Well, the concrete for the tunnel lining would involve a lot of CO2 emissions.
I also don't know whether the cost could be justified on any rationale.
That's a political issue, not a technical one. If a government sees a benefit, whether its benefits are quantified or not, it can decide to shoulder an investment. But, even though I don't think that the Irish Sea Tunnel would cost more with today's technologies than the Chunnel did with technologies back then, it looks like a tall order.
maximum sea depth of c. 100M
At a length of 90+km, the real challenge is not depth. It is length, and water control. Unless one or more expensive articical islands/giant caissons are built in the sea for intermediate accesses, it would have to be bored from both ends, meaning the transport of dug material away from and tunnel lining towards the TBM over up to 50 km. Building watertight tunnels across water-bearing strata is no problem per se, but you should better know in advance what rocks can be expected in sequence, so a lot of boreholes would have to be dug between Dublin and Holyhead.
bridge option - which could be enclosed to avoid weather issues - although snow on Irish sea is v. rare and slight and I presume wind is not a problem for trains
Enclosed: costs even more, you just lifted the tunnel above the sea, and added pylons. And wind is a problem for any vehicle with significant side wall surface area.
I repeat that bridges aren't a cheaper alternative. The reason Denmark built its two big sea strait crossing links as bridge-tunnel combinations was on one hand to avoid complications with ventillation for the road tunnel part, on the other hand to keep bridge-building experts employed. (And the same reasons apply for the planned Fehmarn Belt crossing.)
bridge pillars doubling as turbine pylons
That's not necessarily a good idea. Vibrations, danger to trains if a blade breaks or sheds ice. *Lunatic*, n. One whose delusions are out of fashion.
As you say - cost is ultimately a Government decision, but I would see it as v. likely to be totally unaffordable for any Irish Government in the foreseeable future especially when the cost of upgrading rail infrastructures on both sides of the sea are taken into account.
Are there any general studies/macro-comparisons available of the relative CO2 emissions of building and operating rail networks (with large tunnel components) compared to other modes of mass transportation? notes from no w here
As you say - cost is ultimately a Government decision, but I would see it as v. likely to be totally unaffordable for any Irish Government in the foreseeable future
There is the current budget crisis; but, you never know what governments are willing to waste money on. In the diary, I presented an example, the Koralmbahn: that little-justified project will cost the Austrian government €5.25 billion, while 3-4 other investments of a similar scale are on-going. (I estimate the Irish Sea Tunnel at €10-15 billion; for scale: the geologically much more difficult Gotthard Base Tunnel will cost around SFR9.7 billion = €6.5 billion). Another example: here in Hungary, the government maintained the big budget for highway construction even when public deficit exploded a few years back. *Lunatic*, n. One whose delusions are out of fashion.
If by some miracle that level of value is ultimately recovered over the next 10 years we could perhaps do worse that using the proceeds to pay off some of the national debt and invest in some major infrastructural projects which reduces our long term dependence on CO2 intensive transportation. The costs you outline don't seem outlandish, although the government has a track record of mismanaging infrastructural projects to the extent that they come in at two or three times the original budget.
The Chunnel experience is not encouraging. Have tunneling technologies, techniques, and cost factors improved dramatically since? No doubt prevailing ideologies would require some PPP type funding architecture which would require a huge risk premium to attract private investment. notes from no w here
OTOH, if its portside, that means that one time advantage of trucks is offset by doing ship loading/unloading directly from/onto the train.
So a grid of "Steel Interstate" model corridors that all end at a port would seem to be the most promising basic model.
If the the passenger trains are going at least 175kph, its hard to see why they'd have to go faster.
If only the standard gauge turn-outs have to be high speed turn-outs, it seems like it'd be possible to dual-gauge the track in intermediate stretches and switch out to a dedicated standard gauge section for crossing and passing loops and stretches with a larger number of turn-outs per km. Common right rail if the typical standard gauge passing loop is passing to the right. I've been accused of being a Marxist, yet while Harpo's my favourite, it's Groucho I'm always quoting. Odd, that.
