Desiree Willis, Technical Writer, The Robbins Company

A new 10.2m (33.5ft) diameter Robbins EPBM is planned to tunnel directly underneath urban areas for Mexico City Metro's Line 12. The machine will be the largest diameter TBM ever to bore in Mexico.

Robbins contract with the ICA Consortium (consisting of Empresas ICA, Cicsa, and Alstom SA) is for the machine, its back-up system, and cutting tools. The machine will be designed and built by Robbins in both U.S. and Chinese facilities. Launch of the EPBM is scheduled for Autumn 2009, and the new line should be operational by the end of 2011.

The machine will excavate a 6.2km (3.85 mile) tunnel between the Mexicaltzingo and Mixcoac areas in clay and sand, with boulders predicted up to 800mm (30in) in diameter. A specially designed 1,200mm (4ft) diameter two-stage, ribbon-type screw conveyor will ensure efficient removal of the large boulders.

The machine will feature active articulation for smooth driving around curves, including a tight section with a planned radius of 250m (82ft). The active articulation process will prevent deformation of the segment rings on the curved portions of tunnel.

In 2007, the Mexican Federal District announced plans to build Line 12 of the Metro entirely underground. The 24km (15 mile) line with 22 stations will serve the southern area of the city. Mexico City's metro is one of the world's largest, with more than 200km (125 miles) of rail and nearly 4 million daily passengers.

www.robbinstbm.com