Bridges v Tunnels.

Varies quite a bit with the individual situation.

Not necessarily, particularly where the bridge is over a very large drop and the tunnel is in where it is easy to tunnel.

Mostly, but not always.

Again, it depends on how the bridge is done.

Again, that depends on how the bridge is done.

Again, it depends on the nature of the under water ground.

The devil is in the detail. For the Oresund, there is a bridge and a tunnel for different parts of the crossing.

For Holyhead to Dublin to make sense you would also need to get rid of the bottleneck at the Menai Straits. Quite apart from trying to decide where to put the Customs point.

And the tunnel. I watched a documentary a few moths back where in they built concrete tunnel sections o land, floated them out to the location where they were sunk and joined and then pumped out.

On 13 Apr 2022, alan_m wrote

Not sure if this is the one that was about, but that method was used in San Francisco in the 1960s for the BART (Bay Area Rapid Transit) line. (I remember it since it was still a novel approach when I did my town planning degree in the mid 1970s, which makes me feel kind of old; I guess that's because I am......)

This is from

The Bay Area Rapid Transit District asked a Bechtel joint venture to develop engineering data, a preliminary design, and estimates for a radically new rapid-transit system. The plans were approved in 1962 and the joint venture was given the green light to perform detailed engineering and manage construction.

The project team constructed the 3.6-mile- (5.8-kilometer-) long underwater passage in 57 sections. Fabricated above ground, the concrete-and-steel modules were floated into place, immersed—with their ends sealed into a trench spanning the bottom of San Francisco Bay, between San Francisco and Oakland. Crews made watertight connections between the sections, removed the end caps, and secured the entire tube.

The BART project's most dramatic feat, the Transbay Tube, a submerged tube across San Francisco Bay, was completed in 1969. The project also included a hard-rock tunnel through the Berkeley hills.

(unquote)

Those adverse conditions can affect the road or railway on a bridge as well, Norway being a country prone to snow using a tunnel keeps the link clear of snow,Ice and wind that could disrupt it.

Proposed in Spring last year with a bit of a fanfare by Boris and Co and then dropped quietly in the Autumn when having likely paid some friends ,sorry Consultants a load of dosh to confirm what people had said for free in the first place that it would cost to much to justify. The traffic isn?t really there to pay on the investment and is less now that many more ferry routes have opened direct between Ireland and the Continent since Brexit to avoid the hassle of going across the land bridge route across a non member state. For some thats a loss of trade servicing the trucks and drivers and less traffic for the English Channel Ferries. On the balance it less wear and tear on UK highways ,fewer emissions and fewer trucks to get stuck behind.

GH

Isn't there a deep trench between Britain and Ireland allegedly filled with dumped munitions?

Also, didn't one plan use the Isle of Man as a roundabout?

Blue sky thinking at its best.

Cheers

Dave R

alan_m has brought this to us :

In the USA?

David laid this down on his screen :

Yep, WWII surplus munitions were dumped there.

Also done in Wales (A55 at Conway/Conwy), but not until the 1990s.

The bridge and tunnel that links Denmark to Sweden is done that way I believe, because the sea is shallow and they simply laid a tube on the sea bed, more or less which had no impact on sea traffic at all. In the bits too shallow for navigation its just a causeway on posts so to speak.

That's how the North Wales Expressway gets under the River Conwy estuary

I think the Norwegians have a sense of national pride in their tunnelling skills. The impression I formed was that they're all blasted and they sneer at TBMs. There's a car park in Bergen - it may not be unusual - but it's underground, IIRC seven stories deep, and in rock.

Mind you, they have loadsa money.

The last time we were in Amsterdam, they were building carv park UNDER one of the canals

Currently the nearest one is just off junction 9 of the M56, so that's, err, great.

Yeah, fascinating, that one. Big flexible teflon seals or something. Had to take seismic activity into account. I'll explore that link, thanks.

This is what got me thinking about it - they have the money to tunnel so perhaps it's a cheaper in the long run.

But not a tunnel. That is where millions of tons of ordnance was dumped after 1945. And I believe it is rather tougher material then that nice easy chalk marl that the Chunnel went through.