Mexico City Metro tunnel - TunnelTalk
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Onsite assembly in Mexico for Robbins EPBM Jan 2010
Desiree Willis, Technical Writer, The Robbins Company
Mexico City officials celebrated the completion of the country's largest ever TBM with a cutterhead turning ceremony last week (January 7, 2010). The 10.2m (33.5ft) diameter Robbins EPBM will begin excavation in the first week of February.
p3

Site build in tight launch shaft

The 7.7km (4.8 mile) long tunnel for the Mexico City Metro represents the city's first new route in ten years, and will service thousands of passengers daily.
The giant machine for the ICA Consortium (ICA, CARSO, and Alstom) was assembled at the jobsite in a 17m deep launch shaft. Crews assembled the machine in a concrete cradle at the shaft bottom, using gantry cranes to lower in components including the forward and rear shields, cutterhead, and screw conveyor. Testing of all sub-assemblies is currently underway.
The machine is the first-ever EPBM to be assembled at a jobsite using Onsite First Time Assembly (OFTA). The Robbins-developed process allows TBMs to be built initially on location, rather than in a manufacturing facility, a process that eliminates in-shop assembly and disassembly time as well as costs for shipping larger, partially assembled components. "With proper project management and fit up of components, OFTA can save about 70% to 80% of the time required for a similar assembly at a shop," said Ismail Benamar, Tunnel Manager for ICA.
The small launch shaft of about 34m long by 14m wide, is located in one of the most dense urban areas of the city. Machine launch in the tight space
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Mexico City's new Line 12 alignment

will require the TBM to excavate the first 70m of tunnel using umbilical cables connected to back-up gantries on the surface. Gantries will be lowered into the shaft successively as the machine bores forward.
Ground conditions in Mexico City require extensive vibration monitoring. Layers of clay, sand, and boulders up to 800mm (30in) in diameter are expected, as the area is part of a drained lake bed. The machine is designed to fit the conditions, utilizing a two-stage, 1,200mm (4ft) diameter ribbon-type screw conveyor to handle the large boulders. The machine will also feature active articulation, used to prevent deformation of the segment rings on curves as small as 250m (820ft).
In 2007, the Mexican Federal District announced plans to build Line 12 of the Mexico City Metro. Due to go online in 2011, the 24km (15 mile) long route will pass through 22 new stations between the Tlahuac and Mixcoac neighborhoods. The Mexico City metro is one of the world's largest, with more than 200km (125 mile) of rail and serving nearly four million passengers daily.
References
Mexico's largest EPB to be supplied by Robbins - TunnelTalk, Oct 2008

           

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