HS2 Construction - Greatworth and Chipping Warden Green Tunnel

[@frasermitchell9183]

Of all the tunnels, the Chipping Warden tunnel is completely unnecessary. It runs beneath an old airfield used for commercial storage of motorvehicles. There is to be another Cut & Cover" tunnel near Greatworth. All this unnecessary tunneling has piled costs into HS2 along with other "gold plating" thus making it unaffordable with the result the sections north of Birmingham have now been cancelled. The tunnel north from Old Oak Common is also unnecessarily long, ,because there is unused formation by the existing railway.

[@masekwm]

It is crazy isn't considering what is already there, I'm not sure what is being protected by adding the tunnel in CW?

[@DavidKnowles0]

all because Cameron was a cowardly leader.

[@martinsloman6905]

You need to look at the plans and sections on the Gov.UK website to understand why this tunnel is being constructed. The airfield is at an elevation about 23m above the proposed track level due to a local rise in the ground. That would mean a very deep cutting extending some 50m outside the line of the railway. (You couldn't raise the track locally because of vertical alignment constraints). I think use of the term 'green tunnel' may be inappropriate here. Certainly, the tunnel will be cut and cover but the reason for building is more for topographical reasons than to preserve the landscape. Why is a TBM not used? - probably due to the relatively short length of tunnel and maybe due to ground conditions. It seems that at the south end of the tunnel, where it is at shallower depth it bevomes more like a conventional 'green tunnel'.

[@ScottishDroner]

Another good one for the hostory book in years to come

[@SeanDavies-u5t]

Any plans to do another video of this area soon? I’d be interested to see if the road is taking shape and if they started to cover any of the segments yet

[@masekwm]

Unlikely in next few weeks, there had been so little changes between the two videos I did, but if I read of significant changes I'll head up.

[@simoncroft9792]

Another HS2 site where progress seems painfully slow. Reasons for which we will never know.

[@martinsloman6905]

This was the first of the 'green tunnels'. It was started in 2022 and planned to be completed 2 years later. This was where some quality control issues arose with the initial precast sections. I think that may have led to the delay. The tunnel is 2.5km long and they are obviously progressing it. Given the depth of parts of the tunnel, backfilling will be an interesting operation.

[@stephenfoster7257]

Maybe a civil engineer can answer a question for me....If infilled ground gets more waterlogged on one side of the tunnel than the other will there be a syphon engineered in to equalise the water table?

[@martinsloman6905]

I'm just guessing but it looks like this tunnel is well above the water table as the cutting isn't flooding. This type of tunnel construction doesn't seem very waterproof. Generally, tunnels that are below the water table have their joints caulked.

[@TrevorWilliams-fq8mg]

And if the tunnel was in or below the water table dewatering an excavation of this length would cost a fortune. It would require a secant piled retaining wall built both sides of the trench for the entire length. A secant piled wall consists of piles drilled into the sides of each other to form a water resistant barrier, not watertight but enough to reduce water ingress to a seepage which can then be locally pumped out. They are used on basements built next to rivers.

[@deauvilledad07]

Strange way of doing things, would have thought you'd have put the, track down and built the tunnel over it, but what do I know 🤔

[@martinsloman6905]

Tracklaying is one of the last operations. Having the track laid ahead of the tunnel works would obstruct the construction operation and risk damage to the track. Tracklaying in tunnels is not that difficult.

[@deauvilledad07]

@@martinsloman6905 oh, OK 🤔

[@davidstringer4474]

Might be scrapped tomorrow,