On December 20, 2013, there was a briefing for media on the Eglinton Crosstown Project at Metrolinx.  Coming the morning after the Press Gallery’s Christmas party, this was a lightly attended event and it received scant coverage.

Tunnel Construction Progress

The tunneling is making better progress than expected.  Originally, the contractor had planned for 12m/day, but they are actually making 20m/day thanks to improved efficiency in removal of spoil with a conveyor system.

At Eglinton West Station, the project faces the problem of getting under the existing Spadina Subway structure.  Original plans called for an extended shutdown of the Allen Road and much of Eglinton Avenue so that the tunnel boring machines (TBMs) could be disassembled, extracted from the west side of the site, lowered into a new access shaft on the east side, and reassembled to continue their journey east to Yonge.

This scheme was not acceptable to the City of Toronto and a new proposal is under consideration.  The access shafts will be longer, but the TBMs will be extracted, moved and lowered back into place in one piece.  The move across the subway structure would be done similarly to rapid bridge replacement projects with a support structure to carry the TBMs (which weigh 420 metric tons) from the west to the east side.   This approach will eliminate the need to disassemble and reassemble the machines.

The eastern tunnel contract includes the launch shaft (between Brentcliffe and the west branch of the Don River), and work will begin there early in 2014.  The eastern tunnels will bore west to Yonge.

The two tunnel contracts – at $283-million for the west side and $177m for the east – are only part of the much larger cost of building an underground transit line.  The tunnels (of which the western section is now under construction) will be provided as empty tubes – physical structures with no installed systems – for the next stage in the project.  Tunneling will complete in 2016.

At each station site, headwalls are built at each end of what will become the station excavation.  As the TBMs reach the headwalls, they bore through and leave behind a completed tunnel that will be partly disassembled when the station construction digs down to them.  Two techniques are used for these walls depending on local conditions:

• Secant piles require boreholes into which the piles are installed.  These require utility relocations to avoid the boring activity.
• Jet grouting uses a slurry to form the headwalls without the need to bore.  This approach is being used at Caledonia Station.

The TTC assisted with specifications for the tunnels to ensure that they meet the standard of other Toronto infrastructure.  These will be constructed as empty round tubes that will be transferred to the bidders for the next stage of construction and who will take over the risk for future maintenance.

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