Tunneling at a maximum distance of 10 metres per day, it's going to take Alice, the Evergreen Line's tunnel boring machine (TBM), at least 200 days to create a two-kilometre underground train route from Port Moody to Coquitlam.
Named after Alice Wilson, Canada’s first female geologist, the TBM, worth about $20 million, is owned by SNC-Lavalin, the primary contractor for the $1.43 billion Evergreen Line rapid transit project.
It’s a long-standing tradition in the tunnel-boring business to give the massive machinery a nickname.
Big Bertha, Dennis and Lea are some of the at least 50 TBMs operating worldwide.
Alice, which started her underground journey in March, is 85 metres long, 10 metres in diameter, weighs 1,100 tons and runs via an electric motor.
She’ll operate at depths ranging from 17 to 50 metres.
Built by Caterpillar Inc. in Toronto, SNC Lavalin bought Alice new.
The Evergreen Line is her first project, said Jeff Spruston, a heavy civil engineer, who works for SNC-Lavalin as the contractor’s representative.
The Province of B.C. and EGRT Construction, a consortium led by SNC-Lavalin, have signed a deal to design, build and finance the Evergreen Line, a joint project between the federal and provincial governments and TransLink, which operates Metro Vancouver’s transit network.
The project also includes construction of an elevated track and six stations.
In a footnote, Caterpillar, which bought the TBM factory from Lovat Inc. in 2008, announced the surprise closure of the factory in May 2013.
Alice was one of the last TBMs built at the plant, which is to close this year.
After being built and tested in the Toronto factory, Alice was disassembled for shipping.
Moved across Canada by rail and truck, in about 20 different loads, it took about three months to reassemble at the north tunnel portal, located west of Barnet Highway in Port Moody, Spruston said.
Main components include the 130-ton cutter head, which does the actual excavation.
The screw conveyor removes excavated material from the face.
The belt conveyor moves the soil (glacial till) out of the tunnel.
As the machine moves forward, the segment erector installs pre-cast concrete segments (tunnel rings) that support the tunnel.
An inserter picks up segments and moves them into position.
Hydraulic jacks around the edge of the TBM retract for liner insertion and expand to hold segments in place.
The TBM pushes against the ring segments to move forward and steer left, right, up or down. The grout plant supplies grouting behind the segments.
The “muck” that’s generated as Alice bores her way through the glacial till is moved to a tunnel truck.
That muck is sent to a disposal site in Port Coquitlam and will eventually be used as fill in low-lying areas, Spruston said.
When Vancouver’s Canada Line was built, two tunnels were bored, one for northbound trains, one for southbound trains. It was done with one, smaller TBM that excavated one tunnel, then was moved to excavate the second.
For this line one tunnel will be bored to accommodate both the northbound and southbound trains.
The much larger diameter excavation will have a dividing wall installed, Spruston said.
To stay on schedule, Alice has been operating round-the-clock, usually with two, 10-hour work shifts and one four-hour shift for maintenance.
The machine has been working Monday to Saturday, but the schedule may be extended to seven days a week.
That decision will be made by mid-June, Spruston said.
About 70 people in three shifts work on site with another 25 staff.
The cutter head operator is a very specialized job.
The Evergreen Line project has two operators, one from Italy and a second foreign worker.
Thanks to well-established working methods, workplace injuries aren’t common.
Compared to underground drill and blast excavation, mechanical excavation by TBM is quite a bit safer, Spruston said.
However, problems can still occur.
The world’s biggest TBM, Big Bertha, which is 17 metres in diameter, recently broke down after digging about 300 metres underneath Seattle’s downtown waterfront.
The $3.1 billion project to replace the city’s Alaska Way Viaduct hit an underground roadblock when it struck a well pipe that damaged her cutter head and bearing.
Fixing Big Bertha might take until March 2015 and cost at least $125 million, which is $45 million more than was paid for the Japanese-made machine, according to the Department of Transportation.
Now the contract will be reviewed to determine who’s responsible for the delay.
Spruston said everyone in the tunneling community is aware of the problems with Bertha, adding that the work Alice is doing is in a much more common size range.
And Alice is not expected to face the seal or bearing problems that Bertha experienced.
“Furthermore, we have triple-checked our alignment for any possibility of encountering man-made materials, which may have been a contributing factor in Seattle,” Spruston said.
When Alice finishes the Evergreen Line, she’ll be sold to another contractor or to Caterpillar via a buy-back program.
TBMs typically have a tunneling life span of about 20 kilometres or about six jobs.
After each project, the machine needs to be rebuilt, said Spruston, who added that Alice can be modified for different soil or rock conditions.
B.C. MINISTRY OF TRANSPORTATION
The machines teeth contain sensors that indicate when they need to be replaced.