The joint venture contractor building Line 12 of Mexico City metro is to use a 10.2m diameter Robbins EPBM for the excavation of the western section of the line.
Geology along the 6.2km long alignment, between Mexicaltzingo and Mixcoac in the south west of the Mexican capital, comprises clay and sand with large boulders, predicted up to 800m wide.
Robbins is building the shield in the US and China, and the TBM will have a 1.2m diameter, two-stage ribbon type screw conveyor to deal with the large boulders.
The EPBM will be the largest ever TBM to be used in Mexico. It will also have active articulation for building tight curves (250m radius) without deforming segments.
The JV contractor is led by Ingenieros Civiles Asociados SA (ICA) with Carso Infraestructura y Construccion (Cicsa) and Alstom Mexicana as partners. It has contracted Robbins to deliver the TBM, back-up and cutting tools, and plans to launch the shield in the third quarter of 2009, and the new metro line is to be commissioned before 2012.
Line 12 was approved for construction last year and will be approximately 24.5km long in total. The line will run from Mixcoac in the west, which will interchange with Line 7, to Tiahuac in the east. There will be about 20 stations.
In the stretch to be tunnelled by the EPBM the intermediate stations are Insurgentes Sur, 20 de Noviembre, Zapata (interchange with Line 3), Parque de los Venados, Eje Central and Ermita (interchange with Line 2).
The eastern section of Line 12, from just beyond Mexicaltzingo, is to be commissioned in advance of the tunnelled section – by 2011, said the client, Metro de la Ciudad de Mexico. It awarded the Pesos 15.3bn (US$1.17bn) fixed price, fixed term contract, excluding VAT, to the JV in July. The bid was submitted in late April.
