Tunnels!

Roads - Rails - Sidewalks - Bikeways
talindsay
Wells Fargo Center
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Joined: September 29th, 2012, 10:41 am

Re: Tunnels!

Postby talindsay » January 4th, 2021, 11:51 am

Back in 2003 I asked a Met Council person why they hadn't considered elevating the (Hiawatha) line through downtown to remove grade conflict and the dude laughed dismissively, saying it would interfere with the skyways. That seemed like an unsatisfactory response to me, but Metro Council has clearly never taken elevated lines in the downtown seriously. And to be fair, they *are* ugly and disruptive, and the skyway problem is real.

I've also heard that our tunneling costs are relatively low compared to most places, and so the cost difference between elevating and tunneling is smaller than in most places. Basically if it's not worth tunneling here, it's not worth elevating either given the small difference in cost and the substantially higher disruption and environmental impact of elevated rail.

DanPatchToget
Foshay Tower
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Re: Tunnels!

Postby DanPatchToget » January 4th, 2021, 12:02 pm

While Miami doesn't have skyways (that I know of) their Metro Rail is elevated above their People Mover system in downtown, so that's probably the closest example of what elevated rail in Downtown Minneapolis would look like. I don't think anyone is proposing building the tracks through the skyways and then we have to deal with many grade crossings in skyways, but rather have the tracks go above the skyways.

Tcmetro
Wells Fargo Center
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Location: Chicago (ex-Minneapolitan)

Re: Tunnels!

Postby Tcmetro » January 4th, 2021, 12:40 pm

I think the downtown at-grade alignment is fine. Considering there's no long-term plan to add a third line to the 5th St corridor there isn't much need. I'd even be surprised if 7.5 min peak frequencies come back before the next decade.

As for the cheap tunneling, I believe it was first considered in the late 60s. The idea is that limestone is relatively easy to dig through. The problem is that the limestone layer is like 80 feet below ground, so stations would be quite expensive to build. The initial subway plan had stop spacing of 1-3 miles.

DanPatchToget
Foshay Tower
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Re: Tunnels!

Postby DanPatchToget » January 4th, 2021, 2:26 pm

I think the downtown at-grade alignment is fine. Considering there's no long-term plan to add a third line to the 5th St corridor there isn't much need. I'd even be surprised if 7.5 min peak frequencies come back before the next decade.

As for the cheap tunneling, I believe it was first considered in the late 60s. The idea is that limestone is relatively easy to dig through. The problem is that the limestone layer is like 80 feet below ground, so stations would be quite expensive to build. The initial subway plan had stop spacing of 1-3 miles.
From a near term perspective yes the 5th Street Corridor does the job. Long term however, I don't think it's in our best interest to rely on a corridor that's already at capacity.

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Nick
Capella Tower
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Joined: May 30th, 2012, 9:33 pm
Location: Loring Park, Minneapolis

Re: Tunnels!

Postby Nick » January 6th, 2021, 10:57 pm

Man, does anybody remember the argument on here like six or seven years ago about whether or not train frequencies would increase on 5th Street with the Blue and Green Line extensions?

Anondson
IDS Center
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Location: Where West Minneapolis Once Was

Re: Tunnels!

Postby Anondson » January 7th, 2021, 3:47 pm

All the time.

Tom H.
Rice Park
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Joined: September 4th, 2012, 5:23 am

Re: Tunnels!

Postby Tom H. » January 10th, 2021, 1:46 pm

Vividly.

Anondson
IDS Center
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Joined: July 21st, 2013, 8:57 pm
Location: Where West Minneapolis Once Was

Re: Tunnels!

Postby Anondson » January 16th, 2021, 11:07 am

So what is the geological extent of this pressed sand layer which was mined by the Ford plant?

I understand the greatest costs to subterranean transportation are to stations, but if this layer is this stupendously easy to excavate how far does it stretch underground?

https://www.startribune.com/did-ford-mo ... 600006618/

luigipaladio
Nicollet Mall
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Joined: May 14th, 2019, 1:56 pm

Re: Tunnels!

Postby luigipaladio » January 16th, 2021, 12:49 pm

The Twin Cities are underlain by layers of sandstone and limestone. You can get an idea of the geology by taking a look at the cliffs on either side of the Mississippi gorge in St. Paul and to some extent in the gorge between Minneapolis and St. Paul. The University has a couple of buildings that were tunneled at least ten stories below the surface for the advantages of a stable year round temperature and security among other potentials.

The limestone is loaded with spectacular fossils in many areas - not of dinosaurs, but of sea creatures dating back to a period when this region was a sea bottom.

There are problems in some areas, such as parts of Downtown Minneapolis, where underground streams have eroded considerable voids in the layers of stone, but by and large, both the limestone and the sandstone are relatively stable - as long as they are not exposed to weather conditions or high volumes of water (think about the rapid erosion of St. Antony falls when the flour millers built numerous tunnels to funnel water to their mills).

As a kid - this dates me - I toured the sand mines under the Ford plant. This was before the word "Liability" was a big factor in daily life. The "sand" was stone until it was ground up. As rock goes, sandstone is relatively easy to mine. With the high water table and numerous underground springs and streams, I suspect any effort to do an extensive system of deep tunnels would have more than a few challenges - not unsolvable, but expensive.

Anondson
IDS Center
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Location: Where West Minneapolis Once Was

Re: Tunnels!

Postby Anondson » February 11th, 2021, 6:44 am

Maybe tunneling under downtown would be a bad idea.

https://www.theguardian.com/environment ... hington-dc

DanPatchToget
Foshay Tower
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Joined: March 30th, 2016, 1:26 pm

Re: Tunnels!

Postby DanPatchToget » February 11th, 2021, 12:37 pm

Keep in mind New York's subway system is very old, so of course ventilation systems probably won't be as advanced there as modern subways. I wonder if their subway trains used to have brake shoes made with asbestos back when that material was common. If that's the case then at least that stuff isn't in the air anymore.

I remember when I was in Oslo in 2018 they had a few small plants growing on the platforms for the regional trains serving the underground Nationaltheatret (National Theatre) Station to make the air cleaner. I don't know if that's still going on and if it's worked, but a modern subway can still have modern ventilation.

alexschief
US Bank Plaza
Posts: 768
Joined: November 12th, 2015, 11:35 am
Location: Philadelphia

Re: Tunnels!

Postby alexschief » February 11th, 2021, 2:30 pm

Yeah, this is a problem to be solved, not a fatal conceptual flaw.

Air filters, better ventilation, different brake technology, etc.


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