Sea walls: to the nearest centimetre

Less than one centimetre. This is the margin of tolerance established for positioning the more than 80 concrete components that will make up the sea wall. It is a real feat, especially if we know the measurement of the concrete blocks. Weighing 16 tons each, 8.4 metres long and 2.4 metres high, these “monuments” need very special resources. So special that a device has been designed especially for this work, explains Sylvain Bellet, the Civil Engineering Manager of the operation. The first stage is to manufacture the blocks in Marseille. The components are being made to measure following surveys on the positions of the caissons in Monaco. 

By the beginning of December, half of them had been built. The second phase is to transport them to the Principality by land. Once here, each of these blocks is positioned with the help of this unique device, which is equipped with height adjustable legs. Topographical surveys are carried out to adjust the component across all three dimensions within the one centimetre margin of tolerance. 


Once its position has been checked, each block is reinforced and grouted, meaning that it is attached to the works. The entire positioning process is scheduled to to be completed next February. Two ten-member teams have been created for greater efficiency. Positioning will begin towards the middle of the ring of caissons, and each team will work towards the western and eastern extremities of the project, which will enable precious time to be gained. These elements of the sea wall are part of a much larger whole. In effect, they will “dress” the caissons of the ring, which are already in place. But this is only one stage. Subsequently, they too must be capped with a handrail to ensure personal safety all along this future promenade, which will wrap around the periphery of the new district. The sea wall and the handrail will have an additional constraint. Because they are areas that are especially exposed in his regard, they must have a truly flattering visual aspect. The specifications regarding colours and surfacing are therefore very demanding, which multiplies the technical constraints of the operation.