Commissioning of the 8.93 m diameter tunnel boring machine (TBM) was fast-tracked for work on Lot 1 after flooding problems delayed another machine by six months.

Three Robbins TBMs and three Herrenknecht TBMs are planned for the massive wastewater line.

Lot 1 contractor Ingenieros Civiles Asociados Site Manager David Juarez said in order to compensate for time lost due to flooding, boring began with the Robbins machine at shaft 5 of Lot 1.

The Lot 1 site, located in the Ecatepec area outside of downtown Mexico City, has seen widespread flooding during each rainy season.

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The Gran Canal, an open sewer commissioned in 1910, is the area’s main sewer line and floods its banks regularly, causing road closures and significant health problems to those living nearby.

Due to a loss of slope because of the city’s sinking lake clays, the canal now has a positive vertical alignment below Mexico City – the portion of the canal outside the city has not been affected.

Increased volumes of water have the potential to overload current pumping stations and send the untreated water back into the city.

The Emisor Oriente project is designed to prevent flooding and increase the city’s wastewater capacity by approximately 150 cubic metres of water per second.

National Water Commission’s (CONAGUA) General Supply Coordinator for Potable Water Miguel Guevara said a treatment plant and a pumping station was currently being built to pump the water diverted into Emisor Oriente back into the Gran Canal where the slope has not been affected.

The Robbins TBM has started excavation at Lot 1, using umbilical cables connected to the surface and a sludge pump for muck removal.

Once it has bored 150 m, a Robbins continuous conveyor system and vertical belt will be installed for the remainder of the drive in mainly lake clays and sand.

Once the machine reaches the end of its 5 km drive to shaft 3A at Lot 1, it will be removed and readied for its original 8.6 km long bore at Lot 5.

Two more Robbins EPBs are scheduled for launch later in 2011 – 9.2 km and 10.2 km bores at Lots 3 and 4 respectively.

It will operate in parallel with the city’s other main wastewater line, Emisor Central. Since the central line was built in 1964, Mexico City’s population has more than doubled, straining the system’s capacity.

CONAGUA has said it hopes the Emisor Oriente will ease many of the city’s wastewater problems when opened.

“We are working hard on pieces of the problem, but the problem is not solved yet,” Mr Guevara said.

The project is due for completion in 2014.