• Two tunnel workers climb through the cutter head on May 13, 2011, to celebrate the safe completion of mining the 10.2 kilometre Niagara Tunnel

    Two tunnel workers climb through the cutter head on May 13, 2011, to celebrate the safe completion of mining the 10.2 kilometre Niagara Tunnel. (Photo courtesy of Ontario Power Generation)

The Niagara Tunnel route follows the same path as two tunnels built in the 1950s, but at a much greater depth (Map: Chris Brackley/Canadian Geographic)

“How is it down there?” asks Dalton McGuinty.

“It’s dark,” comes the disembodied reply. The crowd titters. We’re assembled in a massive tent alongside the Niagara River — power-brokers in suits, construction workers in battered, decal-covered hard hats, untucked journalists in khakis — to witness the final “breakthrough.”

After a five-year battle with the fickle subterranean forces of the Niagara Escarpment, the long-awaited mega-tunnel under Niagara Falls is 99.99 percent complete. Just a metre and a half of solid rock remains, and the Ontario Premier is preparing to radio the “dig” signal to equipment foreman Kevin Collins, far underground in the control room of the world’s largest hard-rock tunnel boring machine.

A succession of speakers in the preceding hour had laid out the epic scale of the project: a $1.6 billion, 10.2-kilometre-long tunnel that has displaced enough rock to fill 100,000 dump trucks. It will ultimately funnel water from its intake above the falls to the Sir Adam Beck Generating Stations downstream at a rate that would fill an Olympicsized swimming pool every five seconds, spinning turbines to power 160,000 Ontario homes — a key plank in the province’s shift from fossil fuels to sustainable power. Urbanization long ago gobbled up the land alongside the Niagara River, making a canal impossible and the disruption of conventional drill-and-blast tunnelling a non-starter. So Ontario Power Generation (OPG) was forced to go deep. It commissioned the unprecedented boring machine, a wormlike behemoth that could chew through rock without waking the honeymooners slumbering above it, and, since tunnelling machines, like ships, are always female, dubbed her “Big Becky.”

Planning for the tunnel began in 1982. In the years that followed, routes were proposed, cores were drilled, rock samples were studied, impacts were assessed. Tunnelling finally started in 2006, but a trip underground is still a voyage into the unknown. “No matter how many investigations you do or how much money you spend up front, there’s always a certain uncertainty left,” says Ernst Gschnitzer, the project manager for Austrian construction giant Strabag, which is in charge of designing and building the tunnel. Sure enough, the carefully laid plans of an army of engineers began to unravel as soon as the tunnellers reached a troublesome layer called the Queenston shale, and as months passed and losses mounted, it began to look like yet another victory for geology in the age-old battle of man versus rock.

If you join the crowds strolling beside the Niagara River on a summer’s day and head upstream from Horseshoe Falls, you’ll pass a series of stately stone buildings fronted by majestic arches and columns: Canadian Niagara Power; Electrical Development Company; Ontario Power Company. All are now empty, vestiges of a long history that dates back to 1758, when Frenchman Daniel-Marie Chabert de Joncaire de Clausonne first harnessed the waters for his sawmill just above the American Falls.

Not surprisingly, the seemingly limitless torrent of the falls has played a central role in the history of hydro power and of electricity itself. One of the first hydroelectric generators in the world began powering 16 street lamps on the New York side of the river in 1881. A decade and a half later, when the Niagara Falls Power Company chose Nikola Tesla’s alternating-current (AC) transmission scheme for sending power to Buffalo instead of Thomas Edison’s direct-current (DC) scheme, the “War of the Currents” effectively ended and the template was established for how we transmit and use electricity to this day.

The current Sir Adam Beck Generating Stations are angular, modern structures jutting into the river about eight kilometres downstream from the falls, far from the cluster of old generating stations that proliferated above the falls at the start of the 20th century. That’s also where the Niagara Tunnel resurfaces, and it’s in a prefab office on the construction site there that I meet with Rick Everdell in August 2010 — nine months before the breakthrough ceremony — for my first tour of the then incomplete tunnel. Everdell, OPG’s project director for the tunnel, is a cheerful 59-year-old engineer who’s the last remaining member of the original team that started working on the project in 1982.

“We got smarter as time went on,” says Everdell, explaining the downstream location of the current power plant, which started operation in 1922. While the earlier plants harnessed the 55-metre drop over Horseshoe Falls, water for the first Beck plant was channelled through a canal that ran alongside the river but stayed on top of the Niagara Escarpment. When it finally reached the turbines 10 kilometres away, the water dropped 89 metres before rejoining the river — almost the entire height difference between Lake Erie and Lake Ontario, putting to use energy that was otherwise squandered in the rapids below the falls.

The next major step came in the 1950s, when the Sir Adam Beck II Generation Station added 16 more generators to the original 10. To feed the new station, the provincial utility dug two tunnels, starting above the falls using drill-and-blast construction, a disruptive approach that required five major construction shafts to be sunk along the route in the city of Niagara Falls. The tunnels ran only as far as St. David’s Buried Gorge, an ancient river valley that crosses the modern Niagara River a few kilometres below the Falls. Since the loose silt filling the gorge couldn’t be safely tunnelled through, the tunnels have to veer back up to the surface and the water completes its journey in a canal. The Americans, meanwhile, were also building tunnels to feed a new power plant across the river from the Beck stations, using the even more disruptive cut-and-cover technique, essentially digging a giant trench then covering it.

These days, as much as 4,000 cubic metres of water per second are diverted through various tunnels and canals around the falls to generate electricity. Canada and the United States signed a treaty in 1950 agreeing to ensure that at least 2,832 cubic metres per second flows over the falls between dawn and dusk during the tourist season from April to October. At other times, the minimum is cut in half, to 1,416 cubic metres per second. “The result is that the scenic flow requirement uses about one-third of the average Niagara River flow,” says Everdell. The rest is available for power generation, split 50-50 between the two countries.

The earliest hydroelectric systems in the area, which failed to capitalize on the full potential of the falls’ drop, were “repulsive to the engineer, because of the great waste,” wrote the renowned Scottish engineer George Forbes in 1895. In a similar vein, Everdell shows me a graph called a “flow-duration curve,” based on eight decades of river data. It reveals that Canada’s share of the water available for power exceeds the maximum capacity of the existing canal and tunnels about 65 percent of the time. “With the new tunnel in place, we’ll reduce that to about 15 percent of the time,” he says with evident satisfaction, “so there’s really not a whole lot of energy left in that water.”

The original plan, drawn up three decades ago, called for two new tunnels and a new underground generating station. Geotechnical studies started in 1988, and environmental approval for the full project was granted in 1998. But the current plan has been scaled back to only one tunnel and no additional generating capacity. “Essentially, what we’re doing is providing more fuel to the existing generating stations,” says Everdell. “That’s where you get the biggest bang for your buck.” The Ontario government finally gave the go-ahead in 2004; the billion-dollar design-build contract was awarded to Strabag in 2005; Big Becky was built from scratch in 12 months, and began tunnelling in September 2006. And then the trouble started.

The new tunnel will provide additional water to Ontario Power Generation’s Sir Adam Beck generating stations to produce additional clean renewable energy for Ontario — on average, about 1.6 billion kilowatt hours per year. (Photo courtesy of Ontario Power Generation)

Rick Cheel is an outcrop guy. The sedimentologist at Brock University in St. Catharines, Ont., likes to stand back from an exposed chunk of, say, the Niagara Escarpment and see how the layers of rock get thicker and thinner and change their composition and colour across the rock face. He’d rather be out in the field than in a lab. “Looking at core samples,” he says with distaste, “is like walking up to a great view with two Funk & Wagnalls dictionaries, clamping them onto the rock face and looking only at the rock between those two books — and being blind to everything else.”

Still, shortly after starting at Brock in the late 1980s, Cheel gladly signed on to help analyze core samples for a local company doing early preparatory work for the Niagara Tunnel. The company had drilled holes to get rock samples, cut them into tiny rectangles, glued them to glass slides and then ground them down until the rock was almost transparent so that it could be analyzed under a microscope. Cheel’s job, for $50 a slide, was to count how much mud, quartz sand and calcite appeared in each sample; the company then used the data to estimate a cost per metre for drilling through the rock.

The layer Cheel was analyzing was called the Queenston shale, a remnant of the vast inland sea that once covered southern Ontario. Rivers flowing down the proto-Appalachian mountain range deposited layers of mud along the shoreline, producing a stratum of crumbly rock tinted red by iron oxide and containing about 60 percent clay — perfect, it turns out, for making bricks. Then, starting about 430 million years ago, the sea level dropped, rose and dropped again repeatedly, producing a series of rock layers topped by the Lockport Dolomite, a relatively resistant formation made up of cemented fragments of broken up shell material deposited in shallow estuaries along the shoreline of the inland sea.

The Niagara Tunnel route follows essentially the same path as the two 1950s tunnels, but at a much greater depth. While the old tunnels rise to the surface from depths of 45 and 60 metres right before St. David’s Buried Gorge, the new one dives to a depth of 160 metres to go underneath the gorge — and that takes it into the Queenston shale. Core samples drilled long after Cheel’s work was finished revealed that the pores in the shale were saturated with salt water; therefore, any contact with fresh water would cause the rock to gradually swell, a finding that meant the tunnel would have to be lined with a 100 percent waterproof membrane. Other than that, the shale looked diggable, at least from the tightly constrained perspective of the core samples.

The assumption sedimentologists typically make when they dig core samples is that the rock between the cores will be the same as it is in the cores. “But,” says Cheel, “you never know.

The fact that we can even contemplate a tunnelling project on this scale is a triumph of engineering persistence that dates back to 1818, when Marc Brunel patented the tunnelling shield he would use to dig his famous tunnel under the River Thames in London. The design was inspired by shipworms, which secrete a chalklike substance to line the passages they create while boring through a ship’s timbers. Brunel’s cast-iron shield protected a grid of 36 miners from the rock above them as they dug forward 15 centimetres at a time, then paused to line the newly exposed rock with concrete and to jack the tunnelling shield forward. It took 18 years to inch a tunnel under the Thames at an impractically slow pace, but the basic principle is still in use today.

Over the next century, a steady stream of prominent engineers came up with grandiose schemes for massive tunnelling machines that would replace feeble human power with mechanical muscle. Several were built, but all ended in failure, often within the first few metres of the planned project. The problem was finally cracked by a mining engineer named James Robbins, who came up with the idea to mount a collection of rapidly spinning “cutter disks” on a giant circular “cutter head” that rotates a few times a minute. Pressing into the rock with several tons of pressure, the cutter disks fracture the rock and score concentric circles into the rock face as they rotate. Robbins deployed the first hard-rock boring machine to cut through the limestone for Toronto’s Humber River sewage tunnel in 1956. Since then, the Ohio-based Robbins Company has built boring machines for every conceivable terrain and location — through the Alps and the Andes, above the Arctic Circle, beneath the English Channel — culminating in the biggest ever built, Big Becky.

The problem with the Queenston shale, it turns out, is that it’s too soft — an unworthy adversary for Big Becky’s 35 tonnes of forward pressure. The thin layers of flaky shale are also subject to powerful horizontal stresses, so instead of forming a nice arch above the boring machine,the shale simply crumbles on top of the machine before the usual ceiling support (rock bolts, metal ribs and mesh) can be installed. As much as three to four metres of “overbreak” at a time tumble down, creating chaos that added $600 million to the project’s cost and three years to the timeline. Water is now expected to begin flowing through the tunnel in December 2013.

As Rick Everdell explains the problems to me, I can’t help glancing nervously at the self-breathing oxygen units that Mike Zegarac, a veteran tunneller with a hard hat and a no-nonsense demeanour, has just piled on the table. We’re in a conference room in the construction-site office a few kilometres away from the tunnel’s outlet, getting a safety briefing before heading down into the depths. The tunnel also has a 25-person refuge chamber of the type made famous by the Chilean miners who spent 69 days trapped underground in 2010. It’s situated just behind Big Becky, but the prospect of using it doesn’t sound very appealing. The two men are quick to reassure me: the overbreak problem has been addressed by making significant modifications to the tunnelling process and to the tunnelling machine itself, such as drilling “umbrella” pipes into the rock above the advancing machine to keep the rock stable. And no workers, or visitors, are allowed to work under unsupported rock. “They do nothing above their heads,” says Zegarac. “Everything is in front of them.”

With that reassurance, I head outside and hop into a mud-splattered pick-up truck. We drive alongside the long, low piles of shale that have already been extracted from the tunnel, some of which will be used by Hamiltonbased Century Brick Ltd., and past the treatment plant where water pumped out of the tunnel is cleaned up before being discharged into the river. Finally, the road slopes down like the entrance to a gargantuan underground parking garage, toward a massive 14.3-metre circular opening permanently shrouded in mist, thanks to the moist, cool underground air. I know the stats — within that opening, you could easily stack three eighteen-wheelers on top of one another and have room to spare — but this hits home only when I get out and stand in front of it.

The 14.4-metre diameter tunnel, as it looks before the permanent concrete liner is in place. When complete, all the pipes, tubes, lighting and cables will be removed leaving a smooth concrete surface. (Photo courtesy of Ontario Power Generation)

The 35-minute drive to the end of the tunnel is like a time-lapse video of the construction in reverse. At the outlet, the tunnel is essentially complete: a full concrete lining covers a waterproof membrane in a perfectly circular shape. (The circular cross-section means, among other things, that the cement trucks driving in the tunnel need split axles. They also need to be able to drive in both directions, since three-point turns aren’t an option.) About 300 metres into the tunnel, we pass workers installing the upper two-thirds of the concrete lining; two kilometres in, they’re installing rock bolts and wire mesh then spraying on shotcrete to fill in the spots where the ceiling has crumbled; five kilometres in, they’re laying down the lower third of the concrete lining. For the rest of the drive, we bump and weave over pothole-riddled clay. Finally, the bright lights of Big Becky herself appear in the distance; we park the truck at a rakish angle partway up the side wall of the tunnel and continue on foot.

At this point, we’re just a few hundred metres from the mist and thunder of the greatest chute on Earth and the equivalent of 29 storeys almost directly below Canada’s tallest hotel, the 53-storey Niagara Falls Hilton. But instead of slipping into a room with a view and a mini-bar, I prepare to enter a 150-metre-long, 4,000-tonne machine whose metal parts are so covered in grime and corroded by the salt oozing from the walls that they look like relics from a century-old coal pit. Zegarac points to the semicircle of rough sandstone arching just above our heads. “Where we’re standing,” he grins, “was solid rock yesterday.”

A few minutes after my arrival, a siren sounds to warn that drilling is about to restart after a maintenance shutdown. The whole structure — a four-storey maze of ladders and platforms that feels, appropriately enough, like the engine room of a submarine — begins shaking. A minute later, a higher-pitched siren sounds and the shaking escalates to a soul-rattling rumble that makes balance and coherent thought difficult. Behind a screen in front of me, 85 disk cutters begin spinning, while the entire front end of the machine slowly rotates, carving concentric circles into the rock. To my left, a stream of dirt and fist-sized rocks starts tumbling along a high-speed conveyor belt that runs from the cutter head all the way back to the tunnel’s exit.

The rock around us is greenish rather than red; after dipping under St. David’s Buried Gorge, the tunnel veered upward to escape the crumbling Queenston shale. Now in the Grimsby sandstone, Big Becky is averaging close to 20 metres of tunnelling a day, a vast improvement over the top speed of 13 centimetres a day during the worst of the overbreak problems.

A crew of 20 is deployed at various points around the machine — some in the control room, others preparing the metal ribs and mesh that will be bolted to the newly exposed sections of rock ceiling, while a few more weld parts together in a shower of sparks. The tunnelling crew, part of a total workforce that peaked at 580, is split into two shifts to keep Big Becky running 20 hours a day, with four hours for daily maintenance. Working underground isn’t for everyone; many who try it last less than six months. But those who stay often spend the rest of their lives as tunnellers, moving from project to project.

Zegarac is one of the lifers. Originally from Belgrade, he’s spent 37 years working in tunnels, first in the former Yugoslavia, then in Romania, Libya and across North America: Vancouver; Austin; Detroit; Cleveland; and a half-dozen projects in Ontario, including the St. Clair River tunnel between Sarnia and Port Huron, Michigan. He leans toward me and yells something in my ear over the din, pointing at the rock wall beside us, which doesn’t seem to be doing much of anything. He turns away to speak to one of the workers and then, a minute later, turns back and points at the wall again with a triumphant air. Sure enough, the wall — and the entire bowels of the Earth, as far as I can tell — has moved backward by about two centimetres.

After watching the mining for half an hour, we retreat toward the truck, the powerful vibrations fading as we move away from the cutters. When we step out the back of Big Becky, Zegarac pauses and says simply, “Look up.” I do, and my sense of scale comes rushing back. It’s really, really big. It’s an engineering feat of immense proportions, and yet it’s completely invisible to the tourists relaxing in the Hilton directly above us — and once it’s finished, it will remain invisible for the century or more of its service life as it delivers fuel to generate 1.6 billion kilowatt hours per year. Standing in the darkness, I feel as though I’ve been granted a temporary membership into the secret global fraternity of tunnellers.

This is the feeling I remember, nine months later, as I stand blinking in the bright sun waiting for Dalton McGuinty to give the signal to start up Big Becky for the last time. McGuinty has just delivered a fiery speech about the need to rebuild Ontario’s energy infrastructure — a task that, like the tunnel itself, will be technically challenging, time-consuming and expensive. It’s worthwhile, says the Premier, because we’re doing it for our children and grandchildren. That’s the theme he returns to now, as he quizzes Kevin Collins, down in Big Becky’s control room, via radio link.

“Have you got a family?” asks McGuinty.

“I do,” comes the reply. “I’ve got a wife and three kids.”

“How old are the kids?”

“Six months, two and five.”

“Why do you work so hard every day?”

There’s a pause, and an expectant hush falls over the assembled dignitaries. Grand forces of politics, engineering and economics are all converging in this moment of triumph, as one of the greatest mechanical marvels ever built prepares to punch through its final barrier. But Collins’ answer is as inevitable as it is unexpected.

“It’s fun down here in the hole!”