Torch Tower sets record in face of permit delays
After nearly 12 months of waiting for its building permit, a record-breaking concrete pour on Torch Tower's raft has just been completed. Christopher Sell reports from the base of what will be the 10th tallest building in Dubai.
If further evidence is needed of the pace of construction in Dubai, look no further than Torch Tower, which is currently being built in Dubai Marina. Within a period of 12 months, the high-rise, which was originally designed to be the tallest building in the Marina, has now been overtaken in height by 23 Marina, Princess Tower and Marina 101.
The US $118 million (AED432 million) project, which is 352m high, 86 storeys and located adjacent to the Princess Tower and Crown Tower, started piling in February 2006 with German contractor ZÃƒÆ’Ã‚Â¼blin carrying out the works. Dubai Select is the developer, National Engineering Bureau (NEB) is the consultant and Dubai Civil Engineering (DCE) is the main contractor.
David Mullen, development manager, Dubai Select, explains that the project was subject to a lengthy delay as it waited for its building permit before it could proceed. "We applied for the building permit as soon as we received the piling permit, which was back in February 2006, but we did not receive it [the building permit] for almost a year." It was eventually received in December. Mullen believes this delay stems from Dubai Municipality being wary of the multitude of high-rise towers requiring permits and a keenness to avoid any high-profile structural failings.
But Mullen and Elias Fakhoury, project manager, DCE, agree that the system for building permits could do with greater transparency as it currently appears to be 'hit and miss'.
"There are no key performance indicators involved, you just have to hope the plans are acceptable and passed, and that their [DM's] engineers verify the design," says Mullen.
"If you look at it realistically, Dubai is just like anywhere else in the world and it is learning. And DM has to establish that whatever gets built stands the test of time and adds value to the city. I imagine that once all these towers come on-stream, the process will speed up, but at the moment it is a learning curve. If it was England or Hong Kong, getting a building permit would certainly never take a year. A few months maybe," adds Mullen.
"If you look at it on a global scale, everyone is struggling for limited resources. It is the same with DM, there are only so many people who can look at the drawings, know what they are looking at and make the decisions. Training is required to get people up to speed."
This delay has not seen the site stand idle, however, as DCE was able to prepare the site for construction, up to a point, ensuring the piling was in order and mobilisation could begin. This entailed reducing the site down to the cut-off level for the piles.
"Essentially the top two metres of pile is considered no good. Once you have dropped the concrete in and it settles, the top section is not as compact, so it is cut off," says Mullen.
Excavation work on the site was complicated further by a change to the lift pit design. Originally, this was designed to be three metres deep, but it was decided that due to the height of the tower and the subsequent speed of the elevators (6m/s), the lift pit was doubled to six metres in depth.
When Construction Week visited the site, the raft was complete and casting of the basement slabs was taking place. "By this week we will have cast a portion of the second base slab," says Fakhoury.
The project's early construction phase was significant in a number of ways, most notably for achieving the quickest concrete pour in Dubai, for the raft slab. Eleven thousand cubic metres of concrete was poured in just over 28 hours, using 1,375 mixers to dump the concrete using 11 pumps. In comparison, an almost equivalent pour of 12,000m3, took 47 hours on another recent high-rise project in the city.
Not only is the speed of pouring unique, but Torch Tower is also employing super high-strength concrete, which surpasses even the Burj Dubai and the average grade of 50-60N used on conventional buildings.
"We are pouring 90N concrete at the moment, and we will use 100N for some levels. We will be the first in Dubai to use 90N concrete as a slip form - the Burj [Dubai] uses 80," explains Fakhoury. He adds that the benefit of using such high-strength concrete is that it enables the building to use a smaller number of columns, therefore creating a greater floor area. But this concrete does come at a price: "It is at least 20% more expensive," says Fakhoury. Within the raft, 2,600 tonnes of steel was used.
To ensure that the concrete reaches the top of the tower is a further logistical challenge. To overcome this, the project the team will use special stationary pumps, which utilise huge power, together with specially designed pipelines to pump the concrete - which has been designed at a specific thickness to ensure no segregation - to the top of the tower in one go, with no stations in between.
Other logistical challenges focus mainly on hoisting the materials to the top of such a tall tower. "And of course the labourers will be one of the biggest problems. We have 300 now, but this will increase to between 900 and 1,000 when at full capacity," Fakhoury adds. Operating within such a small site presents unique challenges of its own, from keeping it tidy and clear of debris, to storage of key materials used in construction. In this case, the desire to complete the podium stems primarily from the need to use it as a storage platform; a practice that is apparently the norm, according to Wael Hussein, assistant resident engineer, NEB.
For the core DCE will be using a slip form system, which can do one floor height of 3.6m at a time. Post tension slabs will be incorporated with the Doka system. A typical floor cycle is expected to take four to five days.
Operating in Dubai Marina has changed somewhat following the Infinity Tower incident. And while not being directly affected by the newly enforced piling regulations - Dubai Select's other project, Bay Central, has been delayed three months as its piling plans are assessed by a third-party reviewer - since its shoring and piling was already complete, the incident has resulted in a noticeable increase in the number of DM inspectors on building sites. Certainly more so than in previous years.
"I had finished one project, which took me two years, and I maybe saw a DM inspector twice in that time, which was before the Infinity Tower. Now we get four visits a month," says Fakhoury.
The Torch Tower project illustrates not only the physical challenges of building in Dubai Marina, but as an exercise in bureaucracy it demonstrates that like other aspects of Dubai, nothing should be taken for granted.