[rbt]

I get that, but are you saying that they will literally be trenching across Eglinton, or instead just continuing to dig the tunnel under the surface by other methods than the TBMs?

They will literally be trenching along Eglinton across/over/under Yonge.

The area above/below the subway line will be hollowed out, and the Yonge line reinforced structurally as they go. The new station will be built around the now reinforced section of Yonge line.

The risk of a Yonge line collapse using a TBM underneath the Yonge line is very high. Toronto soil is sloppy and requires a very large buffer to prevent existing structures from moving. This is, in fact, why Eglinton is 2 small bores instead of 1 large bore; small bores require much smaller buffer distances.

 

[JayBeeGooner]

The tunnels will be underpinned. Similar to how the Bloor Danforth was tunneled under the Yonge Line and the University Line at the time.
I believe there is a pic out there that shows the construction.

 

[Steve X]

It does, but bear in mind that in conventional cut and cover, the excavation may unearth things like sewers and water mains, and just leave these hanging in mid-air (I'm exaggerating, they are braced or supported) while the excavation continues downwards. A lot of the old photos of the Yonge Subway excavation show this clearly.

Excavating under the subway is much the same, albeit a bit bigger engineering challenge. The existing subway can "hang" in the air while things are built beneath it.

- Paul

I imaging they'll just going to do shoring. Instead of vertically, they'll excavate both sides and drill horizontally under the tracks and apply a layer of concrete. Then they can dig underneath. It's be similar to some of the mined stations. I believe they'll have an open house next week for Eglinton West.

 

[nfitz]

I apologize if this is a profoundly silly question that has been answered elsewhere, but: If the extraction shaft for the western TBMs is west of Yonge, and the extraction shaft for the eastern TBMs is east of Yonge, how will the part under Yonge actually be tunnelled?

It won't be. The station box between the two extraction shafts will be excavated - as the "diameter" is much larger than the TBM.

It's going to be a massive project - with the plan to move the existing Yonge line platforms at the same time.

I'm not even sure if it's part of the Crosslinx contract. Originally there was talk of TTC tendering this station (and Eglinton West - or whatever bizarre name that one is now) separately, so that Crosslinx didn't interfere with the existing line - but I'm not sure where that landed.

 

[barit]

It won't be. The station box between the two extraction shafts will be excavated - as the "diameter" is much larger than the TBM.

It's going to be a massive project - with the plan to move the existing Yonge line platforms at the same time.

I'm not even sure if it's part of the Crosslinx contract. Originally there was talk of TTC tendering this station (and Eglinton West - or whatever bizarre name that one is now) separately, so that Crosslinx didn't interfere with the existing line - but I'm not sure where that landed.

Not so much "move" the platforms but extending them north 30 metres.

 

[jcam]

Not so much "move" the platforms but extending them north 30 metres.

Are they losing a crossover or pocket track (from when Eglinton was the terminal) to extend/move the station north? I imagine this wouldn't be possible if there wasn't already width in the underground structure to accomodate it.

My understand is it will require 40+ weekend closures over a couple of years.

 

[rbt]

Are they losing a crossover or pocket track (from when Eglinton was the terminal) to extend/move the station north? I imagine this wouldn't be possible if there wasn't already width in the underground structure to accomodate it.

Not as far as I know. There is currently a mechanical area at the North end of Eglinton. This will be relocated and that space turned into customer space.

My understand is it will require 40+ weekend closures over a couple of years.

Yes, though the Davisville track rebuild also requires a large number of weekend closures and will occur at the same time. If you assume Davisville is absolutely necessary (which TTC does) then this Eglinton work is free.

 

[barit]

I believe the north pocket tracks were built when the line was extended north to Finch. I also believe said tracks will have to be removed. There is a report from the TTC about this posted back a bit, but I can't find it right now.

 

[someMidTowner]

The eastern TBMs have progressed another block forward:

 

[Steve X]

Seems like they'll be done by late summer not fall at this rate.

 

[Steve X]

If anyone is interested in reading the update for Eg West: http://thecrosstown.ca/news-media/whats-new/cedarvale-station-open-house

 

[Amare]

If anyone is interested in reading the update for Eg West: http://thecrosstown.ca/news-media/whats-new/cedarvale-station-open-house

Wow just reading all that boggles my mind. This is extremely complicated work just to construct one station, let alone the entire line. Now I feel sorry when construction workers have to deal with the public/NIMBYS and their constant whining about construction work.

If they dont want to deal with the noise all the time, they should let the contractors know so they can close Eglinton down 24/7 for cut and cover construction.

 

[Steve X]

Since the public doesn't accept closing down Eglinton for years, they have to carefully plan and stage it so traffic can still flow. It's probably easier for them to build Caledonia Station as it's off to the side instead of being right under the roadway.

 

[BurlOak]

If they dont want to deal with the noise all the time, they should let the contractors know so they can close Eglinton down 24/7 for cut and cover construction.

I am getting more convinced that cut-and-cover is a better way to go when tunneling under roads. Cut-and-cover sound like old technology. Tunneling and using fancy TBM's sound more high tech and modern, but it has its drawbacks. The stations are built using cut-and-cover anyways. Generally, the biggest traffic disruptions from road/lane closures happen at major interchanges - where the stations are. The largest concentration of population that is affected by the noise is at the major intersections.
In order to use tunneling, the bore must be extra deep to ensure no cave in during construction and minimize the load on the tunnel from traffic above. Thus, you see huge depths of stations and the cut-and-cover construction of the station cost and construction duration goes up significantly with station depth. If the whole line was cut-and-cover, the platforms and emergency exists are at a shallower depth since they don't have to be unnecessarily deep.

So tunneling minimizes the disruption mid-block where construction would be the least intrusive and significantly increases it at the intersections, where it is most critical.

I haven't seen the exact profile of the Eglinton line, but I understand that tunneling was used to smooth out the grade. It may be that at some locations, cut-and-cover would have been deeper than desired and a few locations may have had the mid-block cut-and-cover construction with more disruption than others.

 

[crs1026]

The thing about TBM is, you can't be selective about where you use it. It has to run end to end. As you say, cut and cover might be better in spots - but the TBM can't bypass a segment without extraction and reinsertion.

In this politically fickle city, the need to tear up a major street end to end might be enough to doom a project. So I'm happy to see TBMs used.

- Paul