Should HS2 be a very long tunnel?

[Class 170101]

Don't forget that 270kph is the top speed in HS1 tunnels north of Ebbsfleet. Thats faster than 160kph used in the Channel Tunnel.

 

[dalmahoyhill]

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.

it costs about £1.50 for each cubic metre on large projects. You would never dig a cutting 100m deep. where is the world have you seen one of that size. 30m deep is about the max. safe batter would be 1 in 1.5 to 2. you can work out the quantities from that
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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.

speed is only limited in the tunnel by the wind resistance and the extra energy to overcome it. Shinkansen routes in Japan run predominantly in tunnel and they have 200mph line speeds. However with trains like the N700 see the length of noses required to reduce the piston effect in the tunnels!

So minimising the length of tunnels is good for energy usage. You can go for a larger diameter to reduce the piston effect but again that costs more.

So to the original poster, yes you could put the whole of HS2 into a tunnel but it would cost a bomb and for what end?

 

[snowball]

According to a post on Skyscrapercity, the FT is reporting that the government will confirm the routes for HS2 from Crewe to Manchester and from Birmingham to Leeds tomorrow (Tuesday), including the easterly route past Rotherham.

[Oops - I intended to post this in "HS2 in the press" but put it here by mistake. I've now posted it there too.]

 

[NotATrainspott]

The 230km/h single-bore tunnels in cities will have a 7m diameter and the 400km/h single-bore tunnels (most notably under Crewe) will have a 10m diameter. The pressure wave that builds up at the front of the train is the main reason for the increased tunnel diameter. Unlike most of the European HSR lines, most HS2 tunnels will be single-bore, and many of the mainline cut-and-cover ones will have a central dividing wall between the two tracks.

 

[Trog]

it costs about £1.50 for each cubic metre on large projects. You would never dig a cutting 100m deep. where is the world have you seen one of that size. 30m deep is about the max. safe batter would be 1 in 1.5 to 2. you can work out the quantities from that

I did to show what the implications of a 100m deep cut and cover tunnel would be, as that had been suggested and I thought it was not a sensible option.

The deepest cutting I can think of in the real world is part of the Panama canal at just under 50m.