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Desert spring

Middle East Dubai Marina

In 10 years it is hoped more than 100,000 people will live along the banks of Dubai Marina. SteveTurner went to see how the ambitious project is developing.

The visitor centre of Dubai Marina paints a stunning picture. Videos show palm trees blowing in a gentle breeze, with unspoilt beaches stretching as far as the eye can see. 'A new concept of living in the Middle East is being born - there is no other place like it.'

The residential and leisure complex, being developed by Emaar Properties, is sited just to the west of Dubai city based around a 3km long manmade canal. On the 6M. m 2site, numerous luxury tower blocks and apartments will reflect traditional local architecture.

First off however was Halcrow International Partnership, responsible for structural marine design work of the canal, along with hydraulic modelling to assess how the development will affect local tides and currents.

Earthworks started in late 1998, followed by work on the quay wall in mid-1999. Dewatering was the first major task for contractor Al Futtaim /Tarmac, a partnership between a local company and UK-based Carillion, which has been working in the region for a number of years.

With the water table in the area very high, the whole site was first excavated down to groundwater level. Foundation trenches for the quay walls were then dug, and pumped out into the sea at a rate of about 10M litres per day using up to 35 pumps The area was then taken down to full depth, the canal bed being 4m to 5m below the ground water level.

Of the 5M. m 3of material excavated, 1M. m 3has been taken off site, with the remainder being reused around the development, or stockpiled for future use.

The mass concrete block quay walls stand between 7m to 8m high on a crushed rock foundation, behind a layer of anti-scour protection rock at the toe, contained by a geotextile membrane. The canal is deeper at the ends to allow larger boats to enter.

All the 11,400 blocks used, weighing between 35t and 45t each, were cast on site at a rate of over 50 blocks a day, stripped after 10 hours and water cured for 14 days. Coping blocks were secured using stainless steel dowel bars.

Halcrow project manager David Aldis described the casting process as a 'total success' adding that, 'not one of the blocks had to be rejected.'

Water is allowed to flow freely under the wall through the rock foundation ensuring no build up of hydrostatic pressure from tidal fluctuations on either side.

On completion a throughflow of water in the canal will ensure that any pollutants are flushed round and out, and that water will not stagnate. Computer modelling by Halcrow showed that the canal will flush itself naturally every 10 days. And sedimentation will not be a problem, as the analysis showed that currents will be so slow that very little material will be carried in.

As the client wanted an early start to marketing the project, it was decided to flood half the canal to improve the visual appeal, and therefore the selling power of the apartments.

A sheet pile bund was formed just over a third of the way along the canal. This was then ramped with sand with a stone blanket placed on the upstream side to protect against scour and to make it traffickable.

Partial flooding was initiated as part of a special ceremony attnded by His Highness Sheikh Mohammed bin Rashid al Maktoum, Crown Prince of Dubai, with pipes configured to produce spectacular fountains while filling. Filling was completed in three days, the piles extracted and a suction dredger mobilised to remove the bund.

Construction work is now well under way on phase one of the project. Al Futtaim /Tarmac is again responsible for the civils foundation work, which involves bases for six high rise blocks of luxury flats, formed by concrete rafts on 2,632 bored and cast insitu piles, 22m deep.

Emaar project manager Maha Badr says sales are going well on the first two blocks, with the third due to start selling in the autumn. The construction team, including Halcrow, 'is doing a good job, and Emaar is pleased with their performance, ' she says.

Construction of the proposed breakwater is now out to tender, as part of the $43M marine works. It is hoped work will start in October.

Computer modelling by Halcrow show that currents along the coastline run from south to north meaning that material will be deposited on the south of the breakwater, leading to a build up. Erosion of the beach will occur to the north of the breakwater, where material is being pulled northwards by the currents.

Halcrow has devised a sand bypassing process to reverse the effects. Sand will be pumped under the breakwaters and channel from south to north of the entrance. The current will then take the material back in to the north side of the breakwater, preventing a build up of material to the south.

Civils work is programmed to finish in June 2002, by which time the development will be well under way. The scheme is an integral part of government plans to turn the Emirate into a leading tourist destination, and it looks like being a stunning success.

Cube roots Over 4,000 concrete cube test results have been collected throughout the contract.

The site batchers produced 700m 3of concrete a day, with chilled water and flaked ice used to bring the concrete temperature down during batching of the 40kN, 370kg mix.

Work on the walls was halted from January to May while live services were diverted, and interestingly it was found that higher strengths were obtained by cubes produced from cement that had stood and cooled in the silos during the winter months.

Aggregate and rock was gabbro from the nearby Hajjar mountains.

Average strength of the cubes at seven days was 45kN/mm 2(last 100 using hot cement 42kN/mm 2). At 28 days it was 54kN/mm 2(last 100 using hot cement 53.5kN/mm 2).Standard deviation of cube strengths throughout the contract was less than two.

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