It's not in an earthquake zone, but isn't the Scandinavian continent still rising at a surprisingly fast rate? I wonder if that could affect the engineering of the Fehmarnbelt tunnel, in an "in x years one end of the tunnel will have risen n centimeters compared to the other end" way. It's probably such a small amount it's well within levels where regular maintance will cover it anyway, but I'm still curious.

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.

Here’s a fun video about how one sunken tunnel was built in Vancouver back in the 50s. https://youtu.be/A1igKk8eK0M

From a Danish perspective I don't really see any positive long, or short, term gains from the Fehmarn tunnel, but I also live in the wrong part of the country.

This is a tunnel for Sweden, Norway and Copenhagen, it's moving the center of everything in Denmark closer and closer to the center of Copenhagen, completely disconnecting the rest of the country. A few days ago a new train start running Copenhagen to Oslo, a seven hour trip. That's the same time it takes me to get to Copenhagen by train within Denmark. Everyone is happy that you can "Get on the train and just pop to Hamburg, Berlin or Prag", but you can't, only if you happen to live in a few select spots does that work. It's a multi-day journey with a layover within the country if I want to leave by rail.

Internationally this is a great project, internally in Denmark, it's going to make international train travel worse for the majority of the country.

I really hate how German environmental activists resort to hyperbole and alarmist language by default when voicing concerns. This only makes it harder for me to take them seriously.

And then there is this tried and true tradition of commissioning studies with the sole intent to support a predefined viewpoint rather than taking an unbiased approach. This makes it so hard to trust any information when political arguments become heated.

To make the connection back to the tunnel: it consumes a huge amount of concrete and that releases the associated amount of CO2. Thisnpart is fairly easy to estimate. But estimating the impact on traffic emissions is fraught with issues. There are so many assumptions about lifetime, amount of traffic, types of vehicles that I can easily imagine the error bars to stack up to the point where a little tuning of model parameters gives just about any desired result.