3 ms·

I'm amazed that engineers can make submerged tunnels work and that leaks don't (literally) sink the whole plan.

• ianburrell 5mo ago
  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.
  • imglorp 5mo ago
    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.
    • bobthepanda 5mo ago
      I figure once you join them, you could also apply waterproofing to the outside as well, no?
      • lmm 5mo ago
        Maybe. What would that look like, adding more gaskets on the outside? That sounds even harder to maintain since the only way to get access is diving.
        • deleted 5mo ago
          [deleted]
        • euroderf 5mo ago
          Some kind of goop that would get very slowly squeezed into gaps by water pressure ?
          • usrusr 5mo ago
            Sealing is really not that difficult if you have access to the high pressure side. The hard part is identifying the location of the leak. In sum, this means that they have to absolutely nail it, on the first attempt, for the bottom part that is resting on the sea floor. If they can to that, the rest of the circumference will also be so good they don't have to even think about fixability.
        • tokai 5mo ago
          The sections are laid in a trench and covered by sediment. There's not going to be any routine maintenance by divers.
    • SoftTalker 5mo ago
      The "ballast sections" may act as bilges, so that any leaks will accumulate there and can be pumped out. 100% water-tightness is not essential. Occasional re-grouting/caulking of the joints may be good enough.
    • poizan42 5mo ago
      They are GINA gaskets[0], they were supposed to last 120 years[1], but it has recently been shown that they may deteriorate faster than previously expected due to being under constant compression[2][3] [0] https://www.trelleborg.com/en/marine-and-infrastructure/media/in-the-news/tailor-made-sealing-systems-for-the-fehmarnbelt-immersed-tunnel https://www.trelleborg.com/en/marine-and-infrastructure/medi... [1] https://www.trelleborg.com/marine-and-infrastructure/-/media/marine-systems/resources/case-studies/downloads/keeping-immersed-tunnels-watertight-for-120-years.pdf?rev=30fcb4a6a6f04555afe7c96290dae4ab https://www.trelleborg.com/marine-and-infrastructure/-/media... [2] https://www.sciencedirect.com/science/article/abs/pii/S0886779825008909 https://www.sciencedirect.com/science/article/abs/pii/S08867... [3] https://dailygalaxy.com/2026/03/rubber-used-in-undersea-tunnels-decay-fast/ https://dailygalaxy.com/2026/03/rubber-used-in-undersea-tunn...
      • imglorp 5mo ago
        Interesting! The spec sheet actually says 170 years but maybe they add some safety factor. https://www.trelleborg.com/marine-and-infrastructure/-/media/marine-systems/sustainability/gina-gasket-mrpi-epd-trelleborg.pdf?rev=06d95e35d0a24613a6ee081b8c83c015 https://www.trelleborg.com/marine-and-infrastructure/-/media...
  • bloggie 5mo ago
    Here’s a fun video about how one sunken tunnel was built in Vancouver back in the 50s. https://youtu.be/A1igKk8eK0M https://youtu.be/A1igKk8eK0M
• tekla 5mo ago
  The almost insane genius Brunel and the insane Thames Tunnel Project which was deep enough that workers suffered the bends. https://en.wikipedia.org/wiki/Thames_Tunnel https://en.wikipedia.org/wiki/Thames_Tunnel