Tunnels subject to negative pressure.

[IsaacStructural]

I've heard that in New York they are pumping out water from the tunnels after hurricane sandy. There is concern they will create negative pressure and this cause problems. Can anyone expand on what these problems are? Is it just a concern about spalling concrete because of corrosion in the damp environment of a tunnel?

M.S. Structural Engineering
Licensed Structural Engineer and Licensed Professional Engineer (Illinois)

 

[dicksewerrat]

I don't see how they can create neg. pressure. They can't pump fast enough and the tunnels all are open to the atmosphere. There may be some closed off rooms that they are concerned about.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[IsaacStructural]

I don't know enough about the system, is it possible there are some localised located that drop in elevation or something and they might be fully filled with water? If so they could function like a P trap, and perhaps some level of neg. pressure would be possible.

Anyhow, just for discussion, if they did create negative pressure, is there much risk of a tunnel section collapsing inward, or is the risk more to spalling concrete, damaged seals between tunnel sections, etc?

M.S. Structural Engineering
Licensed Structural Engineer and Licensed Professional Engineer (Illinois)

 

[paddingtongreen]

I don't know who in NY is expressing the concern, but if it was me, and if I were an engineer on the system, I would be pretty annoyed that someone off on some forum cast a doubt on my concerns.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[bridgebuster]

I don't think it's a negative pressure problem. As dick said they're open to the atmosphere. Even though various tunnel sections below the East River are flooded these same subway lines are still operating on each side of the flooded areas.

 

[MikeHalloran]

Some coverage:

http://www.nytimes.com/interactive/2012/10/30/nyregion/hurricane-sandys-aftermath.html

Mike Halloran
Pembroke Pines, FL, USA

 

[MikeHalloran]

Map:

http://www.mta.info/sites/default/files/pdf/SubwayRecoveryMap_0.pdf

Mike Halloran
Pembroke Pines, FL, USA

 

[MikeHalloran]

Searched. First relevant negative pressure reference found was this thread.

Second one was this:

http://www.hydroworld.com/articles/...dating-the-design-of-an-intake-structure.html

... which deals with vortex formation at water intake structures, not really related to dewatering tunnels.



Mike Halloran
Pembroke Pines, FL, USA

 

[MikeHalloran]

The source of the concern may be a message from "Anon_User" here:

http://www.quora.com/Civil-Engineer...-they-suck-out-the-water-from-the-NYC-subways

Mike Halloran
Pembroke Pines, FL, USA

 

[miningman]

When dewatering mines that have been flooded for years we can get some interesting effects if we dewater localized areas too fast. However typically it is not the rock or the concrete that we have to be concerned about, it is areas that we have previously backfilled with tailings materials. These tailings usually have a relatively low permability and are usually initially placed behind substantial timber bulkheads, designed to drain excess water as fast as we place the material. If the mine has been allowed to flood we always assume these tailings are now 100% saturated and we have to ensure that the material behind the timber structures ( by now probably half rotted ) drains at the same rate as the dewatered tunnels in the area of the bulkheads. If not the timber bulheads are subject to hydraulic presures that they were never designed for and all of a sudden yoove got half a million tonnes of quicksand coming at you.

Extrapolating this to New York , its areas of saturated localised geology you have to worry about , not the tunnel itself.