Piling into work on 360m Torch Tower

Despite the volatility of labour and material prices, the contractor building the Torch Tower in Dubai Marina is working to a fixed price. Zoe Naylor reports on the initial stages of construction on this super tower.

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By  Zoe Naylor Published  April 1, 2006

|~|115proj200.gif|~|Piling and work underway in Dubai Marina on what will be one of the tallest residential towers in the world.|~|Dubai has earned the well-deserved moniker of ‘the city of superlatives’ — and the new US $191 million (AED700 million) Torch Tower, which is currently under construction in Dubai Marina, is no exception. When complete, the 360m-high superstructure will be one of the tallest new residential buildings in the world. And a tower project such as this demands a range of cutting edge construction techniques, especially in the design stages. From the piling and ultra high-strength concrete, right through to a tower crane-mounted web cam to show overseas customers up-to-date progress of construction, the project team is aiming to deliver maximum quality in the minimum amount of time. Dubai Civil Engineering (DCE) is the main contractor on the job, with National Engineering Bureau (NEB) as the design consultant, developing the original architectural concept from Khatib & Alami (K&A). Zublin Ground & Civil Engineering is the contractor for the piling and shoring works. The firm started work on site in February, and is nearing completion of its package. “The secant pile wall is formed using a continuous 90cm diameter pile, incorporating an ‘over-cutting’ technique. This pile wall includes a three-layer anchor system to withstand the earth and water pressures,” says Holgar Wolfle, the project manager for Zublin. The main structure foundation piles are driven into the ground to a depth of 50m and have been re-designed to incorporate larger diameter piles under the central core spine, where the greatest pressure exists, to increase the stability of the structure. According to Wolfle, on three sides of the site the shoring system is already finished with only the anchor layer still to be installed. The remaining side, which completes the shoring system, will be formed using a 1.2m-diameter pile that does not require any anchors. “After we’ve finished the shoring works, we will start the excavation and then the dewatering,” adds Wolfe. The rest of the dewatering will go down below the final excavation depth. “We are not lowering the water table outside of the site, only inside.” Main contractors DCE will take over as soon as Zublin finishes the piling. “We’re looking to come in around August or September 2006,” says Venu Menon, project director, DCE. “We will start off by cutting the piles and doing the excavation for the four basement floors,” he adds. The tower will comprise four basements plus a further four floors above the ground — a total of eight floors for car parking. Above these will be the leisure deck, with the residential area beginning on floor six. There also will be access to the roof to allow residents a panoramic view of the skyline. “The four basement floors, the parking floors and the leisure deck will each take up an area of around 3400m2 per floor. Once we start the residential units, this will decrease to around 1100m2 per floor,” says Menon. The building will then be brought up gradually using slip form formwork, provided by DCE, to cast the floors. “DCE has an in-house slip form division which will be slipping the core,” explains Menon, “and we will always be three to four floors ahead of the slab.” The concrete for the floor slab will be 4m thick. All the slabs will be post-tensioned, again by DCE — the company was in fact one of the first to bring post-tensioning to the UAE market. “We’ve done around 150 towers in Dubai and Sharjah — in Dubai Marina last year we handled over eight towers, and we currently have another seven in various stages of completion,” says Menon. He says that all DCE jobs use post-tensioned flat slabs. “This has the definite advantage of not having any drop beams, which makes life easier for the mechanical services, and speeds up the job.” One of the most striking features of the tower (and the one that gives it its name) is the large LED display, which will be installed at the top of the building. The fully programmable iconic screen is likely to measure 30 to 40m in length, with the display being formed into a flame-shaped poly-carbon structure at the top of the tower. “This could be used as an artistic decoration feature, which could be displayed on the screen,” explains David Mullen, project manager at Dubai Select (the project’s developer). A building of this height demands very high-strength concrete. “Tall structures will have a certain degree of movement nearing the top and it is normal to expect lateral sway of around 30cm in structures of this height. “In the floor sections we will be using 60-Newton concrete, and in some of the lower columns, 100 Newtons; but typically the building will be around 80 Newtons,” says Mullen. Cladding on the building will be a mixture of aluminium and glass and will be provided by DCE. “The lead time now for glass is about 12 weeks,” says Menon. “We have a licence to use an American profile and we buy the glass locally. “But aluminium is no problem since we have our own extrusion factory in Dubai Investments Park,” he adds. “There are very few things we don’t do in-house, but one is readymix,” admits Menon. “We buy this from firms such as RMC and Unimix.” He says that tower projects demand one readymix supplier right from the beginning: “After eight or 10 floors you need to have a hydraulic placing boom and a stationary pump. And the supplier of this boom and pump won’t allow any other supplier to pump concrete through their equipment.” Despite the plot’s location slap bang in the heart of Dubai Marina, Menon says that he is not anticipating any problems with delivery of materials: “Three sides of this site are surrounded by an asphalted road. And once the parking floors are built, we’ll use them as a storage area for all the finishing materials to help maximise space.” In a bold manouevre, Dubai Select pre-agreed a contract price — around US $191 million (AED700 million) — with DCE at the start of the project. “We’ve guaranteed a maximum price we’re going to pay DCE, and we believe we’re the first to do that in the UAE,” says Mullen. But what happens if the price of steel, for example, shoots up again? Not a problem, according to Menon: “We have arrangements in place if there are substantial price increases,” he says. “Rebar is a potential problem, as we used to source it from a factory, but now we’ve set up our own facility in Jebel Ali, which will go into production in a month’s time.” While DCE appears to have most bases covered thanks to its sizeable in-house capabilities, Dubai Select has decided to add a high-tech touch to the project by making use of web cam technology to show its Torch Tower customers what stage construction is at. “Around 80% of the tower has already been sold, mainly to customers in the UK, so we decided to install a web cam on site, so people can access the project wherever they may be,” explains Mullen. “It is new for our customers, and as far as we know it’s new for Dubai. We’re going to move the web cam around the site, so people can see the entire construction process,” he adds. The quality of the construction process will come under close scrutiny via a long-term facilities management (FM) programme that has been devised by Dubai Select. “We’re already looking at the maintenance of the block and have devised a 10 to 20-year facilities management programme, which will include checking the post-tensioning for the concrete and looking at the fixing points,” explains Mullen. “We have around 30 contractors in line for the FM contract with bids due back in the next few weeks.” Although the FM award won’t be made until after the first year of maintenance from DCE, Mullen says it’s important to get the procedures in place now. “Look around and you’ll see we’re in a very dynamic market — contractors are over-stretched, and if you don’t get them signed up in advance there may not be any available.” When the building is completed it is likely to be another landmark in the city of Dubai, according to Adnan Rahhal, project manager at NEB. “It’s going to be a unique tower in terms of its shape, height and location,” he says. “There aren’t many towers above the 50-floor mark in this area.” And judging by the fact that Torch Tower is already 80% sold, it would appear that Dubai’s construction flame is in little danger of blowing out just yet.||**||

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