Shani Wallis, TunnelTalk

An EPBM of 9m diameter dominates the workshop. Beside it assembly of a second machine progresses and the components laid out on the factory floor await their building into a third machine of equal size.

EPBM fractory tests

The three machines are Robbins EPBMs ordered and heading to Mexico to excavate nearly 30km of the Emisor Oriente drainage project in Mexico City, a project that is reckoned to be the largest combined sewer and storm drainage tunnel project in construction in the world at the moment and perhaps of all time. The three Robbins TBMs will excavate almost half of the 62km long x 7m i.d. segmentally lined tunnel, another three EPBMs from Herrenknecht completing the other half.

The event in Corpus Christi, Texas on Tuesday and Wednesday of this week (February 2 and 3) celebrated assembly and factory testing of the first machine and arrival of further major components for TBMs two and three from the Robbins factory in China.

To the event Robbins invited members of the international trade press and leading members of the project owners the National Water Commission (Conagua), senior managers of the contractor Carso Infraestructura y Construcción, S.A.B de C.V. who have bought the machines, and an entourage of TV and newspaper journalists from Mexico City.

Robbins President Lok Home (left) and Director Luege of Conagua (right)....

"This is an extremely important and urgent project for us in Mexico City," said José Luis Luege Tamargo, Director of Conagua. "There are major drainage tunnel networks and canals in our metropolis of more than 20 million people, but these are now at maximum capacity. The Emisor Central system is particularly under stress. The city is founded on what was once an island in the middle of a lake. The city continues to sink as the soft material beneath continues to drain. As a result the city's critical drainage lines have lost their operating gradients and about 40% of their overall capacity. The Emisor Central system is now running under a high internal water pressure which runs the risk of bursting at the weakest points and causing city centre flooding of devastating proportion, similar in scale as the flooding of New Orleans initiated by Hurricane Katrina".

"Something needed to be done and our solution is this investment of about $US1.2 billion to build the 62km long x 9m diameter Emisor Oriente as a first class high capacity facility that will relieve the Emisor Central and provide and extra 150m³/sec to the city's sewerage and drainage systems," explained Luege. "These Robbins TBMs represent 50% of the mechanical tunnelling operation and we are pleased to see this first machine in operating mode, the second in assembly and all three looking robust, well designed and fit for conditions to be expected."

.......are joined by Carso managers to push the start button

Speaking at the event, Lok Home, President of Robbins, told TunnelTalk that this is a high profile order for the company. "An order for three big 9m machines represents about $52 million in turnover. That's a figure that used to be the company's annual turnover in years gone by."

"These three large EPB systems also confirm Robbins as a competitive manufacturer in the soft ground sector as well as a leader in the rock tunnelling sector," added Home. "The machines follow on from the EPBM that the Traylor/Shea JV used very successfully in Sacramento, achieving rates of 210m/week and 50m/day for recent breakthrough, and the EPB systems we have commissioned for the rail project in Guangdong, China; the Santo Domingo Metro in the Dominican Republic; and the 10.2m diameter machine in site assembly at the moment for Line 12 of the Metro in Mexico City."

"It is good that Mexico is once again investing in public infrastructure after many years of inactivity," said Home. "These machines and the TBM on the Metro follow on from the last time we had a project in Mexico with a Boretec machine to a large water supply tunnel project for Mexico City back in the 1980s."

First of three machines in assembly

Among those celebrating the accomplishment was a team from Wells Fargo Bank who helped fund manufacture of the machines. "This was a big order for us to underwrite, fund and guarantee all at once," said Jim Virost, CFO for Robbins. "It was made possible in large part by the Ex-Im Bank credit facility arranged by the Wells Fargo International team and extended by the US federal government's export/import financial institution. Ex-Im Bank also helped fund manufacture of the two 10m Robbins machines built for the AMR irrigation project in India and that effort won an award for excellence for export funding in the financial industry." Lynn Durning, Senior Vice President for a regional division of Wells Fargo explained that: "We help secure lines of credit for all kinds of businesses and working with a manufacturer of tunneling equipment has been particularly interesting. One of the stipulations with the Ex-Im Bank is that 51% of the work is carried out in the United States so assembly of the machines at this facility here in Corpus Christi from large steel components supplied from China and electronics and hydraulics sourced partly here in the US as well as Europe, complies with the rules."

Design of the machines
The three EPB systems are designed for demanding conditions. All three machines have mixed face cutterheads with back-loading interchangeable cutting tools the cutterhead of the first machine for Carso fitted with 17in disc cutters to drive predominantly through volcanic basalt, tuff and pumice while the second is fitted with a soft ground set of tungsten carbide knife-edge bits which can be changed out for disc cutters if necessary.

All three TBMs will work up to 150m below ground and under up to 10 bar ground water pressure. From the excavation chamber, muck passes into a long screw conveyor system designed to control the high pressures and allow muck to discharge at the end at atmospheric pressure. The first inclined section of the system to the guillotine gate and stone trap is a 900mm ribbon screw capable of handling boulders of up to 600mm (24in) in diameter.

All three machines have a vacuum segment erector

The remaining section of the conveyor across the top deck of the gantry of the trailing backup that will neutralize ground pressure is a central shaft auger screw. From the discharge muck will travel on a transfer conveyor back to a continuous conveyor system that will haul muck back through the tunnels and via vertical conveyors to the surface stockpiles for onward disposal. The haulage conveyors for the three TBMs are supplied also by The Robbins Company. This is an accompanying order of some $15 million and comprises more than 30km of belt conveyor equipment.

The machines are fitted also with vacuum segment erectors and a through-the-tail-skin grouting system for injection of a two-part annular grout system. An active articulation will allow for smooth tunneling through the many curves on the alignment. Curves of 2-3 degrees in each boring stroke can be accommodated without risk of ring deformation. The precast segments for the three TBM drives of more than 9.5km each are being cast at three yards established by the contractor Carso.

Carso managers and Director Luege with the assembled EPBM

The first gantry of each TBM is manufactured in the US from components supplied from China while the remaining gantries of the backups are being fabricated in Mexico City by Moldequipo S.A. de C.V., the company of Roberto Gonzales, which also represents Robbins in Mexico. Gonzales and members of his company and joined by Jack Chao, Managing Director of Robbins Asia Pacific Ltd, were also at the event in the workshops in Corpus Christi, a facility owned by and rented from Kiewit for the purpose.

The second two machines are scheduled to be assembled and factory tested by the end of March when all three will be disassembled and shipped by sea to Mexico. The conveyor systems are to be delivered overland in a fleet of more than 400 40-tonne trucks. Once into their strides the six EPBMs on the new Emisor Oriente are expected to complete all tunneling by 2012.

References

Robbins EPBMs to drive Mexico City drainage - TunnelTalk, Nov 2008
Tunnel with embedded liner holes through - TunnelTalk, Nov 2009
Robbins EPBM at work in Sacramento (video) - TunnelCast, Oct 2009
Robbins EPB to China's new Chengdu Metro - TunnelTalk, Oct 2009
Records tally for Robbins EPBs in Guangzhou - TunnelTalk, Aug 2009
Onsite assembly in Mexico for Robbins EPBM - TunnelTalk, Jan 2010
Other EPBMs on the Emisor Oriente project in Mexico City - TunnelTalk, Feb 2009

CONAGUA Mexico's National Water Commission
The Robbins Company

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