It will take three years to drill a 10.4–kilometre tunnel under the city of Niagara Falls to divert more water to the Beck generating station. ZOE CORMIER details how it will be done
The city that boasts North America’s most powerful waterfall will soon be sitting on top of a massive hole created by the world’s most powerful hard–rock boring machine.
Using a drill with a diameter of 14.4 metres‚ Austrian construction contractor Strabag will begin digging a tunnel this summer to divert water from the Niagara River to the Sir Adam Beck Complex. The tunnel will run 10.4 kilometres‚ about 100 metres beneath the city of Niagara Falls.
The tunnel–boring machine (TBM) will be assembled from a number of pieces made by different manufacturers from around the world. Ontario Power Generation expects the assembly to begin by the middle of next month‚ and hopes that the tunnelling will get going as early as late July.
The TBM will drill through the rock seven days a week (excluding routine maintenance checks) for up to three years. Its final destination is the banks of the Niagara River‚ where a temporary dam will prevent the tunnel from being flooded prematurely.
The diameter of the tunnel‚ once beams and concrete are put in place to support the walls‚ will be about 12.7 metres.
The largest tunnels in the world made with boring machines are only slightly bigger –– a pair of 15.2–metre drills were used to complete two tunnels for roads in Madrid last year –– but the city of Niagara Falls sits on top of tough Queenston shale‚ while the Spanish tunnels were gouged through gravel and sand. The harder the rock‚ the more difficult it is to drill a wide tunnel.
Other larger hard–rock tunnels exist‚ including two that already divert water from the Niagara River to the Beck station. But they were created in the 1950s using the “drill and blast” method‚ which involves blasting rock out with explosives and then smoothing out the sides with concrete to create a round tunnel –– an extremely labour–intensive process.
The new tunnel will be made with the safer‚ more sophisticated method of slowly grinding away the rock with a circular drill‚ leaving a round tunnel that can be quickly and easily lined with support structures while the boring machine continues to move forward.
“In an urban area now‚ it is a bit more complicated than it was in the 1950s to perform drill and blast construction‚” says Rick Eberdell‚ Ontario Power Generation’s project director for the Niagara tunnel. Underneath the city runs a maze of sewers and pipelines that makes the use of explosives risky.
The tunnel‚ which will deliver about 500 cubic metres of water per second‚ is expected to boost the amount of “clean‚ renewable‚ low–cost energy you can get from the Beck station by 14 per cent‚ about 1.6 terawatt–hours” a year‚ OPG spokesman John Earl says. That’s enough energy for about 160‚000 homes.
“To put it in context‚” Mr. Earl says‚ “the province of Ontario last year used about 150 terawatt–hours. So 1.6 terawatt–hours is a small percentage over all‚ but for just one plant‚ it is a considerable addition.”
It was 100 years ago that the Ontario government brought power transmission under public control‚ distributing Niagara Falls energy to various parts of the province.
The construction of the tunnel is expected to cost close to $1–billion. The TBM alone will be about $30–million.
The drill was designed by Ohio–based Robbins Company‚ which has been commissioned to make more than 250 drills for 700 tunnel projects‚ including sewers‚ hydroelectric projects‚ highways and the English Channel Tunnel.
The drills used to create the Chunnel (11 in total‚ of which Robbins made five) were a mere 8.7 metres in diameter.
“This is way bigger than anything we’ve ever done‚” senior project engineer Richard Johnson says. “The largest before that we did was about 10 metres in diameter.”
The Niagara drill will be so big that it will contain a five–by–three–metre operating cabin‚ conveyor belts‚ cranes and staircases‚ roads for trucks‚ a rescue chamber in case of emergency –– even a lunch room.
“It’s going to be just massive‚” Robbins project manager Mike Kolenich says. The drill will weigh about 2.6 million kilos.
“The size of the machine is almost equivalent to a five–storey building‚” Mr. Kolenich says. “There will be ladders and staircases everywhere‚ so when you’re on top of the machine‚ if you were to look over‚ you literally couldn’t see the bottom of the tunnel because of all the equipment. You’ll be able to drive a truck underneath the machine up to the front end to load and unload materials.”
The front of the drill will hold a 14.4–metre circular “cutting head‚” studded with 85 half–metre blades that will fracture the rock. “As the cutter head rotates –– up to five rotations per minute –– the cutter discs roll around the rock as the machine thrusts forward.
The cutters score the rock similar to cutting glass.
“If you were to look at the rock face after the machine had completed a couple of revolutions‚ it would look like a giant target made up of concentric circles. The space in between the cutter paths is where it starts to fracture‚” Mr. Kolenich says.
The wear and tear from grinding the shale means that one or two cutter discs will have to be replaced every day.
The drill will crawl metre by metre until it has chewed through 10 kilometres of rock.
Four “shoes‚” 10–metre long steel pads‚ will push out against the sides of the tunnel while four steel cylinders thrust the 400‚000–kilogram cutting head ahead as it rotates. When the shoes need to be moved‚ they will loosen their grip and two metal “feet” will support the drill as the machine is pushed forward.
The TBM will generate about 1.6 million kilos of rock per hour. Buckets that line the periphery of the cutter head will scoop up the debris‚ called “muck‚” from the bottom of the tunnel and drop it onto high–speed conveyor belts‚ which will carry it to a pile off–site.
Engineers expect to remove about 1.6 million cubic metres of debris (enough to fill the Rogers Centre to the brim)‚ which will probably be used by the brick industry.
The drill will be able to go as fast as five metres an hour‚ but engineers expect it to move no more than 15 metres a day on average; although it will be operational 24 hours a day‚ only about 12 hours will be spent actively drilling. It will have to stop while construction workers stabilize the sides of the tunnel to prevent a cave–in.
Workers will line the 45–metre circumference of the tunnel with wire mesh. About every 1.2 metres‚ curved steel beams will be placed against the sides and hydraulically expanded to support the rock. Steel bolts‚ up to six metres in length‚ will anchor the wire mesh to the roof before sprayable concrete is showered onto the surface of the tunnel.
Afterward‚ a waterproof layer of concrete‚ about 60 centimetres thick‚ will be spread on the entire surface‚ leaving the tunnel with a final width of about 12.7 metres.
Although you might think that the sound from the 2‚600‚000–kilogram drill boring through rock would be ear–splitting‚ “you can more or less have a conversation with somebody at just a somewhat louder level‚” Mr. Kolenich says.
When he stood just behind a 10–metre cutting head drilling in Iceland‚ he says‚ “literally I could put a cup of coffee on the back of the machine and it wouldn’t spill a drop.”
As for the Niagara Falls drill‚ it will likely see more action. Robbins has the option of buying back the machine‚ which can be modified to a width of 9.8 metres for smaller projects. And as tunnels for highways‚ sewers and rail links are getting larger and longer (the world’s longest tunnel‚ the 57–kilometre Gotthard Base Tunnel in Switzerland‚ is currently under construction)‚ the company will probably want it back.
Drill bits
THE MACHINE
Total weight: 2‚600‚000 kilograms.
Cutter head: 14.4 metres in diameter; rotates up to five revolutions per minute.
Cutter discs: 85 in total‚ each about 20 inches in diameter.
Speed: Capable of boring about five metres an hour‚ but because of the need to stop and put up support structures‚ probably no faster than 15 metres a day.
Debris: eventually 1.6 million cubic metres of fractured rock.
THE TUNNEL
Project start time: Between late July and early September.
Completion: 2009
Length: 10.4 kilometres
Life expectancy: 90 years
Flow capacity: 500 cubic metres of water per second.
Electrical generation: An additional 1.6 billion kilowatt–hours a year‚ enough for 160‚000 homes –– an increase of 14 per cent at the Sir Adam Beck Complex.
Cost of entire project: $985–million