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The extraordinary Palm Islands project in Dubai is throwing up some extraordinary ground engineering. Adrian Greeman reports.

Building a whole island is some conceit, especially one in the shape of a palm tree.

To build two is yet more daring, but even that was not enough for a Dubai development company, which now plans a third project of artificial islands.

'No one has done reclamation quite like this before, ' says Bob Berger from project management company Hill International. 'Not on this scale anyway.'

Berger is overall manager for Dubai development company Nakheel, which is marketing its Palm Island projects as the 'Eighth Wonder of the World' They are certainly among the biggest residential schemes in the world, with costs for the first phases of $2bn and $2.5bn respectively - though even that can seem 'normal' in Dubai, where massive development is under way right along the shoreline and far into the desert hinterland.

Berger is overseeing half a dozen other major retail and tourist developments for Nakheel, but the Palms are the most ambitious, aimed squarely at the world's top-end tourist and leisure market (see box). David Beckham and other footballers have already bought villas.

Each island consists of a thin circular or crescent-shaped reef which acts as an outer sea barrier around the 'palm tree' The 'trunk' connects the island and its spreading 'fronds' to the shore. The first scheme, the 5km diameter Palm Jumeirah, is 20km along the coast from Dubai;

the second, Palm Jebel Ali, is another 10km onwards, just past the Jebel Ali container port.

A third project just beginning 4.5km offshore is 'World Island' a collection of 260 small islands grouped into the shape of the world map, all surrounded by a 7km wide, 9km long breakwater. Each island will be sold as an individual estate.

The two Palm Islands have been steadily rising from the seabed just offshore. Construction began on Jumeirah first, in May 2001. Jumeirah finishes next year and Jebel Ali in 2007.

'We began planning in late 2000, ' Berger says. Contracts to Archirodon of the Netherlands for the breakwater design and construction, with Royal Haskoning and Van Oord also picking up work.

'We, and the contractors, commissioned hydraulic and ecological studies including 2D and 3D modelling of the sea flows at Delft Laboratory in the Netherlands.

'One result was a change in the breakwater concept which now has two openings to allow flushing of the lagoon. It seems to be working out as hoped because there is no algae or the like developing.'

The island embankments are relatively simple, sand fill placed directly on to the seabed, up to 10.5m down, with bottom dump dredgers and 'rainbowing' as the levels rise to the final height of 3m above water, 4m on the crescent.

Berger says the seabed is similar to the land, consisting of firm layers of calcerous material and soft sandstone.

Work like this has been done before, he says, but not to the placing accuracy needed, particularly for World Island. Without the recent development of GPS control systems for modern cutter suction dredgers, he does not think it would have been possible, 'particularly for the 5m wide beach sand strips. Remember we only have two straight lines on the whole project' Placement of 95M. m 3of fill for Jumeirah finished last autumn and about 20M. m 3of fill has so far gone into position for the 40% larger Jebel Ali. Of the seven major dredgers, 12 transport barges and seven crane barges used here, many are now working on the World project.

Berger says the most complex work was for the outer crescent which is armoured with boulders of up to 6t placed over smaller rock layers.

These sit behind an initial rock toe bund on the seabed, placed mainly by barge-mounted excavator grabs. The rock layers add another 5M. m 3to the overall quantities. Most of it was trucked in from mountain quarries 100km away.

'One interesting aspect of work is the profusion of sealife, from plankton to dolphins, that has arrived, ' says Berger. In many ways the seabed is a reflection of the desert, with little growing - 'But we seem to have stirred up nutrients.'

Providing something for life to grab on to seems to have an effect too, and eventually it is hoped coral can be induced to grow. Three old aeroplanes, stripped of toxic materials, are being sunk in the water in the hope of promoting sealife growth as part of a diving centre.

Berger says the formed ground is good and differential settlement will not be an issue.

Teams of vibro-compactors are working their way along the island branches; Bauer, Soletanche and Keller Group are among the companies consolidating the ground before infrastructure work gets going in earnest.

Keller UK marketing director Martin Singleton says its £8.2M contract, which started in February, involves densifying the ground to a maximum of 11m, virtually the full depth of the reclaimed sand. Keller has up to 10 fully instrumented vibro rigs working on its section, using seawater flushing which helps form an annulus around the holes to allow sand fill to fall to the bottom.

'You are basically evening out fluctations in the bearing capacity, in this case to give an overall 150kPa. It means the client does not need to decide exactly where his building will go yet and eliminated piles for most of the development, ' Singleton says.

Each island is 'a small city' and needs all the ingredients of a normal urban environment plus the extras that the desert demands, from freshwater provision, total irrigation and major cooling.

'We have nearly everything there except nuclear power, ' says Berger. 'We even considered wave and wind generation.' But wave action is never large enough because the Arabian Gulf is too short to allow major storm systems to develop. That is good news for the breakwaters, of course.

Dubai's power stations will supply electricity, though the islands will have their own water distilleries for part of their supply. They will also have their own cooling systems: chilled water for air-conditioning in villas and apartments will be supplied from a central plant via special insulated pipes.

These larger plant items will be piled, as will one or two of the biggest apartment blocks up to 14 storeys high.

'We also have to install telecommunications, the electricity distribution from 132kV down, and roads, ' says Berger. There will be a five-lane dual carriageway entrance road which runs across the the 300m long 'tree trunk' bridge to the mainland.

A design competition for this 350m long Yshape gateway - it splits into two roads on the island - was recently won by H2L2 architects of New York with a scheme using 25m high space frames on either side and incorporating statues of the seven original wonders of the world.

Germany's Leonhardt, Andra & Partner is structural engineer. Contractor Belhassa Six has already begun piling foundations.

The green epoxy-coated rebar cages it is using are a typical feature in Dubai, which has one of the world's most aggressive groundwater environments. Nearly all foundations need extensive protection.

Jebel Ali will also have side bridges from the ends of the crescents to the shore and each development will have tunnel connections at the top of the 'tree' across the lagoon to the crescent and its roads.

Various infrastructure contractors are now moving in, as well as workers for the various private developments as plots are let for hotels and apartments.

With everything due to finish on Jumeirah by the end of 2005, Berger's multinational management team has a major task of co-ordination on its hands.

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