne.

Moreover, 95% of the mixes were produced using recycled water.

Located in the commune of Saclay, opposite the future CEA Saint-Aubin station, the viaduct segment precasting area comprised 10 units and produced an average of 7.5 segments per day. Spanning almost 1.5 hectares, its storage area could hold up to 500 segments, i.e. almost 25% of total production. This area continuously supplied the two launching beams used to assemble the spans of the viaduct.

* Compared with an equivalent traditional concrete solution.