The Transbay Tube carrying BART across the bay is immersed tube. The sections were welded together by divers. The sections were filled with water and then pumped out.
Fehmarnbelt tunnel sections are concrete. I couldn't find how they are connected by concrete would make sense.
A video posted in another thread says the segments are sealed with bulkheads, floated into position, submerged by allowing water into a ballast section, dropped into place , aligned with pins, drawn to the next segment with hydraulic jacks, and sealed to it with rubber gaskets. Then the bulkheads can be removed. The gaskets also allow for some thermal expansion.
I'm curious what the lifetime of those gaskets might be and how you might maintain them.
The Merced to Bakersfield IOS looks like a bargain on a distance basis. I have no idea of the carbon offset or passenger time saving versus flying of course
Well, if we’re comparing CA infra costs, for a more 1-1 comparison you can look at the $9.7B Los Angeles is spending on building out a long-awaited subway line (phase 1 of 3 opened Friday!) and see how tunneling underwater looks like a bargain in comparison.
Fehmarnbelt tunnel sections are concrete. I couldn't find how they are connected by concrete would make sense.
I'm curious what the lifetime of those gaskets might be and how you might maintain them.
8B USD for 11 miles
CACHSR IOS 36B USD for 171 miles.
The Merced to Bakersfield IOS looks like a bargain on a distance basis. I have no idea of the carbon offset or passenger time saving versus flying of course
https://www.latimes.com/california/story/2026-05-07/los-ange...