[jmi22]

Tunneling to protect trees and forest is atrocious from a carbon perspective.

I know as a society we care very little about the excess use of concrete, but we have to start at some point if we're going to do anything about apocalyptic climate change.

Exactly, we can either build electric transit affordably with a painful, but not disastrous short term environmental cost, or not build it at all and allow gas guzzling sprawl to continue consuming farmland and forest outside the GTA.

 

[jmi22]

As opposed to all of the concrete that will be shaped and poured for the guideway?

Dan

Supporting the weight of a train and track requires much less concrete than preventing a tunnel with 50ft of dirt and stone above it from collapsing. And from an overall carbon perspective, the amount of gas burned in order to tunnel bore and excavate is immense compared to building what is functionally a single story structure.

A quick screen grab from the testing of the Eglinton LRT shows rolling stock entombed in concrete, that extends far behind the tunnel walls visible to a rider. On the contrary, the Davenport Diamond is a flat deck of concrete with support posts ever 10mish. This is no hard science but one is clearly using less concrete.

 

[reinventingthewheel]

On the contrary, the Davenport Diamond is a flat deck of concrete with support posts ever 10mish. This is no hard science but one is clearly using less concrete.

And this deck would even be considered overdesigned for a much lighter weight metro!

 

[micheal_can]

Trying to compare the amount of concrete for the 2 projects is misguided without the facts of how much is actually needed. Why not search for projects that did tunnels and raised guide ways and get the cubic meters per km of each? Then we have a good comparison.

 

[smallspy]

Supporting the weight of a train and track requires much less concrete than preventing a tunnel with 50ft of dirt and stone above it from collapsing. And from an overall carbon perspective, the amount of gas burned in order to tunnel bore and excavate is immense compared to building what is functionally a single story structure.


View attachment 515703View attachment 515704

A quick screen grab from the testing of the Eglinton LRT shows rolling stock entombed in concrete, that extends far behind the tunnel walls visible to a rider. On the contrary, the Davenport Diamond is a flat deck of concrete with support posts ever 10mish. This is no hard science but one is clearly using less concrete.

A lot of the strength of a tubed concrete structure is due to its shape. All of the tunnel liners are shaped to lock into themselves, and are then reinforced to each other with long bolts. The pieces that form the walls are surprisingly thin, only about 12 to 15 inches or so. Beyond that distance is just dirt and sometimes grout, but in the context of something like a tunnel the amount of grout is negligible when compared to the amount of concrete.

With the elevated guideway, a box (chambered girder) is required for strength under each track. And it's surprisingly deep - in this particular case I believe that the box is about 8 feet from the top surface to the bottom. While the box is hollow, the walls are almost the same thickness as those for the tunnel liners.

The volume of the pillars on the elevated guideway is not inconsequential, either - they go down far more than what you see above the surface.

Feel free to do the maths on this, but I suspect that you'll see that the difference per foot of length is not so great.

Dan

 

[CapitalSeven]

Let's mention that the bottom of the valley is about 40 meters lower than Pape and Overlea. The two stations on either side of the valley would have to be extremely deep, expensive, and inconvenient were it tunneled.

 

[Northern Light]

Tunneling to protect trees and forest is atrocious from a carbon perspective.

I know as a society we care very little about the excess use of concrete, but we have to start at some point if we're going to do anything about apocalyptic climate change.

Except for the fact that this is not true, its a fine thought.

@smallspy has provided useful comment above on the carbon impact of an elevated guideway, which you clearly underestimate.

Likewise, you note a (possible) one-time carbon savings by (not) tunnelling; but fail to note that trees remove carbon every year of their lives. So the correct comparator is total carbon removed by said trees annually x the life cycle of the concrete in the tunnel or guideway.

 

[Northern Light]

Let's mention that the bottom of the valley is about 40 meters lower than Pape and Overlea. The two stations on either side of the valley would have to be extremely deep, expensive, and inconvenient were it tunneled.

At no point did I suggest tunnelling under the Don river/valley. Crossing the Don Valley would be on a bridge, and some trees would be removed in the process of building said bridge regardless. The issue is tunnelling under Overlea on the north side, with a more limited impact crossing of the West Don valley where the existing road bridge is over E.T. Seton and avoiding the Walmsley Brook valley entirely vs the choices made.

 

[afransen]

A lot of the strength of a tubed concrete structure is due to its shape. All of the tunnel liners are shaped to lock into themselves, and are then reinforced to each other with long bolts. The pieces that form the walls are surprisingly thin, only about 12 to 15 inches or so. Beyond that distance is just dirt and sometimes grout, but in the context of something like a tunnel the amount of grout is negligible when compared to the amount of concrete.

With the elevated guideway, a box (chambered girder) is required for strength under each track. And it's surprisingly deep - in this particular case I believe that the box is about 8 feet from the top surface to the bottom. While the box is hollow, the walls are almost the same thickness as those for the tunnel liners.

The volume of the pillars on the elevated guideway is not inconsequential, either - they go down far more than what you see above the surface.

Feel free to do the maths on this, but I suspect that you'll see that the difference per foot of length is not so great.

Dan

Station boxes are also pretty significant concrete sinks.

 

[Undead]

Isn't this missing the forest for the trees? Sure the subway line will use concrete, like any project. But how many car trips does it prevent? How many bus trips are shorted/eliminated because of it? The line is a massive net benefit in the bigger picture.

 

[generalcanada]

Isn't this missing the forest for the trees? Sure the subway line will use concrete, like any project. But how many car trips does it prevent? How many bus trips are shorted/eliminated because of it? The line is a massive net benefit in the bigger picture.

Ive been told that if you add all the projects up together the trees become a forest.

or so ive heard

 

[desperateAmbassador]

From a carbon perspective only - urban tree removal is a red herring. You could clear cut every tree in the GTA and the net carbon impact at a global level would be negligible. Trees provide ecological habitat, shade, aesthetics and livability and should be protected for those reasons. But carbon sequestration is not a good argument in the context of a hundred or even a thousand trees for a construction project (an all-electric mass transit project no less).

 

[Northern Light]

Isn't this missing the forest for the trees? Sure the subway line will use concrete, like any project. But how many car trips does it prevent? How many bus trips are shorted/eliminated because of it? The line is a massive net benefit in the bigger picture.

From a carbon perspective only - urban tree removal is a red herring. You could clear cut every tree in the GTA and the net carbon impact at a global level would be negligible. Trees provide ecological habitat, shade, aesthetics and livability and should be protected for those reasons. But carbon sequestration is not a good argument in the context of a hundred or even a thousand trees for a construction project (an all-electric mass transit project no less).

Guys, enough!

No one is saying save the trees, and cancel the transit line. This completely made up, bogus, and deeply offensive straw man keeps getting raised and I will be perfectly clear, it reeks when someone makes an argument based on an entirely false pretense.

The suggestion is simply that an alternative alignment, a whole block away, tunneled instead of elevated for a distance of ~ 2km would have been preferable. Moreover, it would have taken more cars off the road.

The as-being-built alignment manages to miss one of the largest middle schools in the City, and a High School that between them represent about 3,000 potential riders daily riders, not to mention leaving the southern 1/2 of Flemingdon Park underserved.

 

[CapitalSeven]

At no point did I suggest tunnelling under the Don river/valley. Crossing the Don Valley would be on a bridge, and some trees would be removed in the process of building said bridge regardless. The issue is tunnelling under Overlea on the north side, with a more limited impact crossing of the West Don valley where the existing road bridge is over E.T. Seton and avoiding the Walmsley Brook valley entirely vs the choices made.

My apolgies for misunderstanding. I always thought this your suggestion was what they would ultimately do. But whoever planned the Ontario Line pushed through on building elevated wherever they could (despite what is happening on Eglinton West for a lot few riders in a wider space). There are nearly 50 metres between facades along Overlea, and that wide space along the north side seems just begging for a right of way. It's not going to be pretty, but it's saving money and vegetation ultimately grows back.

 

[EnviroTO]

A quick screen grab from the testing of the Eglinton LRT shows rolling stock entombed in concrete, that extends far behind the tunnel walls visible to a rider. On the contrary, the Davenport Diamond is a flat deck of concrete with support posts ever 10mish. This is no hard science but one is clearly using less concrete.

I'm not saying you are wrong on the amount of concrete being more, but entombed in concrete is a bit of an overstatement. Most tunnels are built with precast concrete tunnel liners and not some guy who dug a hole and is filling it all back in over-zealously with concrete. Also, unless the tunnel is running through a liquid, the tunnel does not need to carry the whole weight of what is above it and the shape of the tunnel is about reducing the load the tunnel needs to support. Lastly, unlike an elevated structure the tunnel does not need to lift the train above the ground... it sits on the ground beneath it so it doesn't require cement columns going deep into the ground. So, maybe there is more concrete in a tunnel than an elevated structure but if so I doubt it is by the order of magnitude you think it is.