Then... there are queries that come in that I really have no idea how to answer. So I point out logic flaws that seem obvious to me (at least) and generally ask for some sort of clarification.
Q: Can you go under Hawaii?
- Christopher P
A: Your question makes no sense. Hawaii is a chain of volcanoes in the central Pacific Ocean. Islands do not float on water.
Q: Can you go under any land mass? Real question by the way.
- Christopher P
A: The deepest drill hole (Novaya Zemlya, Siberia) went to about 10 km. It cost somewhere in the tens of billions of rubles, and took 5+ years to drill, with several fails that had to be cut off and by-passed. The deeper you try to drill, the higher the cost and the complications - both are exponential. At 4 km depth in a diamond mine in South Africa, the rock temperature is already up to 60 C. Miners work only because refrigerated air is pumped down to them... and by the time that refrigerated air reaches 4 km depth, the increased pressure has raised its temperature to 45 C. Incidentally, any air gap in the rocks at even much shallower depths is inherently unstable, and it's just a matter of when, not if, it will fail catastrophically. Rock bolts are insurance, but not a guarantee. Hot rock will always close in on the drill stem, even if you can afford to put steel casing into a hole 10 km deep. Any regional strain pattern will soon deform that casing, and trap the drill bit below it.
Except for bragging rights (and perhaps some limited scientific data), it's hard to imagine what argument was made to Soviet bureaucrats to justify expending so much money for a deep drill hole.
You can TUNNEL under mountains, or cities, and the London Underground and New York subway systems are more than a century old. It gets more expensive with time, as safety concerns and wages inevitably keep expanding. The Alaskan viaduct tunnel project in Seattle has been underway for many years, with the original budget of $2.8 Billion and a portal-to-portal length of about 2.8 km. It is still not done, and I'm not sure anyone has a clear idea of the final cost. Or when. Or for that matter, IF.
The BART system that goes under San Francisco Bay was really a dredge-and-lay operation, with reinforced concrete tubes fabricated and laid end to end in a big trench, and then sealed. At least sealed as well as part can be done. Pumps must operate 24/7 to keep it from filling up with seawater. The Chunnel from Pas-de-Calais France to Folkstone, UK, took about 6 years to build, and cost about $7 billion. It's about 38 km long under the Channel itself, and it gets about 75 meters deep at the lowest point. The Seikan Tunnel in Japan is longer, at 54 kilometers long and deeper, reaching 240 meters below sea level. I have personally developed and patented a technology that uses active electronic streamers dragged along the seafloor behind a ship. No matter how carefully I pot the take-outs, it's not a matter if IF, it's a matter of WHEN they will fail from saltwater intrusion at just 30 meters depth (that’s 8 times normal air pressure at the surface). For a 5-week offshore survey east of South Africa, we shipped down three different streamers. Two had failed, and the third was failing by the end of the survey.
Detroit automakers used to call this sort of thing Planned Obsolescence.
Bottom line: the costs - and risks - are so high that there must be a truly compelling reason to tunnel under any landmass, even for short distances. Tunneling under the seafloor is even harder and more expensive because you have to factor in some serious pumps and redundancy. When there is salt water that can reach any tunnel, then the integrity of any metallic components are going to be compromised with time, and you must factor in replacement-type maintenance. Just like airplanes.