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New Coastal Road : The next stages of the construction of the viaduct

26 juillet 2016

Though Coastal Viaduct is one of the main large-scale civil engineering works of the New Coastal Road. After the launch of the prefabricated phase of the different elements of the viaduct (piers and voussoirs) in the factories of Le Port, the next stage of the construction is the start of the work at sea. A situational analysis of the construction of the 5.4 km Viaduct, visible at sea.

THE BARGE ‘ZOURITE’ TO START WORK OUT AT SEA TO PLACE THE PIERS

At the end of July, the la barge will carry out tests at sea for positioning and self-elevation manoeuvres of the platform. The next step will be to install the first pier at sea, after loading at the quayside (Port Est) of the first base section in early August to transport it out to sea off Grande Chaloupe. Zourite will then install the top of the pier and of the pier voussoir, the first section of the deck of the viaduct.

Construction out at sea is now visible. The first pier (P48) will have been installed at sea by late August. Construction of the second pier (P47) will take place late September-early October, necessitating just two trips (base section, then top of the pier and pier voussoir). The Coastal Viaduct will have 50 supports, 48 piers out at sea and two supports on the dikes, referred to as ‘abutments’ (one support at the Grande Chaloupe end and the other at the St Denis end).

The crew of the barge is made up of six naval staff (2 officers, 1 boatswain, 1 oiler and 2 sailors) and 15 persons will be working on board to carry out the work at sea, notably the concrete for the joints between the upper and lower sections of the piers.

A dedicated fleet of vessels also accompanies the barge with :

  • 1 pontoon for improving the condition of the sea-bed and laying down the anti-scouring mats. This will be brought in from the NEPTUNE shipyard in Holland ;
  • 1 technical assistance vessel (SSE multicat) for supplies (water, fuel, spare parts etc.) ;
  • 3 vessels for transporting staff (Actamarine) ;
  • The fleet of the sub-contractor SDI (Société de Dragage Internationale : International Dredging Company) :
  • The Pinocchio dredger (hydraulic excavator on pontoon) ;
  • Two separable barges for evacuating materials out at sea (self-powered, 60m in length and with a shaft of 1000 m3)
  • An assistance multicat and a bathymetric launch (for measuring the topography of the sea bed)

AT THE GRANDE CHALOUPE END, THE FIRST SUPPORT (ABUTMENT) FOR THE VIADUCT, BEING CONSTRUCTED ON THE DIKE

In order to link up the Coastal Viaduct to the dike, (D2) to the east of Grande Chaloupe, the abutment (C49), adjacent to the far end of the viaduct, is in the process of being constructed. The concrete for the base was laid down in June and construction of the structure is continuing.

THE TRUCKS WILL START TRANSPORTING THE VOUSSOIRS IN SEPTEMBER AND OCTOBER

To deliver the running voussoirs, which will make up the deck of the Viaduct, the three trucks – 35 m in length, 5 m in width and equipped with 216 wheels (capable of transporting the equivalent of a three storey block of flats) – will begin night deliveries between Port Est and Grande Chaloupe by late September or early October, driving along the existing coastal road, where traffic will be diverted to the mountain side of the road to limit any disturbance caused by these deliveries.

THE BEAM LAUNCHER IS PREPARING TO INSERT THE RUNNING VOUSSOIRS

Up to late July, after mounting at the tip of Port Est and following tests to be carried out in August, the 278 m long and 28 m tall beam launcher, custom-built for the project by CIMOLAI (Italy), will make it possible for the voussoirs to be installed as from October. Once delivered by the trucks, the elements of the deck will placed by the gantry and assembled on either side of the pier voussoirs. The beam launcher will move forward little by little from Grande Chaloupe to Saint-Denis as construction of the viaduct advances

ACCELERATED PRODUCTION OF THE ELEMENTS NEEDED FOR THE VIADUCT IS CONTINUING IN THE FACTORY PRODUCING THE PREFABRICATED SECTIONS

  • Regarding prefabrication of the voussoirs, the two sections of the pier voussoirs, the voussoirs over the abutments, the six sections of the running voussoirs and the casting mould for the end spans (the voussoirs adjoining each abutment), are now in operation.
  • Regarding prefabrication of the piers, production is continuing and the first section of the bridge deck (pier voussoir) is being assembled.

DIAGRAM OF A PIER AND A PIER VOUSSOIR

The design of the piers, prefabricated on land, consists of two sections :

An upper section, referred to as the head of the pier, makes up the upper part of the vault of the pier and the head section (1)

A lower section, referred to as the base, makes up the foundation footing and the joints linking up to the vault of the pier (2)

A pier voussoir is then placed on top of these, corresponding to initial section of the deck of each pier. The pier voussoir is composed, in its centre, of three specifically-designed voussoirs, on either side of which is added of a pair of running voussoirs. This massive part is, therefore, made up of seven voussoirs, and weighs a total of 2 400 tonnes (3).

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