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How the Fehmarnbelt Tunnel is being built [video]
- dgritsko 5y agoThe idea of sealing each section and then floating it into position seems so elegant and simple. Is this a common technique for a project of this style, or a new innovation?
- baud147258 5y agolooking at videos YT is suggesting, which are mostly about construction of underwater tunnels, it seems it's common
- brnt 5y agoAll tunnels in the Netherlands are built this way. You can't drill through mud.
- ghostly_s 5y agoI think OP is referring to using the interior space of the segment for buoyancy rather than hauling it on a barge, not prefabrication in general.
- brnt 5y agoThe caisson technique is not new.
- jamiek88 5y agoIt’s not caisson either. How about understanding the conversation and questions being asked before jumping in with dismissive (incorrect) answers?
- ghostly_s 5y ago? This is not caisson construction.
- brnt 5y agoIt's what the construction consortium writes they are doing [1]. Looks like it too? [1] https://www.betoningenieure.de/dateien/FT2018/Seiten/fehmarn.html https://www.betoningenieure.de/dateien/FT2018/Seiten/fehmarn...
- sitkack 5y agoWhat that shows is the mold that is used to make the tunnel segments. A Caisson is like an upside down boat turned into a diving bell that is used to get access to the seafloor. https://en.wikipedia.org/wiki/Caisson_(engineering) https://en.wikipedia.org/wiki/Caisson_(engineering) Famously used in the construction of the Brooklyn Bridge https://fromthepublicdomain.com/2020/08/26/the-brooklyn-bridge/ https://fromthepublicdomain.com/2020/08/26/the-brooklyn-brid... 10 minute documentary on Brooklyn Bride https://www.youtube.com/watch?v=Ct_-0GC_QfM https://www.youtube.com/watch?v=Ct_-0GC_QfM The Ken Burns' documentary is really worth a watch, https://en.wikipedia.org/wiki/Brooklyn_Bridge_(film) https://en.wikipedia.org/wiki/Brooklyn_Bridge_(film) https://www.pbs.org/kenburns/brooklyn-bridge/ https://www.pbs.org/kenburns/brooklyn-bridge/
- ghostly_s 5y agoI think this might be a translation issue - the German Senkkasten is literally "sinking-box," so maybe it does apply to structures like these segments too? But the English caisson only means the diving-bell things.
- jaclaz 5y agoYes it must be lost in translation somehow, in Italian also "cassone" is both the "diving bell" thingy and the "sinking box". The Mose in Venice (though it is a sort of foldable dam) has inside a tunnel for maintenance and it was built in a similar way: https://www.mosevenezia.eu/cassoni/ https://www.mosevenezia.eu/cassoni/
- BurningFrog 5y agoI think it's the only way to do it: https://en.wikipedia.org/wiki/Immersed_tube#Construction https://en.wikipedia.org/wiki/Immersed_tube#Construction
- asdfman123 5y agoIt can't possibly be new. Multi-billion dollar construction projects are fairly common and that kind of capital investment makes people very clever. Oil rigs definitely follow the prefabrication and then float-into-position approach, and have been doing that for a long time. I'm sure there's a good reason why it's more cost effective or feasible to do this instead of drilling a tunnel under the seabed.
- Taniwha 5y agoNot new - as mentioned above the BART trans-bay tube was built this way back in the '70s
- mstade 5y agoTo your point of this technique not being new: the mulberry harbors the allies built following the d-day invasion of operation overlord made use of prefabricated sections code named phoenix, that were towed into place and then sunk to form the structure of the harbor. They were so named, I think, because after being built they were sunk off the coast of England before being refloated in preparation of the operation, i.e. like the phoenix the rose, or something poetic like that. If you're ever in or around Normandy I highly recommend a visit to the beaches. They're much bigger than I had imagined, and it really hit home then what a massive operation it was. Anyway – no, the technique is not new.
- ianburrell 5y agoThe immersed tube technique is used for the BART Transbay Tube, Chesapeake Bay Bridge Tunnel, and Øresund Bridge Tunnel between Denmark and Sweden. The Fehmarn Belt will be the longest when it opens. I think the technique is mainly used for shallow tunnels in flat areas.
- Someone 5y agoThe scale is different, but it’s far from a new idea. https://en.wikipedia.org/wiki/Immersed_tube#Examples https://en.wikipedia.org/wiki/Immersed_tube#Examples: The first tunnel constructed with this method was the Shirley Gut Siphon, a six-foot sewer main laid in Boston, Massachusetts in 1893. The first example built to carry traffic was the Michigan Central Railway Tunnel constructed in 1910 under the Detroit River, and the first to carry road traffic is the Posey Tube, linking the cities of Alameda and Oakland, California in 1928. The oldest immersed tube in Europe is the Maastunnel in Rotterdam, which opened in 1942.
- barbazoo 5y agoI remember this project being controversial back in the day. I wonder what the locals think of that today. Definitely impressive technology.
- bar_de 5y agoLocal here. We were told to enjoy about 60 additional freight trains per day. The promised noise protection barriers were saved on due to budget after public voting went through. Interestingly the ferry which is currently used to transport trucks is only at roughly half capacity. It is a prestige project and I will have to move to some other place as I live next to the train tracks. These are used very sparingly today and are mostly not even electrified and one-tracked. Many wildlife refuges are on the way to move for the sake of the new tunnel.
- mertd 5y ago> Interestingly the ferry which is currently used to transport trucks is only at roughly half capacity. Sometimes the existing solution doesn't need to be bursting at the seams to justify building something better. A better solution can induce its own demand.
- ed_balls 5y agoYes I imagine most of the traffic goes through the bridge in Denmark. What is more, that bridge is a single point of failure, which is a problem in case of an accident or maintenance.
- Gwypaas 5y agoI think it has to be looked at from a greater picture. I previously lived in Skåne in Sweden, from there I could get to Gothenburg in little over 2 hours and Stockhholm in like 4 and a half, with the slow high speed trains in Sweden running at a maximum of 200 km/h. By distance from Malmö to Hamburg is a bit farther than to Gothenburg and Berlin is a bit closer than Stockholm, with the forced dogleg of going through the Fehmarn Belt. By air it would be like Leipzig. That is how far into Germany you get. It is simply ridiculous that the only way I could think of to get to the larger cities in northern Germany would be to fly. Take the train to Copenhagen airport and likely Ryanair or something similarly awful costing less than the ticket to the airport. Sure I could look up some train travel with a multitude of changes through Denmark, likely taking the train on the ferry. Or an over night sleeper style, if they even run. I know there's been talk of them starting again. It's 2022, there should be high speed links.
- phkahler 5y agoI'm curious about the seals between sections. How they do that?
- mertd 5y agoand how is the bulkhead removed?
- jccooper 5y agoIt seems that they have rubber gaskets on the ends. Once the sections are in place, friction (from the foundations and overburden of that segment and the rest of the tunnel) would hold it in place. There do also seem to be systems that have cables to keep the segments in tension. https://www.penta-ocean.co.jp/english/business/civil/crawnciel.html https://www.penta-ocean.co.jp/english/business/civil/crawnci...
- _dain_ 5y agoHow do they join the tunnel segments to each other? How do they properly seal it? The video glosses over that part.
- ggm 5y agoGrout. Inject grout between the units from a pontoon, ROV or diver to guide. When dry, inside can detach a bulkhead, remove surplus grout from new unit, and remove it's bulkhead in turn. It's shallow water so doesn't need high pressure resisting caulk seals to be mostly watertight. They say 15mm tolerance. You could butt fit rubber or polystyrene foam to keep things mostly OK and.. grout.
- Animats 5y agoThey must not be in an earthquake zone. The BART transbay tunnel has giant rubber flexible joints between segments.
- ggm 5y agoThey probably do have these too. Given time everything moves.
- SideburnsOfDoom 5y ago> They must not be in an earthquake zone It's between Denmark and Germany. You can look it up. No, it isn't in an earthquake zone.
- LargoLasskhyfv 5y agoEarthquakes are overrated. See https://en.wikipedia.org/wiki/Seikan_Tunnel#Maintenance https://en.wikipedia.org/wiki/Seikan_Tunnel#Maintenance
- earthscienceman 5y agoThere are some great questions in here. But what I'm most curious about is how the keep the individual segments from sinking into the seabed at different rates. I can't imagine that the interfaces would remain water tight if any segment sunk by, say, more than 30cm. Can we really be certain about the stability of sediment underwater at the loads that will be applied?
- avianlyric 5y agoLooks like they’re over digging the trench, then partially backfilling with aggregate. So the sections aren’t sat on sediment, but rather a thick bed of gravel type material that will distribute the load over a larger space. I would also be interested to know what the tunnels effective weight will be once it’s submersed. Given the sections are hollow, the road and train sections will create a buoyancy effect. Possibly enough to offset the total weight of the concrete, given they need to fill ballast tanks in-order to sink the sections. If that’s the case, they can probably adjust the ballast tanks to keep the sections near to neutrally buoyant, and thus apply little pressure to the sediment below.
- earthscienceman 5y agoThis makes sense and, although I didn't include it in my comment, the buoyancy was part of my curiosity. While it's clever to take advantage of the buoyancy created by the air cavity, if they're nearly-buoyant that would also mean that the variability in traffic would create a significantly variable (as a percentage) load. I wonder how this is accounted for. For the record, I don't think I'm "gotcha-ing" the engineers by thinking of these questions. I'm sure there have been answer to these questions since before the project began, it's just that I would like to know the answers. They also must have a way to seal off segments in case of a water breach? Although, that seems awful given there will be human traffic in the tunnel
- mattashii 5y agoSee the video for answers: After putting in a segment, the trench is backfilled with rocky material (over the segment), so that any buoyancy is negated by the fact that it's held down by a large layer of rocks. This layer presumably also prevents most, if not all, leaks from generating instant floods in the tunnel. Lastly, once completed the project will result in 5 parallel, but mostly independent tunnels (two train tunnels, two highway tunnels, and a service tunnel between the highway tunnels). I presume that the tunnels can be isolated and waterproofed seperately.
- smm11 5y ago
- dang 5y agoCould you please stop posting unsubstantive comments to Hacker News? You've been doing it a lot, unfortunately, and we've already asked you to stop. https://news.ycombinator.com/newsguidelines.html https://news.ycombinator.com/newsguidelines.html
- systemvoltage 5y agoI was just thinking, when was the last time we did something like this in the US? The California rail project has been going on for years, no one dares to even suggest building something like this. All great bridges were built over 50 years ago. If you suggest to do something major in the Bay Area, you would be booo'ed into oblivion for a mere suggestion.
- mfringel 5y agoYou only have to go back 19 years for the Zakim bridge in Boston. https://en.wikipedia.org/wiki/Leonard_P._Zakim_Bunker_Hill_Memorial_Bridge https://en.wikipedia.org/wiki/Leonard_P._Zakim_Bunker_Hill_M...
- alksjdalkj 5y agoIn the NYC area off the top of my head there's been the Tappan Zee bridge, the East Side Access project bringing the Long Island Rail Road into Grand Central Terminal, and 2nd Ave Subway Phase 2. Penn Station Access is being discussed, as is the Triboro RX line. ETA: If you're curious NYC has a dashboard of capital projects >$25 million here: https://www1.nyc.gov/site/capitalprojects/dashboard/dashboard.page https://www1.nyc.gov/site/capitalprojects/dashboard/dashboar.... I think the complaint that we don't build anything in this country anymore is sometimes overstated.
- bobthepanda 5y agoESA and 2nd Ave Subway Phase 2 are kind of the poster children of what's wrong with American infrastructure projects. ESA was started in 2006 and planned to be finished in 2009 at the cost of $4.3B. It is now projected to be finished in 2023, at a cost of $12B. Phase 2 of SAS costs $6B despite the fact that most of the tunnel actually already exists, and won't open until possibly 2029. It's not even really about saving money to save money, but the high costs of these projects suck money away from other projects and needs. It's basically unfathomable at these prices for NYC to do something like Paris and build out 200 km (124 mi) of metro in the next decade.
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- wrnr 5y agoVery cool, In Norway they are considering creating a floating tunnel that is held up with giant floating bois tederet to the ground because some places the sea is just to deep and steep. Anyway here is a video, dunno about current status: https://youtu.be/Gt1MDQHLjF8?t=26 https://youtu.be/Gt1MDQHLjF8?t=26
- andrew_ 5y agoThis would almost certainly require some advanced sea traffic mitigation. See the Sunshine Skyway Bridge Tragedy [1]. Even with openings for vessels, there's a real threat by large vessels. [1] https://en.m.wikipedia.org/wiki/Sunshine_Skyway_Bridge https://en.m.wikipedia.org/wiki/Sunshine_Skyway_Bridge
- CRConrad 5y ago> there's a real threat by large vessels. Which is a bit weird: Why have those pontoons on the surface in the first place? They could provide just as much buoyancy if they were tethered just above the tunnel itself, at a depth of some tens of meters. Or below it, pushing upwards in stead of pulling. (This would also avoid any potential problems with ice dragging them sideways in the winter.)
- waiseristy 5y agoCould probably turn that production facility into a lucrative business if those tunnel segments could be transported down the coast / into the Mediterranean.
- ghostly_s 5y agoConcrete is ALWAYS produced locally, unless there is a very good reason not to. Shipping it is not cheap.
- dan-robertson 5y agoConversely so many buildings are made out of blockwork, and I don’t know if those concrete blocks are manufactured particularly locally.
- ghostly_s 5y agoThey almost always come from a foundry within 200-500 miles, yes.
- waiseristy 5y agoThat's shipped via road though isn't it? Barging would be immensely cheaper for long distances
- pvg 5y agoprecast and otherwise pre-fabricated concrete has been in use for about as long as there's been concrete.
- ghostly_s 5y agoSure - and it's generally sourced from the closest concrete foundry possible, unless there is something exceptional about the design of the units which make that impossible. When I researched this in undergrad ~2006 90+ % of all concrete was sourced within 300 or 400 miles, iirc.
- dillondoyle 5y agoHow much time does this actually save? Just looking at the crude map it doesn't like like a huge amount? Like slightly more than cutting a rectangle into a hypotenuse (idk the term, like cut into triangle, the new long edge, still shorter than the other two combined) VERY cool though
- jacobr 5y agoTrain from Copenhagen to Hamburg goes from 4.5 to 2.5 hours. As a Swede, this makes vacations to the continent via car or train much more attractive.
- dillondoyle 5y agoThat sounds really nice! I wish we had train network in the US. Though I get the country is huge but so is Europe from tip to tip.
- LargoLasskhyfv 5y agoYou do. It's just not used for PAX, besides a few exceptions. Look for Class 1 Railroad on Wikipedia, and compare freight to passenger trackage.
- abliefern 5y agoThe new train line is going to be 160km shorter while also allowing higher speeds. Trains between Hamburg and Copenhagen are projected to take less than 2:30h, down from 4:40h today.
- dillondoyle 5y agoThat's pretty good. Especially if it saves energy on trains. but the cost is HUGE for 2 hours.
- ant6n 5y agoIt's 2 hours times the number of passages through the tunnel. Hint: there will be more than a single passage. Jokes aside, there are sometimes rail projects where millions are spent to save 2 minutes. Or even just tens of seconds. Over the lifetime of the infrastructure it is still worth it, especially when combining multiple projects. 2 hours savings is huge. You won't find many infra projects with those kind of time savings.
- shawn-butler 5y ago2 million+ tons of emitted CO2 mostly from the Portland concrete elements.[0] We really need to find some low-carbon alternatives that are structurally and economically feasible. Hope it's worth it. [0]: [pdf] https://vvmdokumentation.femern.dk/39.%20E6TR02217843.pdf?filename=files/BR/39.%20E6TR0221.pdf https://vvmdokumentation.femern.dk/39.%20E6TR02217843.pdf?fi...
- SECProto 5y agoAt $200/tonne (a reasonable minimum price that we should be paying for CO2 emissions), you'd be looking at $400 million budget increase on a project with a budget roughly 8.5 billion USD 7 years ago [1]. It wouldn't make or break the project. If we want people to start taking CO2 into consideration when designing projects, it needs to have a cost associated with it. Ideally that cost should be used to offset the CO2 emitted. It wouldn't solve any issue but it will incentivize solutions that use less CO2. [1] https://femern.com/finance/ https://femern.com/finance/
- rootusrootus 5y agoWhen it's the government doing the building, where is the money going to actually go? Are there readily available carbon capture facilities operating right now at commercial scale?
- SECProto 5y ago400 million would fund a lot of emissions reductions (obvious ones like improving residential/commercial efficiency with insulation, adding more renewable energy, and less obvious ones like improved grid interties, etc). CCS is not real yet (though if there was $200/t on the table, it would be more likely to come around). The real positive impact it would have though is incentivizing lower carbon development: if traditional concrete has unpriced carbon emissions, there's no incentive for a design to specify using a low carbon alternative that might cost slightly more.
- xyzzyz 5y ago$200/tonne is far above "reasonable minimum price" for CO2 emissions. Average estimate is closer to $50/tonne. At $200/tonne, you're entering "viable air capture of CO2" territory.
- papaver-somnamb 5y agoHave rising sea levels and storm surges been taken into account for the planning of the entrances? Watching the video, wondering if it is an accurate depiction of size and placement, I couldn't help the bolt of consternation that shot through me, because those entrances look awfully close in elevation to sea level. And regarding air management, in Japan and HK at least, driving through lengthy tunnels can already be a stinky affair, especially in summer, so ensure your vehicle's air conditioning system is set to cycle the air inside the car. The Tokyo Bay Aqua Line tunnel that connects Yokohama to Chiba is quite long and it uses large fans that vent at mid-way points, one doubling as a tourist stop. The Fehmarnbelt tunnel being the longest in the world is therefore longer, and I didn't see such venting points. Yes I noted the air movers in the video. But hey, I'm hopeful that such problems will attenuate with electrification.
- wasmitnetzen 5y agoIt's only the longest immersed tunnel, nowhere near the longest overall. It's only 18km. Though the Tokyo Bay Aqua Line tunnel is only 10km long, the Channel Tunnel is 50km, but then again, that one doesn't have car traffic.
- andrew_ 5y agoMy number one question is how they plan to dredge the seabed and keep that surface flat enough for the tunnels to sit on. connecting with millimeter precision would require a flat surface, no? Fascinating.
- HendrikR 5y agoHow exciting this would be to cycle through the tunnel once the tunnel is completed but not yet released to public (car) traffic? Near Hamburg people enjoy riding their bikes on a nearly completed section of a new motorway although it's strictly forbidden.