Third sinkhole forms at Evergreen Line tunnel boring stoppage site

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Evergreen Line tunnel boring machine

Another surface sinkhole has formed along the route of the SkyTrain Evergreen Line’s two-kilometre long bored tunnel.

This is the third sinkhole incident for the ongoing tunnel boring process under the Tri-Cities since last fall.

According to the Evergreen Line Project Office, a small sinkhole appeared in the middle of the road on Clarke Road near Seaview Drive on Thursday.

The tunnel boring machine was stopped at this location so that crews can perform maintenance on the machine. During this process, ground material entered the cutting head chamber and an air pocketed was formed, resulting in a sinkhole. These were also the same conditions that caused the first two sinkholes to form.

As a precaution, traffic patterns in the area have changed to allow crews to assess and repair the road. A cement mix will also be injected from the surface into the ground to strengthen the soil.

Until further notice, only one northbound lane in this section of Clarke Road will be open to traffic.

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.

Image: Evergreen Line Project Office

SEE ALSO: How it works: Evergreen Line tunnel boring machine (VIDEO)

The Evergreen Line construction project is managed by the provincial government’s Ministry of Transportation and built by private contractor SNC Lavalin. TransLink will operate and maintain this 11 kilometre, six station extension of Millennium Line infrastructure when the line opens for revenue service in fall 2016.

Project planners had originally planned for a mid-summer 2016 opening, but problems with the tunnel boring process has forced the government and contractors to push the opening to a later date.

Tunnel boring began in March 2014 was originally anticipated to take 200 days to complete – a rate of about 10 metres of new tunnel length per day.

Overall, as of last month, the entire Evergreen Line project is 60 per cent complete: elevated and ground-level track construction is finished while station construction is well underway and on schedule.

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