February 1, 2014 by David Godkin
Most blame politics for Albert Mathieu’s failure to realize his dream, a tunnel underneath the English Channel. Curiously, no one questioned the 19th century French engineer’s proposed method: horse-drawn coaches, illuminated by oil lamps as far as an artificial island mid-Channel where the horses would be changed and work resumed until their arrival in Calais, France. Two hundred years later, tunnel builders are a whole lot more successful working underground, in large part because of their methods and machines.
We call her “Big Becky”
By 1994 “the Chunnel” was an accomplished fact, using six open-faced tunnel boring machines (TBMs) at Shakespeare Cliff near Dover and on the French side with six earth pressure balance TBMs named in characteristically French fashion after women: Brigitte, Europa, Catherine, Virginie, Pascaline and Séverine. But TBM designers tell us we have reason to be entranced by the “iron ladies” here in North America, too. One of the biggest, says Lok Home, president and Principal owner of The Robbins Company in Solon, Ohio is “Big Becky,” at one point the world’s largest hard rock TBM.
“Most tunneling in rock is done by drilling and blasting because it’s generally much cheaper per meter of excavation. In long tunnels, anything over five kilometres the world uses tunnel boring machines. And Big Becky is one of the best.”
At just over 10 kms in length, the hydroelectric tunnel under the City of Niagara Falls, Ontario and completed just this past year needed a TBM with enough oomph to help clear about 1.6 million cubic meters of rock and debris. Operating as deep as 140 meters and powered by 15 electric motors generating 4.7 megawatts or 6,375 horsepower Big Becky would go on to bore a tunnel 14.4 metres in diameter—as wide as some flatbed trucks are long.
Certainly the politicians were impressed. They called it “an engineering feat” helping to feed an additional 150 megawatts to the city’s aging generating station, or enough to power 160,000 homes. But that didn’t mean it was easy. Comprised mainly of sedimentary rock, Niagara’s geology generated much discussion among the owners and designers about the best kind of TBM to use: a TBM that has no shield and leaves the area behind the cutter head open for rock support, or a closed TBM that erects concrete segments to support unstable tunnel walls behind the machine as it cuts.
They ultimately decided on an open-type or main beam TBM, relying on the self-supporting properties of the geology itself. Why this decision was controversial, says Home, became apparent when weak rock at the top of the very wide diameter tunnel began caving in. “The cutter head as it was cutting was ingesting more rock breaking out immediately above it.” Not that this was the TBM’s fault, Home stresses. “The TBM actually set some records and did really well in the project.” The subsequent charge order, everyone agreed, occurred because they’d “missed the fact that this rock wouldn’t self-support.”
So, instead of redesigning “Big Becky,” contractor Hatch Mott MacDonald focussed on redesigning the rock support mechanism at Niagara, e.g. changing the scaling system and work platforms. They also changed the depth at which the TBM would work, reversing the project’s “unique” decision, says Home, to “bore down deep to get under the old Niagara Gorge which was there before the last glaciation” and “bore up into the formation that did self-support.”
Once complete, the tunnel was fitted with an impervious membrane and a concrete lining, pre-stressed by high-pressure grouting. Theoretically, what you’re trying to do by lining the tunnel in this way, is to return the geology in which the tunnel sits to a state as close to the one that existed prior to the boring, explains Home. Thus, if there’s a water buildup it will circumvent the tunnel with the lining absorbing the pressure and other stresses.
The Robbins Company in the 1950s, Home stoutly proclaims “manufactured the first successful tunnel boring machine,” defining success in conventional terms as completion of project on time and on budget. It is not defined, Home emphasizes, by the complete absence of equipment break down. In tunnel building “machines are always going to break down,” he says, particularly when cutting through hard rock.
“These are highly complex machines and even today it would be highly unusual if you didn’t have some break downs over several miles. These include minor breakdowns like valves, or major breakdowns like main bearings.”
That bearing’s got to be bullet proof
Following its much talked about takeover of TBM manufacturer Lovat Inc. in April 2008, Caterpillar would phase out its TBM group by mid-2014. Cat made the decision last year, said group president Stu Levenick, because “the tunneling business no longer fits” Caterpillar’s “long-term strategy.” Gary Benner general manager for Technicore Underground Inc. in Toronto, suggests there might have been another reason for the closure. “I think they’re finding that the tunnel business is not like other businesses.”
“When you’re in equipment supply you’re talking about loaders and backhoes and when one breaks you simply bring in another one. But when a TBM breaks it’s underground and you have to design in them the ability to repair them underground.”
Motors are easily replaced underground and the hydraulics easily repaired. All the cutting teeth are designed to be replaced as you go, too. Benner’s biggest concern while tunneling is the TBM’s main bearing. “If that goes, you’ve got to extract the machine.” It’s for this reason that TBM’s are rarely off-the-shelf designs, but instead are designed for a specific project. A case in point: Ontario’s 10-year Hydro One project.
“It has a ridiculously tight corner on it, so we designed the TBM with double articulation so it could get around this corner. It’s not something you would do normally and has never been done before that we know about.”
Another job getting a lot of mainstream ink in Ontario is excavation of soil and rock beneath the Western Gap, a 400-foot channel in Lake Ontario separating Billy Bishop Toronto City Airport from the mainland. A 660-foot pedestrian tunnel the size of a truck tunnel, the Billy Bishop features a 100 foot elevator and moving walkways at one end and a steep bank of escalators at the other. The biggest impediment, says Benner is not all that Lake Ontario water sitting above the heads of the crew; nor is it the surrounding geology. “Our biggest challenge really is getting down through the man-made stuff, wooden piles and old sheet piling.”
Hydraulic breakers and grinders enabled Benner’s crews to eventually hit more manageable solid rock. But the really unique part of the job, says Benner, was drilling seven tunnels all interlocked and filled with concrete to create an arch that would provide the Toronto Port Authority assurance the roof of the tunnel bored from below would remain stable. From there, two Canadian-made tunnel boring machines “Chip and Dale” —nicknamed
after the famous Disney chipmunks—took over.
Weighing 90 tonnes and worth $2million apiece the TBMs measure 6.5 feet in diameter and 36 feet in length, excavating at a rate of 39 to 49 feet per work day once it’s jacked into the ground. “To advance, the TBM uses a gripper system that pushes against the side walls of the tunnel using the friction of the gripper to allow the machine to go forward,” Benner explains. Retraction of the propel cylinders at the end of a stroke repositions the gripper assembly for the next boring cycle. The grippers are then extended, rear legs lifted and boring resumed.
All tunnels are not created equal
“Not every tunnel has to go under a mountain. If you want to cross a major highway with a large diameter concrete storm line we’re the guys you get.”
Firms like Underground Consulting do a great job on major tunneling projects such as the Billy Bishop airport, but on some jobs, says Calgary Tunneling project coordinator Alan Cluett, you have to think small. And that can mean very small, using an unmanned, remote controlled micro tunneling machine (MTBM) to install pipe in ground conditions below a water table. Or you install a larger pipe jacking system like the one Cluett’s company Calgary Tunnelling used to build a water runoff system at the Calgary International Airport Runway Development Project.
“We’ve done a crazy amount of work there putting some large diameter 2400 mm concrete pipe and some 2100 mm concrete under the road and the fuel lines. Because of those diameters we needed an Akkerman TBM for that.”
To bore both tunnels Cluett’s crews relied on Akkerman’s 5000 Series, a complete, all-in-one pipe jacking system containing TBM, hydraulic power unit, skid base sections and a thrust yoke. It also features a pumping unit with two independent hydraulic systems, one to supple oil to jacking cylinders and anther supplying oil to the TBM and conveyor circuits. A manned machine, the TBM’s drum roller and conveyor are activated using stick controls with the driver checking its position at the end of each cycle against a laser beamed from the front of the tunnel.
“He checks his point to see where he’s at and then makes small adjustments to articulate the head in whatever direction he wants to go.”
While there are many variables, Cluett estimates a TBM will, under decent soil conditions, cut through 12 to 20 metres in a day. Every bit as important as the TBM to cut through clay, he says, are the backup systems used to cart it away. That’s because the operator can see the clay fall onto the conveyor but has no control over it once it is transferred into the bucket or haul carts for removal. That job falls to the train operator.
“When the bucket is close to being full he’ll give a signal so that the operator knows to stop the drilling, shut the conveyor belt off so that the train operator can drive the train out and can be emptied.”
TBMs of this size won’t get you through every soil condition and that’s especially so in Calgary where soil conditions vary from wet, runny sand to dense clay to hard rock – all in a single stretch of airport runway. “Look at your desk and imagine that’s a rock. When you get to that kind of material you can’t bore through it. You drill and blast.” TBMs still the way to go, though? You bet, says Cluett. Assuming they’re approved, environmental concerns around the Keystone and Northern Gateway pipelines will make TBMs and their much smaller footprint a necessary part of the construction equation.
“There will be a lot of streets and a lot of roads. That means a lot of crossings and a lot of TBM work.”
David Godkin is a B.C.-based freelance writer and regular contributor to On-Site. Send comments to email@example.com.