The Gibraltar Bridge

[faded glory]

NYC's Verinzano is pretty big. Or I could be thinking of one of the other 5 massive bridges into NYC.

The one out to Key-west florida is huge. Like 10 miles or so...I remember driving it when I was a kid (err...riding.not driving)

[David James]

I remember watching a Discovery documentary about this and other ridiculous to insane engineering projects.

The underway geography of the straits (cross section) is like a 'W', except the middle peak is still quite deep. The trenches are extremely deep. Because of this, a tunnel is completely out of the question. A suspension bridge is the only real option, with a middle support built on however many million tonnes of concrete is necessary to reach the middle peak.

Why one would waste time and money on such a thing is beyond me. All it will do is end up being a conduit for illegal immigrants to Europe from all of Africa and serve no other meaningful purpose. I certainly don't envision too many private investors lining up to foot the bill (although they might willingly lend to a government to do such a thing). Besides all that, the bridge would become a very juicy terrorist target - imagine protecting a kilometre deep column of concrete from attack. Hell, they could probably infiltrate the construction crews (sure to be drawn from North Africa and beyond) and plant it during construction for detonation a few months or years into the future. Knowing the EU, they would probably even employ the bin Laden family's construction company as contractors.

[KrazyHorse]

Originally posted by Asher
I don't know if it'd be called a chunnel, since it's not a channel it's being dug under, no?

If the water's a thousand meters deep, a tunnel is a silly idea...

[TCO]

What's the deepest tunnel that has been built?

[KrazyHorse]

Don't know...

Appears to be the Hitra tunnel in Norway which hits max. depth of 264 m and is 5 645 m long.

[TCO]

1. Does the tunnel feel the pressure of the column of earth above it? (Assuming yes...that would be over a thousand psi. Figuring soil as twice the density of water or more.) Wonder how they shore it.

2. How deep is the chunnel? Didn't realize that it was so shallow over there. But I'm a PAC sailor...

[KrazyHorse]

2) Average depth of Chunnel = 150 ft, according to eurorail. That probably puts max depth somewhere near 100 m.

1)a) Why column of earth? Hitra is undersea tunnel...

1)b) Probably not. Would feel some increase, but soil acts more like solid than fluid when packed. In other words, it's self-supporting...

[TCO]

Interesting to think about. Wonder what the deepest "under mountain" tunnel is. I guess that would have to be through rock and maybe it is shaped to be self-supporting. Wonder if earth transfers the pressure more than rock.

[The Mad Monk]

The problem isn't just the water, it's also the subduction zone. Imagine the sea floor as a conveyor belt. At the mid-ocean ridges crust is being formed and pushed out to the tune of a couple or a dozen cm a year; this crust spends the next forty million years or so moving under the sea, and then is shoved under a continent and back into the planet at subduction zones.

This process is more or less continuous, and any debris collected on the sea floor during its travel goes down the subduction zone along with it. As a result, not only do you have to deal with the huge water column (because the crust is literally diving into the planet), you have to deal with hundreds or thousands of meters of unconsolidated rock that's slowly being ground into mud below the 'surface' of the trench.

At least until pressure and temperature are such that the mud is either squeezed into rock or melted -- of course, that adds a whole new set of engineering problems...

[Eli]

Build it, and keep it closed.

Just to see if we can.

[Zoid]

Provost: The Akashi-Kaikyo Bridge, connecting Kobe on the mainland with Awaji on Awaji Island, will be a huge three-span cable-stayed bridge some 3910 meters in total length with a center span of 1990 meters. When completed, it will be the longest bridge of its type in the world, surpassing the Humber Bridge in the U.K......but I guess you knew that already?