Major port development project in Brest
Many ports in Europe are investing in infrastructure to accommodate the rapidly developing renewable energy industry. A good example of this is the port of Brest in Brittany, France. In 2007, Région Bretagne became the owner of the port as part of a reform of French seaports. The port has recently had construction work carried out as part of a €220 million investment programme to maintain its competitive position and create a dedicated area for the marine-related renewable energy industry.
The creation of this new area involves major construction work on land as well as in the water. In 2017, Région Bretagne awarded two important marine contracts – one for reclamation works and the construction of a quay wall, and another for the construction of a breakwater.
The first contract was awarded to a joint venture consisting of the following organisations:
- DEME’s French subsidiary, SDI
- VINCI Construction Maritime et Fluvial (VCMF, formerly known as EMCC)
- VINCI Construction Terrassement (VCT)
- Ménard Agence Ouest
- IDRA Environnement
- GTM Ouest.
EMCC (Entreprises Morillon Corvol Courbot) was a subsidiary of the group VINCI Construction France. In July 2017 it merged with other related subsidiaries such as Tournaud, and now operates under the name VCMF.
The second contract, for the construction of the breakwater, was also awarded to a joint venture consisting of the following groups:
- Bouygues Travaux Publics
- Pigeon Bretagne Sud
- Liziard Travaux Publics
- STPA Travaux Publics.
The quay wall comprises two berths with a total length of 384 metres. The wall itself has a width of 20 metres, but behind it is a 100-metres-wide platform, creating an area of 384m x 120m, designed for heavy loads. The foundation consists of a four-metres-thick layer of gravel, representing a volume of almost 200,000m³.The gravel was dredged at a franchise of Granulats de Manche Orientale (GMO), north-east of Cherbourg. To dredge the gravel and transport it to the construction site in Brest, SDI used DEME’s 13,700m³ trailing suction hopper dredger (TSHD), LANGE WAPPER. The distance from the GMO franchise to the port of Brest is about 265 nautical miles, which represents a sailing time of almost a whole day.
As a result, the LANGE WAPPER delivered its load of gravel (with a payload up to 19,000 tonnes) every two days. The arrival in the port had to be carefully planned in view of the tide. Brest has a tidal range that mostly varies between four and six metres and only at high tide is it possible for a fully loaded dredger to reach the project site. In order to accurately apply the gravel, SDI has purposely built a spray pontoon mainly consisting of modular pontoon sections, a frame, a pipe and a spray boom. At the project site, the LANGE WAPPER could connect to a floating pipeline, which was connected to the spray pontoon at the other end. In this way, almost 200,000 m³ of gravel was successfully applied up until the beginning of August 2017.
Monitoring the environmental impact
During this operation, the turbidity was a special concern due to the presence of sensitive marine species including shells, sea grass and algae, such as Zostera and Maerl. Throughout the entire process of gravel placement, the turbidity was constantly monitored. These values, determined by optical devices, were confirmed by sampling.
In the meantime, preparations were made by the other partners of the joint venture to start the construction of the quay wall. This consisted of two rows of sheet pile wall of the combi-wall type, ie a combination of tubular piles and sheet piles. The quay wall and the adjacent platform are scheduled to be completed by June 2019.
Another major marine contract comprises the filling of the area enclosed by the quay wall and the breakwater with dredged material. Some 1.25 million m³ of dredged material will be used in this reclamation. A total of 550,000m³ will be dredged from the access channel to the new terminal and 700,000m³ from access channels to existing terminals in the port. Due to environmental conditions, this operation has been divided over two dredging campaigns (winter 2018/2019 and winter 2019/2020). Dredging in the port of Brest has to be restricted to the winter months due to the presence in the sediment of the toxic substance Alexandrium minutum, an organism that can lead to paralytic shellfish poisoning. Enclosed in the sediment it is inactive and poses no risks; however it can bloom when released by dredging and activated by the summer sunlight.
Once completed, the new terminal will serve many initiatives related to renewable energy along the French coast, such as floating wind farms on the southern coast of Brittany.
