Besix unleashes monster Garhoud span

Traffic congestion is one of the biggest problems that Dubai currently faces. And in an attempt to meet the need for road infrastructure, the Garhoud Bridge extension is underway. Christopher Sell reports.

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By  Christopher Sell Published  November 25, 2006

|~|147proj200.gif|~|One of the main construction challenges on the bridge is the shape of the 12 piers being used to hold up the structure. According to Dessoy, the x,y and z axis of each one differs. To achieve a physical result (above), AutoCad was used to develop a model, which was used to fabricate a mould to cast each pier.|~|For the thousands of drivers who must cross Dubai Creek on a daily basis, traffic jams are a way of life. Thankfully, it has not escaped the attention of the municipal authorities that transport is possibly the most pressing issue facing the emirate and its future development.

The Roads and Transport Authority (RTA) has, under the direction of HH Sheikh Mohammed Bin Rashid Al Maktoum, initiated a swathe of major projects designed to reduce the pressure on Dubai’s increasingly congested road network and eliminate a number of notorious bottlenecks.

Of these, the most high-profile is the first phase of the much anticipated Metro. Worth US $4.2 billion (AED15.5 billion) and covering 35km, the Red Line, between Salahuddin Road and the American University in Dubai, and the Green Line, from Dubai International Airport to Rashidiya bus station, will be completed by May 2009. Extensions to both routes are scheduled for the second phase, which is expected to be functional by 2010.

Complementing this project is the 12-lane Ras Al-Khor crossing linking Dubai Festival City and Interchange One, and the floating Creek bridge. The final piece of the puzzle is the Garhoud Bridge extension – a 14-lane crossing, due to open in February 2008, designed to replace the existing six-lane crossing.

Work begun in February 2006 and is due to take 741 days to complete at a cost of $113 million. The new Garhoud Bridge extension will aim to alleviate congestion at one of Dubai’s most notorious bottlenecks. The contractors for the project are Besix, with Halcrow acting as consultants.

To span the creek, the extension will form two seven-lane bridges, both 16m high, which will allow uninterrupted access for boats travelling through the Creek, eliminating the need for the bridge to be closed and raised to allow boats through the Creek – a time consuming and costly procedure (at $1,300 per opening).

After the cofferdam was created using sheet piles, construction work on the piers and deck began in earnest. Once the concrete is poured, post-tensioning is applied to each section. This takes one week to complete, and one section of 80m between each pier is expected to take four to five months. Each pier will feature 24 piles at 1.5m thick and 28m long. Once the post-tensioning has taken place, the scaffolding is removed.

The project, however, doesn’t just pose immediate construction challenges, it has to factor in the consistent traffic flow that uses the bridge – and Besix is acutely aware of the complexity of manoeuvring traffic flow from one lane to another. “The complexity is that we will have to shift the traffic from the existing bridge to the new bridge, which will be 15m higher. That will be a major challenge – moving it in sequence without stopping the traffic,” explains Philippe Dessoy, deputy general manager of Besix subsidiary, Six Construct.

To overcome this, in November 2007, traffic coming from Dubai on Sheikh Rashid Road will be diverted onto the south side of the extension, while traffic flow from Garhoud will continue over the existing road. And between November 2007 and February 2008, traffic coming from Sharjah will be re-routed onto the southern section of the bridge, capitalising on its seven-lane capacity. The completion of the overall project is estimated to be February 2008, with the old bridge being demolished in March. But as yet, the method to carry this out has not been decided upon.

The logistics of such an operation are compounded further by the fact that numerous services use the bridge to connect Bur Dubai to Deira. A new corridor will be created that will enable the various utility services to connect up without any shut-off incurred.

Although a simple construction process, it has nevertheless proved taxing from a logistics point of view, with outside influences inevitably proving troublesome. Notably, the rising price of raw materials has resulted in Besix making a loss on steel. “We need 20,000 tonnes of steel for this project, but the market is so volatile that the price of steel rebar has gone up 25% since we were awarded the contract. In Dubai, it is now a risk for the contractors on most of the contracts,” says Dessoy.

A further 120,000m3 of concrete was used together with 60,000m3 for the approach. The bridge utilises a special concrete mix called GGBS – an homogenous mixture that is very dense and prevents against attack of chlorides and is a highly durable concrete for marine environments. However, it is much more expensive – 30 % more than conventional bridge concrete mix.

Dessoy adds that time-dependent nature of construction is one further issue that impacts on a number of facets of the construction phase: “The speed of the project is another challenge. That kind of project would take three years in Europe. We are doing it in just 700 days [two years].” To overcome this the team is currently employing approximately 1,150 labourers on-site working double shifts, and compressed works schedules.

Bridge aesthetics bring further challenges to the team. “The shape of the pier is so difficult, it is not just rectangular or circular with a defined geometry, this geometry is very unique,” says Dessoy, adding that it’s x,y and z axes all differ. To achieve a physical result, AutoCad was used to develop a sophisticated computer model, which was used to fabricate a mould to cast the pier.

Complications do not cease at this point, however. Such is the shape of the pier, that once cast there is a significant temperature variation between the core of the structure and the exterior surface – a disparity that could lead to cracking if not treated. To overcome this, thermal modelling is used, a process whereby a coolant is applied to the exterior of the pier, before rockwool insulation is added to prevent the temperature variation (the core temperature is 68°C following casting) from being too marked. The rockwool will stay on for approximately one month before it can be removed.

“From start to finish it has taken five weeks for the first pier but we are hoping to speed up to three weeks for the next ones as we get used to it,” adds Desoy. There will be 12 piers in total, six on each bridge with 80m between each one.

Besix also recently received news that it has submitted the lowest tender for the $130 million contract for major road improvements to the main Dubai-Sharjah highway. The contract will cover the widening of the existing road, the construction of a new underpass and an extension of an existing underpass.

With more people landing in Dubai every day, it can only be hoped that the bridges and other transport schemes achieve what they have been built for. Otherwise traffic and congestion in the city will surely reach untenable levels. A situation neither residents nor the Dubai Municipality would welcome.||**||

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