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Neighbourhood on the water: a titanic construction project

Presented as the eco-district of the 21st century, the Monaco sea extension will stretch from the Grimaldi Forum to the Fairmont hotel in 2025 and will involve a very carefully organised project for its construction. The project has arrived at a crossroads, between the end of the preparatory phase of the site and the start of infrastructure works in April.

This time, Monaco has taken the plunge. Or, rather the stretch, across the sea. Judged too dangerous for the Larvotto marine reserve, an initial extension project of 15 hectares had come to a standstill in 2008. Five years later, Prince Albert gave new life to a project of 6 hectares and construction company Bouygues swept the market in January 2014. These days, the ambitious project has been coming to the heart of the matter. At the beginning of April, after months of fine-tuning the smallest details for an eco-responsible project, the preparatory phase will make way for the first infrastructure works at sea. Then, in 2020, a new neighbourhood will emerge from an artificial piece of land at a titanic price. Delivery is scheduled in 2025. On the programme: 120 luxurious dwellings, 3,000 shops or a harbour with about thirty moorings. A complete neighbourhood delivered in one go and directly connected to Grimaldi Forum, destined to grow also. The area will have plenty of fresh air too, thanks to new footbridges.

In total, it represents two billion euros of private investment, half of which solely for maritime infrastructure, entirely borne by the Société Anonyme Monegasque (SAM) Anse du Portier. It is a grouping of Bouygues Travaux Publics, local companies such as JB Pastor & Fils and Engeco, and “a number of investors who do not wish to be named,” according to SAM Anse du Portier, Régis Adeline. “Investors who know Monaco well,” reassured the director of the Urbanisation at Sea (Urbamer) mission, Jean-Luc Nguyen. The latter praises the size and shape of the extension, designed to match the a typical Monegasque current. “The abandoned project was larger and therefore would have gone down to a depth of 70 metres (against 50 today) and the extension could have obstructed the marine current. With this project, the coastal current is hardly impacted.”

sea extension

“A showcase of dynamism”

Associated with big names, such as the architects Denis Walode and Renzo Piano or landscape architect Michel Desvigne, the project has been called the “eco-district of the 21st century”. “A showcase of the dynamism of Monaco in total harmony with the existing one”. Will it become a model for other places in the world? “It is easier with financial backing that has been in place here, but it could inspire other future projects”, conceded Jean Luc Nguyen. Although the specifications give a high priority to maritime transport, the operation will not be neutral in terms of problems. The work will also be forced to stop during the Formula 1 Grand Prix and the Yacht Show. At the request of the Larvotto merchants, an information meeting was held at the Ministry of State on 2 March. Assisted by representatives of the Monegasque Association of Professionals of State Tenants, they expressed some fears about “the impact that such a site could have on the attractiveness of the only seaside resort of Monaco”. All parties were reassured by the strident standards of water quality control, and by innovative devices to reduce disturbance. The merchants also greeted the outstretched hand of Jean Castellini, adviser of the government Ministry of Finance and Economy, for whom “it was difficult to judge precisely the commercial impact of this project. There may be a decrease in activity or presence. The government, through the Domain Administration, is willing to discuss it later and “individually”.

Eventually, the size of the Principality will increase by six hectares. That is 3% of area gained. Enough to put everyone in agreement.

The major stages of the construction project

“So far everything has gone as planned,” Regis Adeline said. Starting last year, the site’s preparatory work, focusing on the environmental aspect will be completed by the end of the month. “In comparison to this maritime preparatory work, I think we are really at the forefront of what is being done,” added Jean-Luc Nguyen. A series of pipes will go underground before a large single slab is installed, destined to hold up the future eco-neighbourhood. Finally, the installation of an anti-noise wall to mitigate the disturbance of the local residents, which, once closed, will mark the changeover to the phase of work proper.


To erect 6 hectares of living space on the sea, they will have to work up to 50 metres deep and accommodate a currently irregular drop. In this case, there will be a more pronounced slope on the Fairmont side than on the Grimaldi Forum side. During the levelling, then the fill phase, the worst enemy of the site managers will be the water cloudiness. All these particles suspended in seawater could be potentially harmful if they spread in the Mediterranean. In addition to upstream stream modelling, drastic water quality controls will also be carried out to ensure safe swimming on the Larvotto beaches this summer.

-From April to May 2017: removal of rock fill. The first ships and gear have been arriving in Larvotto Bay at the end of March to “prepare the ground”. Then there will be the reinforcement of an impressive excavator, with a pontoon of about thirty metres, which will load the current rock fill onto barges. Only part of the rock fill at the foot of the dam will be removed. Many stones will then be transported to an Italian port for repackaging.

-May to September 2017: removal of all sediment. The sediments in the water covering the future extension will be extracted in two parts. The first step will be to remove the “pockets of mud sediment, in depth, which present a little pollution”. “Bouygues will remove them with all necessary precautions thanks to watertight buckets. They will then be sent to a reprocessing centre in Toulon,” Regis Adeline explained. Further analysis will assess the remaining quantity at the bottom. The second stage will include a dive to the bottom of the water with “a sort of giant vacuum cleaner” with filters. The suction dredge is supposed to leave the ground untouched.

-From September 2017 to the beginning of 2018: fill stage. With the water and depth overhaul complete, the construction of the embankment can begin. The centre-piece of the operation will happen as early as September 2017. A 200-metre boatfull of filler will work non-stop during the day. The large bits of gravel, from 2 to 18 centimetres in diameter, will be dumped under water. These operations, carried out using a diving header, will not be visible from the mainland.


The key numbers:

  • 2870 000 tons of quarrying material (chippings) will be brought by ship to make embankments supporting the caissons (or underwater chambers), the ballasting of the caissons and the embankments at the rear of the caissons.
  • 1540 000 m3 of embankments treated with marine or terrestrial vibro-compaction.
  • 620,000 m3 of devastated and dredged sediments in place.
  • 110,000 tons of rock fill deposited on the existing Portier dyke.
  • 48,000 tons of armourstone laid to protect the new underwater embankment.
  • 6:00 am to 10:00 pm time frame during which the construction site will be at work–with certain exemptions until one o’clock in the morning.

-From April 2018 to February 2019: creation of the “belt” of the project

Above this compacted embankment will be deposited a hydraulic embankment, 600,000 m3 of dredging sand from northern Sicily. 18 caissons of 86,000 m3 of reinforced concrete, prefabricated in the port of Marseilles and then towed to Monaco, will then be meticulously placed in the water to form the belt of the project.

-February 2019 to the end of 2020: concreting operations

With the project belt erected, activity on the site will accelerate. An internal embankment will precede the finishing of the caissons by concreting and a deposit of vibro-compacted sand. There will be two types of junctions: One on the Fairmont side for the small entertainment port, and the second, on the Larvotto side, where it will be necessary to remove the rest of the rock fill “to achieve a proper connection between the extension and the current coastline.”

By the end of 2020, the maritime infrastructure will be completed. “After that, it will be a big, but traditional building operation.”


Operations subject to permanent checks

From April 2017 until the completion of the maritime infrastructure works in 2020, operators of the extension project will have a main obsession: turbidity or water cloudiness. That is to say, the content of light materials (mainly sediments) in seawater. It is a strong indicator of the smooth operation and the (quasi) neutrality of their impact on the local ecosystem. Thus they have conducted many preliminary studies and established repositories, safeguards. Sensors were placed in the Roquebrune-Cap-Martin reserve. Similar to that of Monaco, it will serve as a standard for detecting any outbreak of sediment and other potential pollutants. “Measurements are made continuously by an automatic recording device and sent on a website to which Urbamer, the companies and I have access in real time. This access is completely transparent and we know how to check it in real time,” assured Régis Adeline. As a preventive measure, an anti-turbidity screen of 300 linear metres by five metres will also be deployed in the vicinity of the intervention zones. Its aim is to prevent the sediments and other pollutants carried to the bottom of the waters from spreading in the marine reserve and jeopardising the fauna and flora.

Movement of seagrass, mother-of-pearl

Before working on the site, it has been necessary to preserve the marine environment and to limit the impact on the Larvotto neighbourhood.

It began under the sea. Before the start of the project, the preparatory work was placed under the sign of the protection of the environment. Work is due to be completed in early April, before construction begins. This preparatory work has included the relocation of certain protected species: mother-of-pearl, seagrass… after extensive inventory work was carried out upstream.

-Divers have moved 135 large mother-of-pearls. They have been moved from the Mediterranean to the Larvotto reserve.

-Posidonia seagrass beds to be displaced with a new method.The test phases started in January thanks to the “watertracks” technique which will be the subject of a “scientific research protocol”, continues Régis Adeline. The seagrass bed will be followed over a decade.

-Eight blocks of rocks change location. Blocks of rocks with gray seaweed are leaving the Portier area. In all, eight blocks will be moved to the foot of the Oceanographic Museum of Monaco.

-Work to eradicate Caulerpataxifolia has been carried out. This killer seaweed, sometimes dubbed the “green plague”, has lost much ground in recent years.


Jean de Vaugelas, marine biology researcher at the University of Nice, has supervised the transplanting of the large mother-of-pearls in the Larvotto reserve in November and December last. He has been working on the Larvotto reserve for a decade, and has tested a new method of transplantation. Follow-up of these mother-of-pearls must be carried out over five years.

What is at stake, in the protection of mother-of-pearl? According to de Vaugelas, “They live for a long time, up to thirty years. It is very rare among marine animals. It is very interesting to follow them over time, as an indicator of the quality of the environment. This animal is a filter: everything that passes in the water, they recover it. They are indicators for pollution problems.”

From these details, it’s clear that the Monaco sea extension has been carefully thought through in every stage of the project’s construction, to both protect the environment and dazzle future residents and shoppers.

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