Piling into the gaping hole at Dubai Festival City starts

The excavation works and dewatering for Zone 8, the retail component of Dubai Festival City, are now complete. Piling is underway and work on the superstructure is expected to start in the next few months. Construction Week visited the site to see how this part of the development has progressed so far.

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By  Colin Foreman Published  April 25, 2004

Piling into the gaping hole at Dubai Festival City starts|~|DFC body.jpg|~|Piling work, with Swiss Boring as the contractor, began earlier this month. |~|A gaping hole currently dominates the Dubai Festival City landscape. The excavation and dewatering are the first works to be completed on Zone 8, which when complete will be the ‘crown jewel’ of the entire 1600 acre development. The design of the waterfront entertainment and retail centre draws inspiration from around the world and will be a leading two-level, enclosed, retail environment providing 110 000 m2 of gross leasable area for the client. The zone also includes an active marina, a promenade and canals with water transport. In total some 830 000 m3 of material has been excavated to create a 4-5 m deep chasm that covers an area of some 160 000 m2 alongside the Creek. “Of this material 260 000 m3 was stockpiled for use elsewhere on site, as retaining walls for example, and 570 000 m3 of material has been carted away,” says Michael Beggs, project manager, Dubai Festival City. Aside from the extensive excavation work Al Futtaim Carillion was also required to dewater of Zone 8 site to give a stable platform for the subsequent piling work. With the excavation site being so close to the Creek the groundwater level was directly related to its 1.5 m tidal range and stood at +0.7 m. This has now been stabilised at the –4.5-5 m level to accommodate for piling works and a construction platform of –2.5 m. When complete, the retail centre’s double-decker basement car parking will be 2 m deep. For the dewatering a drain and sump pump system was used together with a series of drains running around the perimeter and across the site. These trenches were then walled with stone and geo fabric and sloped down towards the sump pumps that pumped the water into settlement tanks. In these tanks any fine sand that has been collected by the groundwater is “settled out” so that just clean water is returned to the Creek. This pumping is a continual process. If it stopped the water table would return and the groundwater level would return to its previous level. “Pumping will continue until the substructure works have been completed, the ground water can then come back up again, but that doesn’t matter because the substructure will already be built,” says Beggs. water tight When the substructure works are complete it will be sufficiently stable and water tight so that the building will not be affected by the groundwater. Keeping the substructure stable will be a piled foundation consisting of some 2918 piles. Certain piles will be tension piles and hold the structure down to prevent it from floating away. This is of particular importance because a marina will be created that will run alongside the retail centre. “At this stage the marina has not yet broken through into the Creek, but once the marina wall is built the existing material will be dredged out forming the marina. Two-thirds of the marina is currently dry land,” says Beggs. “When the marina is complete, the groundwater levels around the retail centre will be greatly affected by the tide,” he adds. Al Futtaim Carillion will remain responsible for the maintenance of the dewatering until the contractor for the substructure arrives onsite later this year. The dewatering was part of the package that was put out to tender so they now they have to maintain that dewatering until the piling is complete. When tendering the substructure, the contract will include the take over the dewatering until the substructure is complete. “The decision was made that because the excavation contractor had to dewater to excavate it made sense for him to dewater as well. There was some talk in the planning stages of giving the piling contractor the task of dewatering but it was felt that it would be a smoother process if the excavation contractor dewatered until the substructure contractor started on site. Dewatering is not normally a piling contractor’s forte, so it also allowed them to focus on the piling and not have to worry about other issues,” says Beggs. Swissboring were awarded the contract for the piling works on 30th March. Working to a 24 h programme, the contractor aims to complete piling work by 11th August. The piling work involves a combination of pile sizes for different purposes. There are 990 tension piles that are 600 mm to anchor the structure to the site and prevent any uplift from the water pressure. This will vary at different times of the day depending on the tide. The rest are compression piles to support the weight of the structure to be built above. Of these piles 1300 will be 1200 mm piles and 625 will be 900 mm piles. The average pile depth for all the piles is about 22 m. “There are some big piles going in,” says Beggs. resting on grid Part of the reason for this is that the building will rest on an 18 m by 9 m grid so that the parking area can be more open. In other shopping centres a regular 9 m by 9 m grid is normally used. The larger grid means that the load supported by the piles is greater, requiring larger piles. The 1200 mm piles will support a load of 17 000 kN. The 900 mm piles will also support much of the building load in areas where piles can be more closely concentrated, such as lift pits and stairwells. “It has been quite a challenge for the design team,” says Beggs. Once fully complete the building above will effectively be a five-storey building with two basement levels of parking, a ground floor, a first floor, and in some areas will have a second floor. The double-decker basement will provide parking for 6000 cars and will be at -2 m. Zone 8 is just one of Dubai Festival City’s 15 components. Other components include a golf course, an automotive centre and various residential, office, and commercial spaces. The Al Badia Golf Course is expected to be complete this year. Zone 8 will be fully complete in 2006. The target date for the development is 2013.||**||

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