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Old March 4th, 2017, 10:48 PM   #101
Amexpat
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Originally Posted by Silly_Walks View Post
Where do you get this 92 km number?
From the Railway Gazette article cited a number of posts above:
http://www.railwaygazette.com/news/n...missioned.html

Last edited by Amexpat; March 5th, 2017 at 09:48 AM.
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Old March 5th, 2017, 12:13 AM   #102
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From the Railway Gazette article sited a number of posts above:
http://www.railwaygazette.com/news/n...missioned.html
I get nowhere near that number when measuring on a variety of maps, along some very sensible routes.
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Old March 5th, 2017, 01:16 AM   #103
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I get nowhere near that number when measuring on a variety of maps, along some very sensible routes.
That struck me as long as well. I checked online and found 82 km as the distance between Helsinki and Tallinn.
http://www.mapcrow.info/Distance_bet...allinn_EN.html

However, the water looks to be between 60-80 meters deep between the two cities (see p. 99 of link below), so it would take some distance for a rail tunnel to get above sea level on both sides (rail tunnels, especially HSR, can't have as steep a gradient as a road tunnel)
http://www.borenv.net/BER/pdfs/ber3/ber3-097-125.pdf
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Old March 5th, 2017, 05:10 AM   #104
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When will this be completed?
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Old March 5th, 2017, 09:26 AM   #105
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Quote:
Originally Posted by Amexpat View Post
That struck me as long as well. I checked online and found 82 km as the distance between Helsinki and Tallinn.
http://www.mapcrow.info/Distance_bet...allinn_EN.html
Note how far is it diagonally across Finnish Gulf. Shouldnīt a sensible route go on land to Porkkala peninsula and then cross under Gulf along a shorter route?
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Old March 5th, 2017, 10:21 AM   #106
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How do you arrive at the construction would cost 1/10 of most of other tunnels?
The thing here is that about 75% of the whole length it will be in Granite. This is also the reason why there is already in place a tunnel over 100km in finland.
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Old March 5th, 2017, 10:22 AM   #107
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It seems that it's hard to find overground space in Helsinki for the corridor, due to this reason it seems that the most reasonable variant will be to put it under the city and because of this reason maybe it isn't so favorable any more to bring the line back up for a while in Porkkala.
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Old March 5th, 2017, 10:57 AM   #108
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The thing here is that about 75% of the whole length it will be in Granite. This is also the reason why there is already in place a tunnel over 100km in finland.
Solid granite is better than varying rock, but you still need TBM's for the tunnels and it's not 1/10th the cost of other tunnels.

Finland does have the second longest tunnel in the world at 120km, but it's a water tunnel, which is something different. Any rail connection would need three tunnels to be built, two rail in each direction and a service tunnel. All three would have to have expensive equipment in place and interconnecting ducts and passages for air pressure and fire safety.

A water tunnel would be about the size of the service tunnel and is fairly simple to build and maintain. No escape routes , no rail tracts, no electricity, no fire safety needed, etc.
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Old March 5th, 2017, 12:19 PM   #109
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The Gotthard Base Tunnel doesn't have a service tunnel, although it does have cross-passages every 300m.
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Old March 5th, 2017, 12:47 PM   #110
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The Gotthard Base Tunnel doesn't have a service tunnel, although it does have cross-passages every 300m.
True, but it does have three access tunnels, two of which lead to a combined technical and rescue station. It also has an air shaft somewhere near the middle. I don't think you could have access tunnels or an air shaft for a sea tunnel.

Last edited by Amexpat; March 6th, 2017 at 06:14 AM.
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Old March 5th, 2017, 01:03 PM   #111
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Solid granite is better than varying rock, but you still need TBM's for the tunnels and it's not 1/10th the cost of other tunnels.
Maybe not so much cheaper, but even if it is two times cheaper then it's also a huge benefit. 1/10th per unit I have heard from a source quite a long ago, and yes things tend to change over time... Yes 15 years ago only a few people could think about Tallinn - Helsinki 30min link, now a lot of us know and feel that it should be already reality.
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Old March 6th, 2017, 02:30 PM   #112
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I don't get the 92 km distance either. The normal ferry route looks to be about 85km but if I was to build a tunnel I would start at the island just past Puunsi which could be reached by bridge, tunnel towards Jarvo and bring it ashore on bridges an causeways. This would require about 55 km of tunnel
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Old March 6th, 2017, 04:47 PM   #113
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I don't get the 92 km distance either. The normal ferry route looks to be about 85km but if I was to build a tunnel I would start at the island just past Puunsi which could be reached by bridge, tunnel towards Jarvo and bring it ashore on bridges an causeways. This would require about 55 km of tunnel
You still would need some kilometers on both sides to get above sea level with the gentle gradient needed for HSR and freight. The Channel tunnel, for example, is 50 km long with 38 km undersea. So even if it was feasible to have the tunnel at the narrowest point of the Gulf of Finland, the tunnel would still have to be at least around 65 km in total. Of course there might be reasons why they can't have the tunnel at the narrowest point.
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Old March 6th, 2017, 07:41 PM   #114
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The depth of the channel tunnel and where it reaches the surface is controlled by the geology and the topography of the region.

It follows the chalk marl layer and the 9km inland after shakespeare cliff are more to do with with this and the cliffs. It is only 35m below the seabed at the French coast and 45m below on the UK side, hardly depths that require Kms of tunneling to produce an acceptable gradient.
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Old March 17th, 2017, 11:22 AM   #115
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Lately Helsingin Sanomat published an article about the geology and possibilities for Tallinn - Helsinki railway tunnel.

It states that the geology mainly being of granite and also blue clay is the most favorable for tunneling works.

Using TBM-s it is possible to make it in 5 years.
Using conventional methods it would take 15 years.

Due to favorable ground levels in the sea it is possible to create two islands for ventilation/equipment transport shafts.

An informative illustration is added to the statement.

http://www.hs.fi/tiede/art-2000005120355.html
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