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Sat 14 Apr 2007 12:00 AM

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On time: precast gives ACC desired finish

Construction of the Emirates HQ building has highlighted the precast advantage.

There is a sense of symmetry with the Emirates HQ building, currently nearing completion on Airport Road. When it opens it will represent a transport hub in every sense; a building for an airline company, a new metro system, and a connection to Dubai International Airport via an underground tunnel beneath one of Dubai's busiest roads.

Two 11-storey car parks on either side of the building will provide parking for 2,400 cars. And a walkway from the building will eventually link directly to an above ground metro station. The HQ's will accommodate a range of Emirates crew processing facilities and managerial offices, and a baggage handling system.

The project is a challenging one, not just because of the range of construction techniques being practiced, or that it is taking place in the shadow of a major international airport, but also for the numerous contractors working on site. However, despite a small delay of three months - due to the late naming of sub-contractors - work is due to be completed in June of this year.

The main contractor for the site is ACC - in a contract worth US $144 million (AED530 million) - while WJ&P is the main contractor for the underground tunnel that will link the HQ building to the airport. Dubai Rapid Link Consortium is responsible for the work on the metro and Arcon is the main consultant. Together with a raft of subcontractors, there is an average of 1,250 people working on site.

Construction efforts are currently being focussed on the marble work for the ground and first floor, waterproofing of the roof, and completion of the cladding sections of the main building. The bridges for entry and exit to the building are also currently under construction, and due for completion in June. These ramps are being built using differing techniques.

According to Ziad Awji, project manager, ACC, the exit ramp is being built using a decking and backfilling method, while the entrance ramp is a conventional scaffolding technique. While Awji explains that backfilling is the preferred technique for the entrance ramp, as it is 50% quicker, the ramp up is located over the basement and the loads would have been too high. The road system will enable buses to drive from Airport Road up to the second floor of the building via ramp ways. This involves building approximately 500m of single-lane roadways up to 8m high.

Awji says that ACC is currently waiting on delivery of specially constructed building pads from Italy, which should be arriving this week. The fourteen pieces, which weigh 700kg each, will be fitted to alleviate vibration between the pier and the road. Once the pads are fixed, which should take two weeks, stressing will begin for the post-tension. The post-tensioning designer is MEPS.

Awji explains that the original design called for the car parks and main building to be built using post-tension, but it was recognised that precast would be a more suitable approach to take, and would take three months off the build schedule. This also had an added aesthetic benefit: "In the car park we changed to precast; it is easier for the finishing. I don't like to do concrete and plaster from the outside - with precast you get a much better finish," he says. As construction for the car parks was delayed, this re-design was possible. But the main building remained the same, since there was no time to redesign it and get permission from Dubai Municipality.

No redesign would have allowed the building to be any higher, however, due to its proximity to the airport. "We wouldn't make it taller, you cannot go one centimetre more. It is very strict because we are close to the airport."

Interestingly, for construction purposes, Awji says that permission was obtained from DM for cranes that breached the imposed height limit. Nine tower cranes at a height of 75m were used during the construction. Now there are four remaining, two in each car park, to fix the precast slabs. These will be dismantled this week. By the time construction is complete, 159,000m

of concrete provided by Abu-Dhabi based TransGulf will have been used, together with 20,000 tonnes of steel.

With so many contractors, some negotiation was required with regards to schedules, particularly since Awji was not aware of the metro when he began planning the project. "It wasn't a problem; they followed my programme, not their programme. At the beginning they said to follow them, but I said no way, as our contract was due to start first. So they agreed to start three months later." At present, the pilings for the piers have started and the excavation for the station has begun. While the station will alleviate congestion, until the metro is open, traffic flow around the site will be high, as traffic cannot exit onto Airport Road.

The metro stop - known as Emirates - is to be the penultimate stop on the Red Line before the airport and will act as a significant transport hub for the 6,000 workers expected in the building.

The above-ground station will connect directly to Emirates HQ building via a walkway to the second floor. When completed, the project will facilitate the departure and arrival of Emirates' crew as well as provide administration space for the rapidly expanding airline.

With such disparate elements on the project - from tunnelling under the Airport Road to dealing with a range of consultants and contractors - to be more or less on schedule is a laudable effort. And these efforts are compounded when you consider it is taking place opposite the expanding Dubai International Airport and is situated on a major road network.

Cut and cover: tunnel will connect HQ with Terminal Three

Work on the tunnel began on site in August 2005. The client for this part of the development is Dubai Civil Aviation (DCA). It will be 250m in length and run from the Emirates HQ building basement into the airport, where it will connect with the Concourse Three building.

A cut and cover method is being used, which sees an open excavation method to build the tunnel before it is covered. To achieve this, Airport Road was diverted northwards, and on completion of the first section, traffic was diverted in front of the ACC building. In all, Airport Road has been diverted three times as various sections of the tunnel near the building have been completed.

The maximum depth of excavation is 17m and will require a total of 200,000m

of earth to be moved by the time the tunnel is finished.

According to Andreas Kannas, project manager, WJ&P, one of the main construction challenges of the tunnel project is tackling the combination of multiple underground utilities, such as telephone, water pipes and irrigation. De-watering was also a factor that had to be considered.

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