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The question has been surfacing periodically in the media and books over the past 100 years or so. I realize we're talking about a lot of material and work hours to begin with; the subsequent maintenance would be a nightmare. There are no power stations, nor radio towers between the continents; there is no viable way (or is there?) to build in vents along the way; the bottom of the ocean is uneven, and there's a mountain ridge in the middle; and who knows what problems would be encountered if the engineers decided to actually drill under the ocean floor all the way.

Pumping the air out might turn out to be extremely expensive. Leaving the air in might create problems for the trains: that's a lot of air in a tight space to push through.

How feasible is it? Or is it even technically possible to have a tunnel under the Atlantic?

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    $\begingroup$ These types of questions don't work very well for this site. As is often said, anything is possible, it is just a matter of cost. We have all of the engineering technology available to do large projects like this, but the feasibility is in the cost. Also, very large projects like this mean that there are literally thousands of things that could go wrong (and make the project unfeasible). That alone make the question too broad to answer. $\endgroup$ – hazzey Nov 14 '15 at 5:11
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    $\begingroup$ Technically possible practically not feasible. How about narrowing the question to something some realistic such as New Hudson Rail Tunnel. $\endgroup$ – Mahendra Gunawardena Nov 14 '15 at 12:48
  • $\begingroup$ @MahendraGunawardena: I agree we should be building tunnels and laying more track. That goes without saying. But it is transatlantic travel that has always fascinated me. I don't know how much longer the airline industry will be able to keep up with the rising costs. $\endgroup$ – Ricky Nov 14 '15 at 12:54
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I'm assuming you are asking about a tunnel between North America and Europe.

There are two types of tunnel that "might" be possible: excavating a tunnel through the rock beneath the sea bed or sinking prefabricated sections of tunnel to the sea floor, joining them up and sealing them against water inflow.

Problem #1 - Depth of the North Atlantic Ocean

The depth of the Atlantic Ocean is between 3700 and 5500 metres. Such depths are going to make it extremely difficult to sink the tunnel sections, assemble them, ensure they can survive the water pressure and be water tight.

Additionally, such deep water will increase the ground stresses in the rock in the sea bed, which will be problematic for an excavated tunnel.

Problem #2 - Geological Reconnaissance

For an excavated tunnel, the sea bed will need to drilled along the proposed path of the tunnel at closely spaced intervals so core sample can be taken, so that geologists can determine what type are rock or soil (sediments) are there and ascertain material properties for the rock. They will also need to know what geological structural discontinuities are present, such as faults, where they are located, how they are orientated and how adverse they could be.

Drilling in waters 5500 metres presents a whole lot of challenges, one of them being the drill string would be unsupported for the first 5500 metres of its length.

Geological reconnaissance would also be required for a sunk tunnel to ensure the sea bed could support the weight of the tunnel sections. Having sections of tunnel subside into soft sediments is something that would need to be prevented.

Problem #3 - Ventilation

Ventilation shafts rising though 5500 m of water would be problematic in terms of construction, support and possible impact by whales, ships or submarines. They would also need to be water tight to prevent water inundation of the tunnel.

The only way to ventilate such a tunnel would be via ventilation tunnels parallel to the main tunnel. These could double-up as service tunnels for inspections, maintenance and rescue, should there be a fire in the main tunnel.

For reasons of safety, ventilation tunnels would need to be duplicated, at least.

Ventilation fans would need to be placed at the ends of the vent tunnels. They would need to be large and they would consume a lot of electricity.

Problem #4 - Traversing an Active Volcanic Zone

There is an entity called the Mid Atlantic Ridge. This is an active volcanic zone that is pushing apart the continental plates that separate the Americas from Europe and Africa. This ridge is visible above the water on Iceland.

Putting a tunnel on or through the Mid Atlantic Ridge may not be possible. If it were possible, the tunnel would require regular maintenance to remedy damage done by the Ridge.

Putting ventilation tunnels through the Mid Atlantic Ridge would be give additional ventilation problems.

Overall

The distance between Canada and Ireland is close enough to 3000 km.

The cost of construction a trans Atlantic tunnel would be hideously expensive!

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  • $\begingroup$ The distance also means that the journy would take several hours, a EUROstar train gets up to 300 km/h which means 10 hours in the tunnel. I'd still prefer the 6 hour flight. $\endgroup$ – ratchet freak Nov 14 '15 at 17:08
  • $\begingroup$ @ratchetfreak: Actually, one of the proposal was a maglev train inside a vacuum tunnel, with the travel time of about an hour and a half, door-to-door, from New York to London. $\endgroup$ – Ricky Nov 15 '15 at 9:56
  • $\begingroup$ @ratchetfreak Change in fuel prices or a possible green takeover both in the EU and in the US can make this 4 hours spare unfeasible. $\endgroup$ – peterh says reinstate Monica Jan 9 '18 at 2:21
  • $\begingroup$ I am not sure, how often actual vulcanism plays a role in a human timescale. If you visit Iceland, you won't see continuous eruptions and molten lava all the day everywhere. You will see an icy island, with many thermal baths. $\endgroup$ – peterh says reinstate Monica Jan 9 '18 at 2:24
  • $\begingroup$ If it's gonna be a vacuum maglev tunnel, then vents won't still be such a big issue. Or? $\endgroup$ – GwenKillerby Dec 1 at 12:09

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