A Robbins Crossover tunnel boring machine (TBM) has been launched on the Túnel Emisor Poniente II (TEP II) waste water project in Mexico City, Mexico. The 8.7 m diameter machine is the first dual mode TBM by Robbins, capable of operating in rock and earth pressure balance (EPB) mode for soft ground, commissioned by the company in North America.

A consortium comprising Aldesa, Proacon and Recsa will excavate the 5.9 km tunnel through volcanic rock, sands and clays. As well as being able to work in these ground conditions, the TBM was delivered through Robbins’ Onsite First Time Assembly (OFTA) service, which cuts down delivery time, as the TBM is not assembled at a factory prior to being broken-down for shipping.

The contractor at TEP II is confident about the machine’s abilities, which are optimised for hard rock but with many EPB characteristics. “In my opinion, the best part about the design of this TBM is the cutterhead; it is very robust,” said Sebastián Gallego Murillo, TEP II Production Manager for Proacon. He added that the biggest challenge would come near the end of the tunnel drive. “We expect to convert [from hard rock] to EPB mode due to the soils in this area. We will need to change out the cutters and modify the cutterhead.”

Regarding the project itself, Mr Gallego said, “This tunnel will reduce flooding in the west and northwest areas of the Valley of Mexico, and increase wastewater capacity. It will benefit three municipalities that are home to 2.1 million people.

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