[HN Gopher] How the Fehmarnbelt Tunnel is being built
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How the Fehmarnbelt Tunnel is being built
Author : blutack
Score : 71 points
Date : 2022-02-18 10:40 UTC (12 hours ago)
(HTM) web link (www.youtube.com)
(TXT) w3m dump (www.youtube.com)
| dgritsko wrote:
| The 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?
| brnt wrote:
| All tunnels in the Netherlands are built this way. You can't
| drill through mud.
| ghostly_s wrote:
| I 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 wrote:
| The caisson technique is not new.
| BurningFrog wrote:
| I think it's the only way to do it:
| https://en.wikipedia.org/wiki/Immersed_tube#Construction
| asdfman123 wrote:
| It 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.
| mstade wrote:
| To 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 wrote:
| The immersed tube technique is used for the BART Transbay Tube,
| Chesapeake Bay Bridge Tunnel, and Oresund 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.
| baud147258 wrote:
| looking at videos YT is suggesting, which are mostly about
| construction of underwater tunnels, it seems it's common
| earthscienceman wrote:
| There 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?
| barbazoo wrote:
| I remember this project being controversial back in the day. I
| wonder what the locals think of that today. Definitely impressive
| technology.
| rurban wrote:
| The better article on this would be "Why the Fehmarnbelt tunnel
| was not built". Because in Germany you cannot build big public
| projects in time and within budget. First you have politicians
| in the way, interfering in the project, with often absurd
| goals. But even worse, you have competing companies, which
| litigate contracts after the deadline, so you have to wait 10
| years until the courts decided if the contract is valid or not.
| Costs are 10x higher then of course.
|
| In Denmark this project would have been built in a year, in
| time and in budget. But unfortunately this involved Germany, so
| now they have another huge stinking overcost project. Denmark
| is angry
| xcambar wrote:
| Is Denmark really angry?
|
| About construction delays and politicians getting in the way
| etc., I can only think of BER as a catastrophic project. Do
| you have more in mind?
| bar_de wrote:
| Local 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 wrote:
| > 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 wrote:
| Yes 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 wrote:
| I think it has to be looked at from a greater picture. I
| previously lived in Skane 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 Malmo 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.
| mahathu wrote:
| flixbus
| _Microft wrote:
| There was news recently that the environmental survey was not
| done as thoroughly as it should have been and that they were
| building (or planning to build) through areas where actually so
| far undiscovered reefs are. A court awarded an injunction to
| hold work there for now if I recall correctly. I can't image
| that it is that popular.
| phkahler wrote:
| I'm curious about the seals between sections. How they do that?
| jccooper wrote:
| It 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/crawnci...
| mertd wrote:
| and how is the bulkhead removed?
| dghughes wrote:
| Especially s bulkhead that's between two segments that are
| both underwater.
| erentz wrote:
| I'm assuming the bulkhead is secured inside the tube. Once
| complete you enter at the end of the tube (on landside) and
| sequentially go through removing each bulkhead from the
| inside of the tube.
| _dain_ wrote:
| How do they join the tunnel segments to each other? How do they
| properly seal it? The video glosses over that part.
| ggm wrote:
| Grout. 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 wrote:
| They must not be in an earthquake zone. The BART transbay
| tunnel has giant rubber flexible joints between segments.
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