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Building on top of the UAE's first rail system

When people tell you that Jumeriah Palm Island is the smallest of the artificial islands built on the coast of Dubai, all things are relative.

Despite been an eighth of the size of the largest offshore developments planned, it is still 5 sq km of prime real estate.

The basic superstructure was created by spraying dredged sand onto the seabed to form the palmshaped island which is then protected by a breakwater crescent, comprised of 7 million tonnes of rock.

The monorail that serves the island is the UAE ’s first mass transit rail project, due to come on stream in April, five months before the main metro system is open.

The monorail will run the length of the 5 km artificial island, bringing thousands of visitors a day to the Atlantis hotel complex at the top of the ‘tree’ via two smaller stations along the way.

A congested site is not a problem you normally encounter in Dubai where there always more desert to build on. But that is the key challenge for Mott MacDonald in its work on the Gateway project – the monorail station and tower complex at the ‘foot’ of the tree.

Tight site

Hemmed in on both sides by road bridges only 10 m away and with a soon-to-be-working station underneath, building towers doesn’t come much more onerous than this.

The main station at the foot of the trunk obviously has to be operational for the April opening but that is not the extent of the challenge. The podium housing the station and workshops is also the base for three towers, a mix of offices, residential and the headquarters of developer Dubai World - the tallest is 55 stories.

All sat on top of one of the world’s biggest underground car parks housing 5,000 cars. The 12 storey podium is due to be finished by the end of next year with the towers complete in 2010.

Mott MacDonald has a site assurance role on the building for client Nakheel (the main contractor is Japanese company Taisei) which started about 18 months ago. Project director Rod Williams says: ‘Having worked withus on the civils side, the client wanted some further experience for the building side.”

Time has been crucial on the project with the monorail contractually required for the full launch of the Atlantis resort (built by Laing O’Rourke) in the Spring.

This meant the groundworks and foundations for the whole project – built to LEED Gold Standard - had to be started well in advance of final designs for the towers that would sit on top of it.

Having to start in the ground when the three towers usage hadn’t been finalised was a challenge. As the design has evolved the effect on the structure of the podium has been considerable.

Additional piles, and piles of larger load bearing capacity, have been used in the podium’s foundations, while a 3.5 m thick reinforced concrete floor slab within the podium has enabled significant freedom to change the position and loadings of the towers above. The project is founded on 980 piles in all.

There are 3,000 workers on site with cladding and fit-out of the podium starting last month.

Noise dampening

Because the tower nearest where the trains will enter is also residential, noise dampening was important.

The project used precast sections so beams could be isolated from the main structure and placed on heavy rubber mats to further dampen vibration.

As Mr Williams says; “It is a very congested site and getting more congested as the developments move on and the station gets ready to open. Health and safety is a key concern because you have a public interface with a building site – not unusual in terms of London but it is unusual in Dubai which tends to be new build.”

All this isn’t to say that the monorail itself wasn’t a challenging project as well. As Mike Barron at Mott MacDonald, says: “First the regulatory authority didn’t exist and when it did exist we didn’t know how it was going to certify the rail system. Only now, not much more
than six months ahead of being operational, are we at a point where it knows.”