Shani Wallis, TunnelTalk

Whisper quiet driverless trains

Billed as one of the most expensive and advanced in the world, the Dubai Metro system met its planned inauguration date of the ninth day of the ninth month of 2009, and welcomed its first customers on Wednesday. Anchored by a 13km long underground section in the city centre, the 70km system on two initial lines took five years to build and cost more than a reported US $7.6 billion. Built for the State's Roads & Transport Authority (RTA) by the DURL turnkey consortium, the civil structures are procured as a design-build contract with consortium partner JTM JV, and with Atkins engaged as the contract's detailed design engineer. DURL partner Mitsubishi Corporation supplied the rail-systems. The Systra/Parson JV provided a reference design for the construction contract and is managing the project through the construction phase as the Engineer on the project for the RTA. Serco, the same operator as for the Docklands Light Railway in London, the Great Southern Railway in Australia and the Copenhagen Metro in Denmark, has the concession to operate and maintain the first two lines of the system for an initial 12.5-year period.

Dubai Metro first phases

On its inauguration this week (9 September 2009), riders were treated to first class mass transit experience with sleek blue and silver driverless trains gliding along elevated, at grade, and underground trackway in what is described as "whisper mode" and offering air conditioned comfort in the trains and in the underground stations.

The opening this week is the beginning of a phased start-up programme. Services began on the 52.1km long Red Line with the first 10 of its 29 stations (four underground) ready for business. The remaining 19 stations are to be opened over the coming months as surrounding developments come online. The first 7.9km of the 23.9km long Green Line, with six of its 14 stations underground and two interchange stations with the Red Line, is set to open in March next year (2010).

Ground conditions for the total 13km underground sections of the two lines, including two underpasses of the Dubai Creek, were described as extremely aggressive, comprising mainly loose to medium dense, high permeability marine sand; cemented sand Sabkha deposits, with some hard concretions and voids; underlain by calcareous and gypsiferous sandstone and siltstone; and all under a high water table of hyper-saline groundwater.

With no previous experience of large diameter EPB tunnelling in Dubai a trial drive on the Red Line was implemented to validate design assumptions and monitor excavation experience.

System build-out ambitions

The underground alignments are single-tube double-track tunnels of 8.5m i.d. which were excavated in 10 drives using three 9.5m diameter Mitsubishi EPBMs. Four drives radiated from Union Square and continued after being 'walked' through excavated station boxes, and two on the Green Line were driven from Palm Deira and Al Ras. To provide for a 100-year design life, the tunnels are lined with a bolted, one pass precast concrete segmental lining that has a flexible epoxy coating applied to the external surfaces and dual EPBM and hydrophilic strip gaskets in the joints.

Muck haulage behind the machines was by continuous conveyor with vertical conveyors in the shafts. A two-part annular grout was injected through the tail skin. Ground conditioning foam was injected into the excavation chamber and a second screw conveyor ensured maintenance of face pressures in the cohesionless soils. Average progress was 10 rings or 15m.day with a maximum production on a singe 24hr period of 21 rings or 31.5m. The stations are all open cut excavations supported with slurry diaphragm walls.

Construction of the first two lines of the Dubai Metro, the first in the Middle East, was started on the fifth day of the fifth month of 2005, at a time when the economy of the State was booming. Much has changes in the meantime but still the investment of nearly US $8 billion is expected to generate the expert axiom return of $3 in business sales for every dollar invested in modern rapid transit.

RTA is also advancing plans for four new lines - a Purple Line of 49km; a Blue Line of 50km and Palm Deira Yellow and Black Lines of 26.5km total.

References

Dubai Metro website