References
Marina bay sands
SINGAPORE, 2007
Basement retaining walls and foundations for 3 high rise hotels
The integrated resort being built on Singapore’s Marina Bay waterfront by Las Vegas Sands forms an integral part of the city state’s ambitious development plan for the Marina Bay area.
The integrated resort will include a casino, a three hotel towers with a total of 2,600 rooms, a 200,000 square feet (19,000m2) arts and sciences museum, a convention centre with 1,200,000 square feet (111,000m2) of floor space, a retail mall and one million square feet (93,000m2) of waterside promenade. casino, un hôtel composé de trois tours, un musée des arts et des sciences, un palais des congrès, une galerie marchande et une promenade maritime de 93,000m2.
The hotel structures, over 50 storeys high, will dominate the Marina Bay skyline. Each structure is different with sloping sides splayed in two directions. The three are linked at roof level by a ‘sky garden’ over 300m long that will offer spectacular views of the vibrant downtown of the city.
Bachy Soletanche Singapore were already on site to carry out the advanced works contract to clear an old seawall mole buried in the reclamation. This contract also formed the cellular retaining walls for Towers One and Two where the abandoned mole encroached on the footprint of the hotels. Known as the doughnut and peanut these were integrated into the final structure as the basement retaining walls.
The contract for the hotel foundations allowed for the construction of the remaining basement retaining walls between towers one and two and for tower three. The foundations for the three towers were essentially barrette piling although there were a number of bored piles for the lighter loaded elements of the structures.
Apart from the buried mole the site offered additional geological challenges due to the nature of the reclamation built over very soft marine clays. The retaining walls and the foundations were required to penetrate into the hard underlying old alluvium with many of the foundations reaching nearly 80m depth.
The Client had set an ambitious programme for the construction of the whole integrated resort and with the three towers being the most complex structures with foundations to match a tight programme was given to complete the works and handover each tower progressively to the follow on substructure contractor.
At the height of the activities on site Bachy Soletanche were operating up to 15 excavating rigs; 3 hydrofraise, 6 KS hydraulic grabs and 6 KL cable grabs all working 24hrs/day, 6 days/week. The logistics to keep this amount of equipment working efficiently meant a strong management team, with a mix of local, regional and European staff. With up to 1,200m3 of concrete being poured per day, at a time when concrete supply across Singapore was extremely stretched, the management of the site logistics was critical to ensure the success of the project.
Given the tight programme, the bored piling and the jet grouting were executed concurrently with the diaphragm walls and barrettes adding to the already complex logistical challenge.
Despite the geological and physical constraints to the works, Bachy Soletanche were able to complete each section of the works on schedule handing each tower over to the follow on contractor to commence the bulk excavation, pile cap and basement structure ahead of the iconic superstructure.
Techniques
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.
Jet grouting is a construction process that uses a high-pressure jet of fluid (generally 20 – 40 MPa) to break up and loosen the soil at depth in a borehole and to mix it with a self-hardening grout to form columns, panels and other structures in the ground. The parameters for the jet-grouting process and the desired final strength of the treated soil depend on a number of characteristics, such as the soil type, the technique used and the objective to be reached. In granular soils, the high-pressure jet breaks up the grains through erosion, while in a cohesive soil, such as clay, the jet breaks the mass up into small particles. High pressure is needed to produce the kinetic energy required for the jet through a small-diameter nozzle. Waste material from the process (a mix of soil, water and binder) is recovered at the surface before being taken away for disposal.
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
Suitable foundations are required for all building and civil engineering structures to ensure that they perform within the settlement criteria established in the design of the structure. Special foundations are used where shallow footings do not provide adequate support for a structure.
Major urban excavations are one of the specialist activities of Soletanche Bachy. Such excavations are required for basements to buildings that are usually part of the foundations of the structure and also used for under-street car parks, cut and cover tunnels for roads, rail, metro and storm water tank...
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