Fehmarnbelt construction

[StephenHunter]

Why has this tunnel being put in a massive trench at the bottom of the sea rather than TBMs being used like the Channel Tunnel?

 

[JohnofWessex]

Geology?

 

[Sir Felix Pole]

Geology?

Yes it is a shallow sea with substantial glacial deposits on the bed, so it is easier and cheaper to dig a trench for the tunnel segments.

 

[bluenoxid]

Also consider that “bored tunnels” will desirably be deeper than a cut and cover in the seabed (dredged trench) because boring a tunnel and keeping it water tight is a challenge the closer you are to a water source.

This makes approaches either side more challenging as the trains need more distance to drop to a deeper depth.

An example would be the Tyne Tunnels. The older tunnel is deeper and has a cork screw on the north side. Newer tunnel is shorter.

 

[AlastairFraser]

Also consider that “bored tunnels” will desirably be deeper than a cut and cover in the seabed (dredged trench) because boring a tunnel and keeping it water tight is a challenge the closer you are to a water source.

This makes approaches either side more challenging as the trains need more distance to drop to a deeper depth.

An example would be the Tyne Tunnels. The older tunnel is deeper and has a cork screw on the north side. Newer tunnel is shorter.

Indeed, it's apparently approximately 10.9 miles long and the Channel Tunnel is 31.35 miles long.

 

[HSTEd]

Why has this tunnel being put in a massive trench at the bottom of the sea rather than TBMs being used like the Channel Tunnel?

If the water is shallow enough, you can build a tunnel with a cross section that you could not dream of in a bored tunnel.

Even the largest tunnel boring machine mooted has a tunnel cross section under 300 square metres.
And that's constrained to a 19m diameter circle.

The Fehmarn Belt tunne structure is ~45m wide and 13.1m high (~590 square metres), with a shape much more amenable to fitting vehicles through (ie. rectangular).

If the Chunnel was built today it would probably also be an immersed tube, but immersed tubes were not as developed as they are today at the time.

 

[Snow1964]

Why has this tunnel being put in a massive trench at the bottom of the sea rather than TBMs being used like the Channel Tunnel?

The area is silt and glacial deposits. Would have to go long way down to find suitable material to bore through.

the cut and cover elements have 5 rectangular tunnels. (2 single track rail, 2 road and a service tunnel, so more efficient to build them as wide rectangular shape.

I believe there are 89 tunnel elements, of which 10 also have a lower basement level for equipment eg pumps. The segments are cast as 9 blocks each about 24m long to make segments that are massive 217m long.

Tunnel will be about 19.3km including the sections that will be under the land to portals. Denmark has completely closed the old rail line to Rodbyhavn, from Nykoping Falster, and is rebuilding it as double track, eliminating all level crossings and electrifying the line

For a while the Germans were dithering over widening a road bridge at Southern end of Fehman island so might have been bit of single carriageway road and single track on German approach side. But now building a new tunnel (2 track railway and dual carriageway) to bypass the old arch bridge which will then become a local road and a cycle / pedestrian walkway. I understand rail line has already been removed from the bridge as route is closed for upgrade.

Germany is building a new 200km/h (124mph) double track electrified railway from Lubeck to the tunnel, about 30km is rebuilt existing lines and about 55km new alignment. Due to open in 3-4 years time.

 

[U-Bahnfreund]

Germany is building a new 200km/h (124mph) double track electrified railway from Lubeck to the tunnel, about 30km is rebuilt existing lines and about 55km new alignment. Due to open in 3-4 years time.

As discussed in this thread, most of the German part of the route doesn't have planning approval, let alone construction start, some sections aren't even applied for yet. I wouldn't believe any opening date of 2030 or earlier

 

[Gloster]

As discussed in this thread, most of the German part of the route doesn't have planning approval, let alone construction start, some sections aren't even applied for yet. I wouldn't believe any opening date of 2030 or earlier

I have just had an e-mail from someone I know who is well informed about this and he says that opening of the link has been delayed until 2032 for road traffic and shortly after that for rail traffic. So maybe they will complete the line in Germany in time, you never know!

 

[StephenHunter]

I have just had an e-mail from someone I know who is well informed about this and he says that opening of the link has been delayed until 2032 for road traffic and shortly after that for rail traffic. So maybe they will complete the line in Germany in time, you never know!

This is Germany. The reputed efficiency, if it ever truly existed, died long ago.