How it works: Evergreen Line tunnel boring machine (VIDEO)
There has been much chatter in recent months over how the tunnel boring process for the SkyTrain Evergreen Line works. But how exactly does it work?
Alice, the Caterpillar-built tunnel boring machine, weighs 1,100 tonnes, is 85 metres long and 9.84 metres in diameter. She first started her journey in early-March 2014 and is drilling downhill deep below the Tri-Cities at depths between 17 to 60 metres.
The Evergreen Line’s underground segment spans 2.2 kilometres beginning near Clarke Street, traveling under Clarke Road and emerging just before Como Lake.
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Engineers had originally intended to have the machine drill approximately 10 metres per day to complete the tunnel in a 200 day timeline, but they are behind schedule. To date, more than half of the tunnel span has been complete, forcing project managers to move the SkyTrain extension’s scheduled mid-summer 2016 opening to fall 2016.
According to the Evergreen Line Project Office, tunnel construction is considerably slower than anticipated due to poor soil conditions as the tunnel runs through loose glacial till deposits. The tunnel boring machine’s drilling head has also required more maintenance, a process that requires stoppage of the machine. These conditions also caused small ground level sinkholes to form at a pair of locations where the tunnel boring machine stopped for maintenance.
Fortunately, given the issues at hand, the tunnel boring machine will only have to make a single pass – the tunnel is significantly wider than the Canada Line’s twin bored tunnels under False Creek and downtown Vancouver. This enables planners to fit a pair of tracks in both the inbound and outbound directions.
The Ministry of Transportation is overseeing the construction of the Evergreen Line, which is being constructed by Montreal-based SNC Lavalin while the tunnel boring project component of the project was subcontracted to Italy’s SELI. Both companies also built the Canada Line and will be responsible for any Evergreen Line construction cost overruns.
While the Evergreen Line’s tunnel boring process has gained the most the public attention over the past year, it is not the only tunnel boring project in the region.
Metro Vancouver Regional District is tunnel boring a one-kilometre long, $240-million water supply tunnel under the Fraser River just west of the Port Mann Bridge. However, this project has also experienced its own set of issues causing project planners to push the boring completion date from late-2014 to fall 2015.
In October, the machine experienced issues about 800 metres into the route. Boring stopped to allow repairs to be made. When the water pipe is installed in 2016, this project will provide a new water link between Coquitlam and Surrey.
The region’s largest and most challenging tunnel boring project is still the recently completed $820-million Seymour Capilano Water Filtration Project – a project consisting of two side-by-side colossal 7.1 kilometre long tunnels under Grouse Mountain using two boring machines. The tunnel reaches depths of 640 metres beneath the mountain, bored into hard granite rock.
Before boring at Grouse Mountain could occur, workers had to dig a 183-metre deep, 40-metre wide shaft into Seymour Mountain to launch the tunnel boring machine at its proper depth. Another shaft 271-metres deep, 40-metres wide was also dug at Capilano Reservoir to link the tunnels with a new pumping station.
This project was plagued with lengthy delays and construction cost overruns. Project planners with the regional district even switched tunnel boring contractors mid-way through construction.