References
Safina Dry Dock - Hydrolift
UNITED ARAB EMIRATES, 2005 - 2006
The Dubai Drydocks naval shipyard has extended its capacities by commissioning a hydrolift for the construction and repair of floating equipment. This structure was entirely completed by Soletanche Bachy acting as the main contractor under a design and build contract.
Design
The launching facility acts as a lift between sea level and the dock water level. It enables the vessel to be moved vertically and horizontally and acts like a slipway but incorporating a reverse hydraulic process.
The structure comprises:
- one transfer platform (70m x 170m), set above sea level;
- a harbour basin (65m x 135m) that opens out to the sea;
- two abutments and a sill between, which support the 65m sea gate;
- one quay platform measuring 27m x 89m, which houses the pumping plant;
- two gates: a seaward caisson type gate and a landward modular gate;
- two mooring dolphins.
The conforming design envisaged sheet pile wall held by ground anchors to form the basin. Solétanche Bachy came up with an alternative solution that replaces the sheet piles with diaphragm walls. The diaphragm wall was mostly cantilever and was constructed with T panels. The wall along the transfer platform was constructed using flat panels.
Construction
300,000m3 of sand was first brought in to make a working platform for the land construction of the diaphragm walls and pile installation. Diaphragm walls were constructed all around the basin and also along the perimeter of the two abutments. A sheet pile cofferdam, connected to cast-in clutches in the diaphragm wall, was constructed between the abutments, to allow the construction of the sill and the abutments in the dry. The sill was founded on barrettes and concrete piles. Dewatering of the sill and abutments was achieved with 10 deep wells. All works were done in the dry. Cast-in couplers were used to connect the diaphragm wall to the abutment structure. Leaving a bund at the sea end allowed the basin excavation in the dry. Dredging to final depth was then carried out inside of the basin. The transfert platform is founded on CFA piles.
Techniques
Regardless of site size, and providing it involves a significant proportion of works in the ground, Soletanche Bachy will handle the complete project, and all aspects of the works, including site supervision, excavations, foundations, civil engineering and all construction operations.
A diaphragm wall is a reinforced concrete wall that is made in situ. The trench is prevented from collapsing during excavation, reinforcing and casting by the use of supporting bentonite slurry. The slurry forms a thick deposit (the cake) on the walls of the trench which balances the inward hydraulic forces and prevents water flow into the trench. A slurry made of polymers can also be used.
A ground anchor is a load transfer system designed to transfer the forces applied to it to a competent stratum. An anchor is said to be temporary if it has a lifespan of under two years and permanent if the lifespan is over two years.
A pile is a structural element driven into the soil for transferring loads and prevent deformation. Its slenderness ratio is not limited.
Pile shafts can be uniform and rectilinear, telescopic and belled out.
Piles can be installed either separately or in groups. They can also form a retaining wall, a mixed curtain wall, contiguous piles, secant piles and composite curtain walls, such as Berlin walls and similar. Piles are also used as precast beams to be placed in the structure of the building they support.
Ouvrages
Voyage au coeur de l'ingénierie de pointe
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