Mexico's largest TBM completed

21 January, 2010

Construction of Mexico’s largest ever TBM was completed in January. The 10.2m diameter Robbins EPBM was assembled for the ICA Consortium at the jobsite in a 17m deep launch shaft. It will be used to bore a 7.7km (4.8 mile) long tunnel for Mexico City Metro’s new Line 12, starting in the first week of February.

Crews assembled the machine in a concrete cradle at the shaft bottom using gantry cranes to lower in components including the front and rear shields, cutterhead, and screw conveyor. It is the first EPBM to be assembled at the jobsite using Onsite First Time Assembly (OFTA).

ICA tunnel manager Ismail Benamar said, “With proper project management and fit up of components, OFTA can save about 70 - 80% of the time required for a similar assembly at a shop.”

The TBM is designed to work in Mexico City’s harsh ground conditions. Layers of clay, sand and boulders up to 800mm (30 inches) in diameter are expected, as the area is part of a drained lakebed. A two stage, 1200mm (4ft) diameter ribbon-type screw conveyor will be used to handle the large boulders. The TBM will excavate the first 70m (230 ft) of the 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.

Mexico City officials celebrated completion of the TBM with a cutterhead turning ceremony. The Mexico City Metro is one of the world’s largest, with over 200km (125 miles) of rail and nearly four million daily passengers.