HS2 Colne Valley east - Copthall Green Tunnel

As London bound trains depart the Colne Valley viaduct, a 880m tunnel awaits. Then an embankment, overbridge over Breakspear Road South, followed by another overbridge over the river Pinn. The line will then approach the London north tunnel portal at West Ruislip taking trains to Old Oak Common station.
2 ventilation shafts constructed above the tunnel. There will be 5 shafts in total. The eastern end of the tunnel is still under construction, base slab looks complete(?). Due to be finished early 2025
HS2 is the UK's newest high speed railway linking London to Birmingham and the north. Trains are due to cross the colne valley area here in the early 2030's.

[@simoncroft9792]

Interesting video, not seen much south of the big viaduct

[@stevetony6876]

A lot of what has been created here in the last 18 months or so is now below ground! 👍

[@SIMONC256]

Hello✋, ooh aah those white blocks at 1:32 , insulation? i thought they had finished the first one, its getting bigger,larger and more massive , when will it end , thanks for the update..

[@stevetony6876]

I’m not sure! It’s all very exciting isn’t it… and those muck spreaders.. what a job they have on their hands..epic!!! 👍👍

[@DaveFiggley]

Ha, for me it's that lonely little wheelbarrow that steals the scene. It just looks a little lost amidst all the mega-bucks Tonka toys.

[@DaveFiggley]

Nice one, QM. Why do they need so many airholes on such a short stretch of tunnel? There are the same number, four, along the whole 10 mile length of the main Chiltern Tunnel. Keep 'em coming 👍

[@stevetony6876]

Thanks... yet there are none (if i'm not mistaken) on the 1.5km Long Itchington Wood tunnels up in warwickshire...! 5 does seem a bit excessive on a relatively short length of tunnel.

[@martinsloman6905]

I think they will be for pressure relief - like the 'porous portals' they have on the Chiltern Tunnel. High speed train tunnels - such as the one at Long Itchington have to be very big to prevent a large build-up of air pressure in front of a train. Having frequent vents allows the air to escape meaning the tunnel can be smaller. Another thing to consider is that this is a double track tunnel - unlike most HS2 tunnels that are two single line. Two trains passing each other at high speed create very high air pressure.

[@DaveFiggley]

@@martinsloman6905 Porous portals? Are those the cross-shafts which connect one tunnel to the other?

[@martinsloman6905]

@@DaveFiggley No, they are short extensions at each end of the tunnel with openings in them. The idea is that the pressure pulse from trains leaving the tunnel is reduced so avoiding a 'sonic boom'.

[@DaveFiggley]

@@martinsloman6905 OK, thanks. I'm still none the wiser as to why there are air pressure release breathers every two miles in the Chiltern Tunnel (albeit with some balancing through the cross tunnels) yet Copthall has five(?) blowholes in the space of 880 metres. I appreciate what you're alluding to concerning the 'silencers' at each end of the Chiltern Tunnel and also that trains will be passing each other in the Copthall Tunnel.

[@howardjones6752]

Why is this tunnel being built ? It seems a rather extravagant bit of engineering to me, just to hide a railway.

[@stevetony6876]

It does rather doesn’t it. I checked the alignment and it’s 20m deep so not sure if that’s too much for a cutting or not. Perhaps there was a desire to put something back to the environment because of the viaduct..

[@xwaltranx]

Seems like a still photo.

[@ionardlegras]

Burying the railway in a cut-and-cover tunnel to protect a... car park and warehouse? One of many examples where NIMBYs and over-cautious design mean massive cost increases on HS2.

[@stevetony6876]

It’s an interesting comment frequently asked and I don’t know the answer! Thanks for watching. 👍

[@franekkimonowy9412]

HS2 - R.I.P

[@stevetony6876]

I know HS2 is not for everyone. Thanks for watching. 👍