Since it's a maglev and all cars are motor cars (true?), i'm thinking you could send the cars in such frequency that their vibracions interfere destructively with each other, resulting in a zero net vibration caused by the train.
You still have to deal with the weight of the train, which I figure will not be less than several hundred tons.
Ugh... 30m is around 4 atm.... less than 6, but it's still quite a bit of pressure.
30m is the absolute minimum distance to avoid shipping (I don't know about weather), and for safety's sake I'd want it a bit more, below where a guy in a scuba-suit could get to.
I think the only reasonable depth consideration is to avoid being obstacle for ship traffic.
Currents, waves, buoyancy ... are something which the Archimedes ( submerged ) bridge can handle via adjusting its waving with the external forces, even utilizing them ...
WTF are you talking about?
Come to think of it, where does the 6m width figure for the tunnel come from?
I figure 6m is about the minimum needed to allow a pair of 1973 Tube Stock (London Underground) trains to pass each other. That is, I figure the
minimum, bare-bones size any tube could be, and makes no account for any sort of safety measures.
So, do you really need a vacuum-filled tunnel because I don't see how it can work?
Without vacuum what the fastest you could go, a few hundred kph? The emptier the vacuum the faster it can go. Mind you, the emptier the vacuum, the more engineering issues you have as well.
One way (maybe) to do away with the issue of joints is to print the tunnel on a 3D printer hung in water below a big ship (think, Maersk E-Class big) like an old America's cup monohull with the bulb on the end of the keel. This of course presents its own problems, like time, if you're printing at 1mm/second you're making 86.4m/day, at which point a 4,900 km tunnel is going to take you 155 years to complete. Jointless tunnel though

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