The front end of the Al Bugeisha that will arrive in Dubai next month.
Metro tunnelling work set to begin
Dubai’s ambitious multi-billion-dollar transport project – the Dubai Metro – is set to enter a new phase with tunnelling works set to commence early next year.
01 October 2006
The tunnelling work for the multi-billion-dollar Dubai Metro project will be all set to start next January when the Al Bugeisha – the tunnel boring machine (TBM) that’s been assembled in Japan – is shipped to Dubai next month (November).
The massive, much-anticipated project, estimated to cost Dh15.2 billion ($4.2 billion), will be undertaken in two phases with the first phase expected to be completed by 2009 and the second phase 12 months later.
The TBM is used to excavate tunnels in a circular cross-section through a variety of geologies. It is manufactured to bore through hard rocks or sand layers and almost anything in between. The TBM has been named ‘Al Bugeisha’ after the small jumping desert rodent of Asia and North Africa, known for its characteristics of burrowing.
“The Earth Pressure Balance (EPB)-type TBM designed and assembled for Dubai Metro has a diameter of 9.56 m, is 82 m long and weighs 1,000 tonnes. The cutter head will have a revolution speed of 0.1 to 1.82 rev/min,” says Adnan Al Hammadi, director of the Construction Department – Rail Agency, Dubai Road Transport Authority.
“The boring for the project is scheduled to commence in January, 2007 at Union Square towards BurJuman for the Red Line. The tunnelling will pass under the creek up to a length of 1.6 km and at a maximum depth of 30 m,” he adds.
“Residents will not feel any impact of tunnelling work because there will hardly be any vibration,” Al Hammadi adds.
A TBM consists of a shield (a large metal cylinder) and trailing support mechanisms. A rotating cutting wheel is located at the front end of the shield. Behind the cutting wheel there is a chamber where – depending on the type of the TBM – the excavated soil is either mixed with slurry (so-called slurry TBM) or left as-is (earth pressure balance or EPB shield). The choice for a certain type of TBM depends on the soil conditions. Systems for removal of the soil (or the soil mixed with slurry) are also present.
Behind the chamber there is a set of hydraulic jacks supported by the finished part of the tunnel, which are used to push the TBM forward. Once a certain distance has been excavated (roughly 1.5-2 m), a new tunnel ring is built using the erector, which is a rotating system that picks up precast concrete segments and places them in the desired position.
Behind the shield, inside the finished part of the tunnel, several support mechanisms that are part of the TBM can be found, including soil removal, slurry pipelines if applicable, control rooms, rails for transport of the precast segments, and others.
TBMs are used as an alternative to drilling and blasting methods and have the advantages of minimising disturbance to the surrounding soil and producing a smooth tunnel wall. This significantly reduces the cost of lining the tunnel, and makes them suitable for built-up areas.
The mass transit project will be the major commuter artery for the city and will comprise a total of 70 km lines. It will, when completed, be one of the longest metros in the world. The Dubai Metro will have 42 stations, including nine underground stations. A total of 87 trains with a passenger capacity of 600 commuters each will operate across the emirate of Dubai at intervals of 225 seconds, reduced to 90 seconds during rush hours. The trains will be completely electronic and each of the state-of-the-art station will have its own car park, taxi stand and bus stop for rapid changeover.
