The drainage system in one of the world’s most populous cities is not sufficient for the more than 20 million inhabitants. Mexico City was founded on what was once an island in the middle of a lake, and is sinking at a rate of 10 cm per year. Over the previous 30 years, the city’s critical drainage lines have lost their slope, resulting in a 40 per cent reduction in overall capacity.
Mexico’s National Water Commission (CONAGUA) launched a $US2.8 billion Water Sustainability Program in 2007 for bulk water supply, drainage and wastewater treatment for the period 2007-2012. Six tunnel boring machines (TBMs) will be used in the construction of the new Eastern Wastewater Tunnel (EWT) with a total length of more than 60 km at a depth of up to 200 m.
The line is divided into six lots. Mexican contractor Ingenieros Civiles Asociados is responsible for lots 1, 2 and 6 – to be bored using Herrenknecht earth pressure balance (EPB) machines. Carso Infraestructura y Construcción, S.A.B de C.V will employ Robbins EPB machines to bore lots 3, 4 and 5. Eastern Wastewater Tunnel The tunnel is to serve as an alternative drainage system in addition to the central tunnel. The new tunnel will have 24 inflow ducts at a depth of between 150 – 200 m. The EWT consists of six stretches with a total length of 63 km and a planned inner diameter of 7 m. The drainage capacity will be on average 150 cubic meters of water per second.
The Emisor Oriente wastewater duct, located in Mexico City, is the largest inner urban wastewater system being built in the world. Two of the world’s biggest TBM companies, Robbins and Herrenknecht, are going head to head to construct the line. Herrenknecht earth pressure balance shields
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Herrenknecht is providing three TBMs for this project in diameters of 8.7 and 8.89 m. The CEO of CONAGUA José Luis Luege Tamargo witnessed the completion of the first TBM in February this year.
“The Eastern Wastewater Tunnel is one of the most important water projects in the world if we consider the investment volume, the length of the tunnel and the technology used,” he said.
S-497 and S-498:
- Diameter: 8,700 mm each
- Installed power: 1,600 kW each
- Total thrust: 73,187 kN each
- Cutterhead torque: 9,772 kNm each
- Total weight: 905 tonne each
- Total length: 97 m each
- Tunnel length: 10 km, 8.8 km
S-519:
- Diameter: 8,890 mm
- Installed power: 2,080 kW
- Total thrust: 62,437 kN
- Cutterhead torque: 14,043 kNm
- Total weight: 867 tonne
- Total length: 84 m
- Tunnel length: 11.7 km.
Robbins is providing three 8.93 m diameter EPB machines. The Robbins EPB machines will bore lots 3, 4 and 5 of the Emisor Oriente project in geology ranging from sandy clay and gravel to tuff and pumice. The tunnel lengths will be 9.6 km, 9.7 km and 9.5 km respectively.
Mixed face cutterheads will be used on the machines, with interchangeable cutting tools depending on the ground conditions. In soil, the machines will utilise knife-edge bits, which can be changed out with 17 inch disc cutters in rock. For muck removal, the Robbins EPBs will feature 900 mm diameter ribbon-type screw conveyers to safely excavate ground with boulders, which are predicted to be up to 600 mm in diameter.
The three machines are slated for an early 2010 launch after design and assembly in the United States and China.
- Diameter: 8.93 m
- Installed power: 1,900 kW
- Cutterhead torque: 14,916 kNm
- Total length: 90 m back-up + 12 m EPB
- Tunnel length: 9.6 km, 9.7 km, 9.5 km.
“The project will significantly reduce the risk of flooding in Mexico City and it will improve the safety and well-being of the inhabitants and protect their properties,” said José Luis Luege Tamargo.
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