EPBMs to usher in metro travel in Xi'an
EPBMs to usher in metro travel in Xi'an May 2010
Desiree Willis, Technical Writer, The Robbins Company
Metro tunnels for China's ancient city of Xi'an will move commuter travel from surface streets to below ground. Two 6.2m (20.3ft) diameter Robbins EPB machines are on track to bore under the 3,100 year old city, well known for its cultural artifacts including the terracotta warriors. The machines will excavate Lot 12 of Xi'an's Metro Line 1.

Spoke-type EPB cutterhead

Assembly of the first machine was completed in March at a nearby manufacturing facility in Chengdu, and it was launched on April 28. China Railway 11th Engineering Bureau Group Limited signed a total supply contract with Robbins in June 2009. The second machine will be launched in May 2010.
The Robbins machines will excavate twin 2.3km (1.4 mile) long tunnels, and pass through four cut-and-cover stations from Kangfu Road to the Chang Lepo are. The two TBMs will be the first to start excavation on Line 1, and will be followed by eight other machines excavating their own respective lots.
Both Robbins machines are customized to suit the local geology that includes sand, pebbles and clay with significant ground water content. Spoke-type cutterheads and 800mm (32in) diameter shaft-type screw conveyors will aid in efficient advance while maintaining a water-tight seal and balanced earth and water pressure excavation.

First Robbins launch on April 28

The line will pass nearby a number of ancient structures, including a bell tower and city wall dating back to the 12th century. Due to the sensitive area, city regulations stipulate a maximum of ± 15mm surface extrusion or settlement on tunneling projects. Subsidence and vibration will be carefully monitored throughout excavation to avoid any structural disturbances.
Once complete, the 26.4km (16.4 mile) long metro Line 1 will travel from north to south through downtown areas of the city. The city is currently reliant on surface transportation only-the underground line is estimated to reduce traffic times across the city from well in excess of an hour to 39 minutes. Line 2 of the Xi'an metro is nearing the end of its construction towards being operational in 2011. Three more lines are planned for excavation in the next five to seven years.
Outline of the Xi'an metro masterplan

Outline of the Xi'an metro masterplan

Construction of the first mass transit line for the city, Line 2, began along Chang An street in September 2006. Running north-south from the new Xi'an North Railway Station to Weiqu South, some 23.5km of the 26.4km line is underground, about 20m below the surface, in twin running tunnels that pass close to or under historic sites including the famous Bell Tower and the ancient city wall. Estimated at 17.9 billion Yuan (US$2.24 billion), the line and its 20 stations is schedule to open in 2011 and cut to travel time across the city in half to about 40 minutes.
Construction of the 2nd route, Line 1, was scheduled to start in later 2009 it is reported, but was brought forward by a year as part of the Chinese central government's stimulus package and response to the 2007-2009 financial crisis. The two Robbins EPBMs start the underground construction of this east-west line, which is scheduled to be complete by 2013. An extension of Line 1 is planned to start in 2011 and be completed also in 2013.
Construction of the Line 3 is planned to begin after 2010. It comprises a planned 44.3km (27.5 miles) of track and 30 stations. When completed, the total system is expected to span a combined route of 251.8km (157 miles).


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