In the past decades, more water has been exploited from the underground than it could regain from rainfall. The consequence: The metropolis of 20 million has sunk up to twelve meters in some quarters. The sewage system has lost most of its efficiency due to the lost gradient and frequent floddings are the result. The new sewage collector "Tùnel Emisor Oriente" with an inner diameter of seven meters will be able to divert up to 150m3 of sewage per second. Additionally, the city plans to reduce the sinking of the city with an intelligent groundwater management system.
It is the world's largest sewage project. The tunnel will have 24 inflow ducts at a depth of between 150 meters and 200 meters. The East Sewage Tunnel consists of six stretches with a total length of 63 kilometers.
Herrenknecht delivered three large-diameter Earth Pressure Balance Shields for the “Emisor Oriente” project and these will excavate more than 33 kilometers of the gigantic sewage system. In mid-February 2009, the first of the three machines was presented to the Mexican project managers in the Schwanau plant ready for handover.
The launch shaft for the Herrenknecht EPB Shield S-497 was tight - 16 meters in diameter only. The TBM's modular concept was the solution. The gantries were connected to the machine piece by piece after the machine had started tunnelling. A belt conveyor from the Herrenknecht subsidiary H+E Logistik transports the muck on the three EPB Shields that are operated precisely with a navigation systems made by the Herrenknecht subsidiary VMT. Transport of material and personnel is handeled by rolling stock from the Herrenknecht subsidiary MSD.
In March 2019 the last Herrenknecht EPB Shield gets close to the final breakthrough. It tunnelled through heterogeneous ground, with layers of hardrock and with high groundwater pressure. Completition of "Emisor Oriente" is planned in time for the start of the rainy season in the summer of 2019.