Longest road and rail tunnel is being built under the Baltic Sea | Hacker News Reader

Longest road and rail tunnel is being built under the Baltic Sea

cnn.com

31 pointsvintagedave33 comments

I live in southern Sweden and while stopping at Bordershop and waiting for the ferry is not the worst thing in the world if you're going by car, this will be a huge improvement for traveling to Germany by train.

"Weighing in at 73,000 metric tons each, they will be as heavy as more than 13,000 elephants."

I'm pretty sure more people have an intuitive sense for how heavy a ton is compared to elephants.

> more people have an intuitive sense for how heavy a ton is compared to elephants

Yeah, I think most elephants don't have a good sense of _any_ man-made unit.

I take the Copenhagen <-> Hamburg train a few times a year, and this will make a pretty major difference on the Skåne / Germany journey. Though next time I’m taking Snälltåget over night, so maybe that’s easier still?

What's the mass of an unladen elephant? An Indian elephant or an African elephant?

There used to be train service on that ferry as well. Fond memories, in particular from the time when it was operated with the ICE-TD pseudo HSR (a diesel train, because German railroad is embarrassingly allergic to investment into any parts of the network that might be involved with crossing borders). Train goes into the ship, passengers disembark the train to stroll around the ship, just enough time passes for two cans of Tuborg out in the wind (benefits of not driving) and then it's back to the train again.

This is a better article with a map

https://www.geoengineer.org/news/casting-of-fehmarnbelt-tunn...

Thank you. I read that the tunnel "will link Denmark and Germany" and I had to check a map to confirm that yes, they are already linked. By land. By a lot of land. You're not experiencing memory loss.

> The Fehmarnbelt tunnel is going to be placed on a dredged tunnel trench, more than 90% of which has already been completed.

This is fascinating. I had thought underwater tunnels were always creating by boring, like the Chunnel was. But this looks like they're dredging a trench, placing cast concrete segments in it, and then filling in over the top. In order words, much like how the first subway tunnels were built a century ago on dry land, but now underwater.

I wonder how it's reliably kept waterproofed (on the span of decades or centuries)? How are the segments joined and sealed?

It is now done quite often for tunnels crossing rivers - just build the tunnel in a bay next to the river, then fllod it, float the tunnel in place and sink it to the trench, then cover with ballast and cover the trench. One of the Metro river crossings in Prague is done like that.

As for longevity - it is not that different from normal tunnels. Those also need to be often heavily waterproofed due to groundwater (under quite some pressure if you are tunneling under a lot of mountains!) and various underground springs you might tunnel into. So even "regular" tunnels that are blasted or bored often first have to fill the stabilized cavity with hydro-izolation and then actually build the actual hermeticaly sealed tunnel tube inside that out of concrete.

So the segments are allowed to fill with water, and then at the end it is all pumped out ? Or is each segment wrapped in plastic when it is dropped into place, and then they are somehow linked together without the plastic causing problems ?

I watched a couple videos, and neither explicitly stated whether the tunnels are filled with air or water when dropped. Maybe some marketing jerk put a blanket prohibition on any intimation of water in the segments. Bad vibes and all that.

2 year old 30 minutes documentary about it: https://www.youtube.com/watch?v=QiYvXKQksgI

Regular official small update videos: https://www.youtube.com/@FemernAS/videos

It's interesting how they build the concrete parts and then "just" sink them :D

I was wondering why they stopped publishing videos in 2024. They haven't, they switched to Vimeo: https://vimeo.com/1053667887 Here's the last video I could find, showing the first full-length elements floating in the basin in front of the factory: https://vimeo.com/1053667887

I hope it's not vulnerable to anchor drag 'accidents'.

Of course it isn't, it is a tunnel not a cable. That said it could be vulnerable to 'Nord Stream 2' type actions given that it is built using prefab tunnel sections which are sunk down and connected. It would not take that much of a breach to flood the tunnel and make it unusable.

Afaik unlike Nord stream the tunnel sections will be burried in a trench, under a lot of both rock ballast (so they don't float back up) and soil. Not impossible to breach of course, but requiring either a lot of some very serious military grade explosives (earthquake bombs, just underwater, somehow) or a very auspicious drilling rig.

Depending on how much ballast is dumped on top of the segments a number of depth charges detonated on top of the thing might be enough, especially if detonated around the interface between two segments. If a depth charge is not deemed to be effective enough I'd imagine a container full of AnFo would suffice. I also assume the designers have thought about these possibilities, especially after the Nordstream 2 debacle and have taken care to make the design able to withstand such threats.

If this is the route I think it is (Copenhagen to Hamburg), I rode a train on that route about ~8 years ago. It was memorable for the fact that the train itself pulled onto a ferry boat. Pretty cool as a tourist, but I can obviously see how a tunnel would save a ton of time.

The ferry was cancelled a few years ago: the train route is now east all the way across Denmark to Kolding, then south all the way down to Hamburg.

Slightly more info with pictures on the official site: https://femern.com/the-construction/building-the-tunnel/

I still think the https://en.wikipedia.org/wiki/Gedser%E2%80%93Rostock_bridge would have been the better alternative.

„The Danish Social Liberal Party and the Danish People's Party said on 3 June 2007 that they favoured the Gedser–Rostock bridge. They were supported by traffic researchers and a consultant from the German Ministry of Traffic.“

> World’s longest road and rail tunnel is being built under the Baltic Sea

> The tunnel, which will be 18 kilometers long

> By way of comparison, the 50-kilometer Channel Tunnel linking England and France, completed in 1993...

Am I missing something? 50 > 18

Channel Tunnel is rail only; 'road and rail' probably used here to mean both means of transport.

yeah - iirc the concern was that car drivers would be too unpredictable / bored driving 21 miles in a tunnel - so you just drive your car onto a train

And said train is a tunnel too, you can just drive though it. Even has two levels in the car segment (not the truck one obviously). It's really cool.

yeah - I recommend having an overheight car (eg roof box) - then you get to ride in the high ceilinged carriage used by large passenger vehicles such as busses ... no extra cost, very roomy sense of space and smooth motion

btw trucks (as opposed to passanger carrying busses and coaches) are unhitched and take different trains with the drivers all in a dedicated people carriage next to the loco - guess they must have known about truck fires and separation of people from goods

Also, it could cause messy accidents that are hard to reach. I think it was a good choice, if you see what happened in other long road tunnels: https://www.theguardian.com/world/2001/oct/26/jonhenley1

The Chunnel had a train fire once but it was not as bad.

I've been through the Austrian Arlberg Road Tunnel a couple of times, which is just 13km and I was super tired from the hyper focus, as I was leaving it. Can't really imagine doing it for 50km.

The Chunnel is rail only.

I suppose they're being pedantic in that the Channel Tunnel only carries rail traffic.

> […] is one of Europe’s largest infrastructure projects, with a construction budget of over 7 billion euros ($7.1 billion).

the berlin airport was more costly

"... one of..."

the point was a different one: even a "minor" project can be among the most expensive undertakings - and significantly more expensive than this much larger tunnel project - if the germans are involved

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