Should HS2 be a very long tunnel?

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Ianno87

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And do people who aren't enthusiasts really care?
They care about getting to their destination quickly and with the minimum of fuss.

If it was all in a tunnel they would be closer to doing so as construction on Phase 1 would have started years ago.
Would it? Tunnels still require the same planning consents, particularly:
-The impact of ventilation shafts/emergency tunnel access
-Tunnel construction/excavated material removal by road or rail
 
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Silent

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Most railway lines these days are largely a monotony of tree covered trackside these days.
And 99% of passengers don't really care what is outside of their window these days.
I prefer continuous greenland to continuous tunnel anyday. Too much tunnel makes me feel a bit claustrophobic.
 

HSTEd

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Would it? Tunnels still require the same planning consents, particularly:
-The impact of ventilation shafts/emergency tunnel access
-Tunnel construction/excavated material removal by road or rail
Ventilation shafts for rail tunnels are considerably less impactful than those for road tunnels for obvious reasons, after all the air being ventilated is not heavily contaminated with various nasties produced by internal combustion engines.

Even then you can fit ventilation shaft tops inside a fake barn or similar buildings.
There would be effectively no blight near the tunnels or whatever - which would reduce the effective length of line that NIMBYs would complain about from the current length to a few kilometres total of tunnel breaks for fire access reasons.
Construction spoil would still be an issue but the terrain being moved through is hardly barren, there are canals and railways available for the transport of spoil if lorries are not acceptable for political reasons.
And spoil production is inherently more concentrated than in surface line construction and is thus easier to deal with without lorries.

Remove the NIMBYs and the project would have started construction by now.
 

Ianno87

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Ventilation shafts for rail tunnels are considerably less impactful than those for road tunnels for obvious reasons, after all the air being ventilated is not heavily contaminated with various nasties produced by internal combustion engines.

Even then you can fit ventilation shaft tops inside a fake barn or similar buildings.
There would be effectively no blight near the tunnels or whatever - which would reduce the effective length of line that NIMBYs would complain about from the current length to a few kilometres total of tunnel breaks for fire access reasons.
Construction spoil would still be an issue but the terrain being moved through is hardly barren, there are canals and railways available for the transport of spoil if lorries are not acceptable for political reasons.
And spoil production is inherently more concentrated than in surface line construction and is thus easier to deal with without lorries.

Remove the NIMBYs and the project would have started construction by now.
No, it *still requires exactly the same consents process to be gone through*. Ergo no quicker to get a Hybrid Bill.

And then take longer to build a tunnel once that's all gone through...
 

HSTEd

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No, it *still requires exactly the same consents process to be gone through*. Ergo no quicker to get a Hybrid Bill.

And then take longer to build a tunnel once that's all gone through...
Would we be waiting for ridiculous numbers of NIMBY petitions to cycle through the consultation process and dealing with endless legal challenges by the likes of StopHS2? I doubt it.
 

najaB

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Would we be waiting for ridiculous numbers of NIMBY petitions to cycle through the consultation process and dealing with endless legal challenges by the likes of StopHS2? I doubt it.
Probably. They would just find something else to raise objections about. I'm guessing that damage to the water table would be high up the list.
 

HSTEd

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Probably. They would just find something else to raise objections about. I'm guessing that damage to the water table would be high up the list.
Thats a niche environmental complaint - that is nothing compared to the kind of difficulties made by people who will end up with HS2 within sight of their house ;)
 

Mojo

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No - it is simply personnel observations over large numbers of rail journeys.
I'm not so convinced myself, but if this was the case I'd imagine a large proportion of these customers will be requiring some sort of mobile connectivity, something which obviously by default is not available underground.

Given the lengths of tunnels and cuttings on HS2, are there proposals to install Wifi on board the trains that works underground, or install something in the tunnels that gives 4G/mobile phone reception?
 

edwin_m

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I'm not so convinced myself, but if this was the case I'd imagine a large proportion of these customers will be requiring some sort of mobile connectivity, something which obviously by default is not available underground.

Given the lengths of tunnels and cuttings on HS2, are there proposals to install Wifi on board the trains that works underground, or install something in the tunnels that gives 4G/mobile phone reception?
I don't suppose it's been decided yet, but as all trains on the network are supposed to have free wifi within a few years, no doubt HS2 will have whatever the current technology is at the time.

If the Channel Tunnel can have mobile access then I'm sure it's possible on the shorter and more accessible tunnels of HS2.
 

po8crg

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They would mostly be complaining about the construction sites and the amount of road traffic on them. Since many of the complaints are about that, I doubt you'd save much time.
 

HSTEd

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They would mostly be complaining about the construction sites and the amount of road traffic on them. Since many of the complaints are about that, I doubt you'd save much time.
With a tunnel there are only a handful of point construction sites, not one enormous long one.
 
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edwin_m

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With a tunnel there are only a handful of point construction sites, not one enormous long one.
There is more road traffic though, because the amount of new material to come in and spoil to go out will be much greater. Even though a deep cutting will create more spoil than a tunnel of the same length, it is usually possible to move this only a short distance to use as fill for a nearby embankment.
 

snowball

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Even though a deep cutting will create more spoil than a tunnel of the same length, it is usually possible to move this only a short distance to use as fill for a nearby embankment.
Nowadays often including a pair of embankments forming a "false cutting" for environmental screening.
 

HSTEd

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There is more road traffic though, because the amount of new material to come in and spoil to go out will be much greater. Even though a deep cutting will create more spoil than a tunnel of the same length, it is usually possible to move this only a short distance to use as fill for a nearby embankment.
However careful selection of your TBM launching points allows the spoil to be moved out along a major transport artery - for example you woudl launch a TBM near an existing motorway junction or where railway access can be provided. This minimises the effect of the extra spoil moves even though much more tonne-kilometers is required to complete the task.

The chilterns are hardly an undeveloped desert after all.
 

snowball

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Yes but this discussion arose in the context of a suggestion to put the whole route in tunnel. The problem would then be many times greater.
 

The Decapod

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HS2 originally boasted 'futureproof' design for speeds of up to 250 mph. I don't know if that's still the case or whether it's been watered down. Given that the Channel Tunnel has a limit of about 100 mph for safety and operational reasons, any bits of HS2 that are in tunnels are likely to have a speed limit considerably less than the overall governing line speed. So the more of HS2 that's in tunnels, the longer the overall journey times.
 
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MarkyT

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HS2 originally boasted 'futureproof' design for speeds of up to 250 mph. I don't know if that's still the case or whether it's been watered down. Given that the Channel Tunnel has a limit of about 100 mph for safety and operational reasons, any bits of HS2 that are in tunnels are likely to have a speed limit considerably less than the overall governing line speed. So the more of HS2 that's in tunnels, the longer the overall journey times.
In the the Channel Tunnel example, speed of the fastest trains is limited primarily to maintain total capacity for the whole traffic mix, dominated as it is by the slower car and lorry shuttles. There is s similar policy in force in the new Alptransit tunnels in Switzerland, where passenger trains are not permitted to travel at their top speed along these very busy mixed traffic routes. While very high speed is possible in tunnels, cross sectional area of the bores has to be increased significantly to accomodate it. There's a trade off point at which the additional tunnelling costs outweigh the potential business benefit of further speed increases.
 

The Ham

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In the the Channel Tunnel example, speed of the fastest trains is limited primarily to maintain total capacity for the whole traffic mix, dominated as it is by the slower car and lorry shuttles. There is s similar policy in force in the new Alptransit tunnels in Switzerland, where passenger trains are not permitted to travel at their top speed along these very busy mixed traffic routes. While very high speed is possible in tunnels, cross sectional area of the bores has to be increased significantly to accomodate it. There's a trade off point at which the additional tunnelling costs outweigh the potential business benefit of further speed increases.
I would also argue that with much of the HS2 tunneling being cut and cover the extra costs with a larger tunnel (required to allow the higher speeds) would mostly be associated with the removal of the extra soil and a small uplift in the tunnel section costs.

It also depends on if the trains run in a single large tunnel of two smaller tunnels. If a single tunnel, then for much of the time there wouldn't be a train heading in the opposite direction and so there is a lot of space for the air to get off the way, and even when there were two trains it would only have very limited impact on the speed of the trains and the associated air pressure.
 

HSTEd

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HS2 originally boasted 'futureproof' design for speeds of up to 250 mph. I don't know if that's still the case or whether it's been watered down. Given that the Channel Tunnel has a limit of about 100 mph for safety and operational reasons, any bits of HS2 that are in tunnels are likely to have a speed limit considerably less than the overall governing line speed. So the more of HS2 that's in tunnels, the longer the overall journey times.
The primary reason for the 100mph limit is to prevent the Eurostars being so much faster than the Shuttles that tunnel capacity falls through the floor as the Eurostars end up running on notional yellows behind them.

This does not really apply in HS2's case since the tunnels will be built largely for the ruling linespeed.
 

HSTEd

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Hyperloop has lower capacity, has not been shown to actually work and has numerous technical problems that each justify a thread of their own. If we were not going for standard guage high speed rail the next best choice would likely be either some form of maglev (like the Chūō Shinkansen technology) or something totally off the wall like a high speed Breitspurbahn.
 
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DPWH

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I would also argue that with much of the HS2 tunneling being cut and cover the extra costs with a larger tunnel (required to allow the higher speeds) would mostly be associated with the removal of the extra soil and a small uplift in the tunnel section costs.

It also depends on if the trains run in a single large tunnel of two smaller tunnels. If a single tunnel, then for much of the time there wouldn't be a train heading in the opposite direction and so there is a lot of space for the air to get off the way, and even when there were two trains it would only have very limited impact on the speed of the trains and the associated air pressure.
Cut and cover tunnels are all fine and fair for flat land as found in cities built on floodplains, but most of the country isn't particularly flat, meaning that for a long distance line to going through hills would require very large cuttings to be infilled afterwards, or using methods other than cut-and-cover for construction, or somehow building a railway on an embankment, then building a bigger embankment to give sides to a "tunnel".

Meanwhile, those parts of the country that are flat tend to have water tables just below the lie of the land, so any cut and cover tunnel is going to get rather wet and probably require pumping.

Basically, the suggestion is entirely ridiculous. But then Donald Trump is president-elect, so who knows?
 

HSTEd

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Cut and cover tunnels are all fine and fair for flat land as found in cities built on floodplains, but most of the country isn't particularly flat, meaning that for a long distance line to going through hills would require very large cuttings to be infilled afterwards, or using methods other than cut-and-cover for construction, or somehow building a railway on an embankment, then building a bigger embankment to give sides to a "tunnel".
Earth moving is enormously cheap - so any location where there are no major disruption costs from the excavation and where the tunnel is less than something like a hundred metres deep will be cheaper to build using a cut and cover tunnel technique.

And it is worth noting that since HSR can tolerate major gradients you can follow the lie of the land - this is not a freight line that needs to remain flat. We can have indefinite gradients as steep or steeper than the Lickey.
 

Trog

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If you were to dig a cutting a 100m deep without putting in two huge and vastly expensive retaining walls first to hold up the sides during the excavations, to get a safe slope on the cutting sides while you work the cutting would be about a quarter of a mile across. That means moving about 34,000 tons of earth for each metre run of the cutting.
 
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HSTEd

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If you were to dig a cutting a 100m deep without putting in two huge and vastly expensive retaining walls first to hold up the sides during the excavations, to get a safe slope on the cutting sides while you work the cutting would be about a quarter of a mile across. That means moving about 34,000 tons of earth for each metre run of the cutting.
And that doesn't actually cost that much any more - especially since long term spoil disposal is not an issue since almost all of it will go straight back into the hole afterwards. And at lower depths (since the tunnel is unlikely to be a continuous 100m below ground level) the amount of earth to be moved shrinks rather drastically.
 

edwin_m

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And that doesn't actually cost that much any more - especially since long term spoil disposal is not an issue since almost all of it will go straight back into the hole afterwards. And at lower depths (since the tunnel is unlikely to be a continuous 100m below ground level) the amount of earth to be moved shrinks rather drastically.
A surface railway is sometimes below and sometimes above grade, depending on the local topography. The design usually aims to balance the cuttings and embankments as far as possible, so the spoil from the cuttings roughly balances the amount needed for the embankments.

If it has to be in tunnel then by definition it can't go above grade, so where the ground goes from low to high, to stay underground in the low part it will be that much deeper underground in the high part so the amount of spoil to be removed and put back will be more than the amount to be removed (only) on a surface railway.

The entire length will also require concrete lining segments to be brought in, and after filling in the trench there will be spoil left over equivalent to the volume of the tunnel plus the lining. As there are no embankments to use this up, it will have to be disposed of off-route. All this will add up to maybe a dozen HGV movements in and out of the site for each metre of tunnel.

For this and other reasons, a cut and cover tunnel will involve far more disruption to the locals during construction than a normal surface railway would. There may be less noise and disruption after completion, but evidence from HS1 indicates that it's reasonably straightforward to mitigate the noise impacts of operational high speed trains.
 

HSTEd

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It doesn't necessarily have to be disposed of off site in open country.
You can just leave the ground level higher than it was before the tunnel was constructed.
 

edwin_m

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It doesn't necessarily have to be disposed of off site in open country.
You can just leave the ground level higher than it was before the tunnel was constructed.
Sort of giant linear molehill? Locals will love you for that!

Isn't the sole vague point of the idea to put the whole of HS2 in tunnel that it would leave the existing environment undisturbed?
 

HSTEd

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Sort of giant linear molehill? Locals will love you for that!

Isn't the sole vague point of the idea to put the whole of HS2 in tunnel that it would leave the existing environment undisturbed?
Considering the cutting is much wider than the tunnel segments dropped into the hole, and the tunnel cross section is inevitably much smaller than the cut is - the extra height is probably going to be rather small.

If the cutting really ends up 100m+ wide then a ~150 square metre tunnel ends up with a 'mole-hill' just over a metre tall.
It leaves the environment undisturbed in that a slight bump in the landscape will dissapear in short order.
 
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