Major milestone in land extension project

The final caisson forming a protection belt for Monaco’s new land extension has been laid, marking a significant milestone in the multi-billion euro project. Next step: backfilling the area with sea sand extracted from the north of Sicily to create an embankment that will reach up to 45 metres high.

The final caisson has been installed on the protective belt of Monaco’s land extension. Photo courtesy Bouygues TP

It took one year for the group Bouygues TP to install all 17 caissons, eventually forming a complete belt of 500 metres around the future extension at sea. The caissons were made in the port of Marseille and towed 200 kilometres by sea to Monaco, where the final one was positioned on 18th July, effectively closing the belt.

“We only had 28cm of leeway on each side to install this final box of a specific, trapezoidal shape,” said Christophe Hirsinger, head of Bouygues TP. “Considering maritime resources were usable only on the sea side, the installation went perfectly.”

One caisson remains to be installed, at the entrance to the land extension, but the completion of the protective belt will allow this development to move to a new stage: backfilling the land-full. It will be carried out using 450,000 cubic metres of sea sand extracted off the coast of Sicily and dumped by a dredge to create, eventually, an area 60,000 metres squared.

At the same time, seawater present in the enclosure will be pumped out and rock armor will be installed to protect the embankment and caissons.

Rendering of luxury apartments on the new Portier man-made island in Monaco. Picture: BOUYGUES CONSTRUCTION

The land intended to accommodate the future eco-district is due to be delivered at the end of 2020, early 2021. The next stage will involve the long process of soil treatment, including vibro-compaction, ballasted columns, solid injections and the installation of piles. In the end the embankment will reach up to 45 metres in height, thanks to nearly three million tons of materials that will have been used to build it.

Before work on the buildings can begin, the infrastructure must be completed, including roads and a storm basin under the Portier roundabout.

“Currently, the number of people engaged in this work at sea has been significant. There are 300 people in Monaco, mobilised on a single post, six days out of seven,” said Mr Hirsinger. “It will take Bouygues TP and its subcontractors four years to complete this new maritime infrastructure from the studies phase and the completion of the caisson belt.”

Monaco’s land extension is serving as a reference in the field of maritime development across the globe, in terms of resources committed, measures taken to control and limit the damage to the environment, and the techniques that have been developed purely for this purpose. The group that manufactured the caissons, Marco Polo, was actually developed in the Baltic Sea specifically for this project, before being transferred to the port of Marseille. It will now be used for other projects in Europe.