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Dubai’s rapid solution to its soaring growth

Atkins is overseeing the construction of a 75 km metro system for Dubai – a project which is proceeding at a spectacular pace

Client Roads and Transport Authority Rail Agency
Design and build contractor Dubai Rapid Link Consortium (DURL)
Civil contractor Japan -Turkey Metro Joint Venture
Civil design consultant Atkins
Engineer Systra-Parsons JV
Rolling stock Kinki Sharyo
Total project cost AED15.5 billion (£2.15 billion)
Completion date Red line September 2009, Green line March 2010
Contract Design and build

For large images click here

Dubai is a construction utopia which many of us can only dream about. The tallest structure in the world is being built there - currently at 600 m, or 159 storeys, it will stand at over 800 m when it is finished later this year. The largest theme park in the world and the biggest airport ever built, with six runways, are yet to come.

Building and property are arguably the Emirate’s new oil, and the transport infrastructure must be able to support its development, and fast.

With no mass transit system and car use rising dramatically, it is much needed. By the end of 2006 the number of cars on the road had tripled from the start of the year, to 385,000. A rush hour journey which might take an hour on the road will take 10 minutes on the metro.

Dubai’s population is also growing by around 350 people a day and by 2010 it will be nearly two million.

The Dubai Metro will be the largest mass transit system in the Middle East when it is up and running.

Made up of two twin-track lines - Red and Green - to start with, it will also be the single longest driverless system in the world.

Delivery day is non-negotiable. The Red line must open on 9 September 2009. But while construction must be quick, it still has to be of the highest quality. It has been worked on 24-hours a day since August 2005, and Bruce Maney, Atkins’ design and programme manager, says he has never seen anything like it.

“I have worked on similar systems for the past 20 years but never have I seen one where the pace of construction is so rapid,” he says. Atkins took over the design from Capita Symonds in April 2006.

Getting the job done in such a strict time limit is not easy. A traffic restriction was put in place at the same time as construction of the metro began: no over-size vehicles are allowed to drive along Sheikh Zayed road - the Emirate’s main artery - between 6 am and 10 pm. “The biggest problem was getting it all there. We do anything we can to fast-track materials,” Mr Maney explains.

Once complete, the continuously welded track will carry trains from 5 am until 12.30 am at up to 90 kph. When both lines are open 60 km will be elevated and 13 km under ground and it will be made up of 300,000 tonnes of steel and 2.4 million cu m of concrete.

The Red line runs south-west to north-east and is 52.5 km long - similar to the distance from Heathrow to Epping on the London Underground. The Green line loops around Dubai Creek and curves through the city centre, interchanging with the Red line in two places. It will be 23 km long.

The rate of work in Dubai is such that countless viaducts rise up in places along the road, to allow for additional, unbuilt structures.

John Newby, Atkins’ project director, explains the scale of development. “There are all the permanent and temporary highways and those planned for the future, all the utilities and a number of communication systems plus the chilled water supplies to the stations,” he says.

Unknown territory

Each station will have segregated prayer rooms and each train will have a separate women’s and children’s carriage, as well as a first class section, but there are no plans to stream passengers separately through the stations.

A top-down method is being used for the 10 underground stations. Diaphragm walls in the stations are 1.2 m thick and at Union Square, one of the first stations to be built, 45 m deep. A shaft was constructed in advance, with temporary walls to launch the tunnel boring machine.

Paul Nader Abbosh, development director for Atkins Middle East, claims that there was an element of venturing into the unknown, as these were the first permanent diaphragm walls in the United Arab Emirates.

At Union Square station there were two levels of temporary props planned but ground conditions were better than assumed so the second level wasn’t needed. “We were confident about what would happen but the worry is that you hit an old well,” says Mr Abbosh, adding. “The concern is that it might collapse and throw the TBM off. We worked closely with the contractors during the design.”

The reinforced concrete walls are built using Portland cement, ground granulated blast furnace slag and micro silica for durability. The concrete is cooled with ice and in the summer pouring only happens at night.

Atkins also measured potential settlements but no underpinning was needed.

“It’s been really good. Apart from some small initial hiccups, it’s been less than 15 mm, so it’s well below average,” says Atkins deputy project director Bob Eves.

Construction is going relatively smoothly so far and the speed is impressive. But the added touches may be what might make it famous. Even the train depot at the southern tip of the Red line will be lit up from the roof so it can be seen from the sky.

“The client said he didn’t want his metro to be the same as the one in Hong Kong or Kuala Lumpur or Singapore. It’s unheard of to have this type of design,” says Chris Riches, Atkins’ design manager for over ground stations.

And the metro’s first two lines are just the beginning. 320 km of metro and 270 km of trams are planned for the city by 2020 and the rest of the - region is likely to follow.

Abu Dhabi may be next and a pan-Arab rail line could be on the cards. Mr Eves claims: “Now Dubai has one, everyone else wants one.”

Japanese TBM

Tunnelling for the Red line was completed using three 9.6 m diameter Mitsubishi earth pressure balance tunnel boring machines from Japan, creating tunnels with an inside diameter of 8.5 m.

The TBM was chosen to limit the risk of damage to the structures above and next to the drives by applying controlled face pressure and a quick advance rate of around 300 m a month as well as enabling one-pass lining completion.

The first drive was 1.5 km, about 22 m below the Dubai Creek sea level with 10 m – 13 m cover to creek bed. The water table is 3 m to 4 m below ground level. The ground is made up of marine sand, overlying cemented sand and sandstones, so is weak.

The tunnels have 400 mm thick pre-cast bolted segmental lining with ring taper. Hydrophilic gaskets and external corrosion protection coating is used. Nearly 10 km of tunnels will be created for the Red and Green lines and there are seven shafts for tunnel ventilation and emergency egress, with 14 short-mined adits to the bored tunnel, as well as 1.7 km of cut and cover tunnels in four stretches.

The over ground track

Much of the track will be over ground. On the Red line it will run along the main Sheikh Zayed road. The substructure consists of cylindrical piers supported on large diameter bored, cast in situ mono piles. There will be 1,450 piers on the Red line and 530 on the Green.

There are 30,000 viaduct segments which are pre-cast in a casting yard at the southern tip of the line. The viaduct sections, which are from 17 m to 72 m long, were chosen because they are quick to install and have a limited impact on traffic. One 32 m span is put up every two days. Spans over 44 m which go over elevated sections of road are erected by balanced cantilever using specially manufactured pairs of travellers.

For speed, eight overhead launch girders are being used to construct the 43 km of viaduct on the Red line, which lifts pre-cast segments on to the piers.

For large images click here