Tunnelling started on Xi'an Metro Line 1

New metro tunnels in Xi’an, one of China’s most ancient cities, will move commuter travel from surface streets to below ground. Two 6.2m diameter Robbins EPBs will excavate Lot 12 of Xi'an Metro’s Line 1, boring under the 3,100 year old city. Assembly of the first machine was completed in March at a nearby manufacturing facility in Chengdu, and was launched on April 28.

The Robbins machines will excavate parallel 2.3km tunnels, and will pass through four cut and cover stations stretching from Kangfu Road to Chang Lepo areas. The two TBMs will be the first to start excavation on Line 1, and will be followed by eight other machines excavating their respective lots.

Both Robbins machines are customized for geology including sand, pebbles and clay with significant ground water. Spoke-type cutterheads and 800mm diameter shaft-type screw conveyors will aid in efficient advance while maintaining a watertight seal and balanced pressure.

China Railway 11th Engineering Bureau Group signed a total supply contract with Robbins in June 2009. The second machine will be launched in May 2010.

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 metro Line 1 will travel from north to south through downtown areas of the city. Line 2 of the Xi’an metro is currently under construction and will be operational in 2011. Three more lines are planned for excavation in the next five to seven years.