The areas dedicated to leisure activities are estimated at50,000m2 office space at 100,000m2 while accomodation will be in the order of 200,000m2 The garden areas will be 40,000m2 while the new marina created between the dike and the tower will represent some 70,300m2.
THE TOWER'S STRUCTURE
The overall structure will be in two parts: the superstructure which is the Tower itself and the sub sea structure composed of the three caissons.
The caissons are the structural link between the cretaceousseabed and the tower. From sea level to +66 in, the Tower willbe pre-stressed reinforced concrete structure. Above +66 m,and up to +390 m, the Tower will be a steel structure in orderto reduce the total weight (Fig. 6).
Fig. 6
THE CAISSONS
The concept is partially derived form the North Sea Ekofisk Central Complex outer wall and other offshore concrete structures. A watertight double wall ring is built firstly in a dry dock and later in a floating mode using the conventional ”slip forming” method. The ring caisson is surface-towed to its final location and sunk in place. A seal will enable emptying the inner volume of the caisson, thus providing a dry.
The construction steps are briefly described as follows:
Step 1: At a dry dock the base of a double wall ring, some 100m in diameter, is built to an elevation sufficient to provide a positive buoyancy. The base of the watertight structure is designed with a sealing system for future installation purpose. The double wall structure provides the necessary buoyancy, strength and stiffness for the caisson.
Step 2: The dock site is flooded and the ring caisson towed to a protected location (deep harbour or bay) with sufficient water depth for the structure final draft.
The caisson is built by the "slip forming" method to it sultimate height, that is several meters above sea level when in place. The double wall, strengthened by a cellular struc- ture, is flooded step by step to ensure the caisson stability and to facilitate the construction work. This is commonly done for example in the Norwegian fjords.
Step 3 :The seabed at the site offshore Fontvieille is prepared, for example by dredging, in order to remove unconsolidated materials and to provide a solid and levelled base to receive each caisson.
Each caisson is surface-towed from the construction yard to its final location and sunk accurately in place by additional controlled flooding of the double wall cells. Offshore positioning allows today an accuracy in the order of ±1 meterer even better.
