Initial photos have been released of the building site where HS2 tunnels will dive under the M25 and tunnel their way beneath the Chilterns towards Birmingham.

Excavation site – the M25 is towards the top of the photo (c) HS2

The South Portal Chalfont Lane site will be the biggest construction site on the project. From here, one team will launch the tunnels northwards, while another heads towards London on the adjacent Colne Valley Viaduct.

Around 350 staff from HS2’s main works contractor, Align JV are on site now, and at its peak, around 1200 people are expected to be employed in the design and construction of the Chiltern tunnels and the viaduct.
The new images show the excavation of the launch site and the start of work to build the concrete precast plant where more than 118,000 tunnel segments will be made.

A concrete wall is needed to stabilise the excavated site and give the tunnel boring machines a ring to hook into when they start digging. The TBMs need to start this deep down as they need a certain amount of soil above them to be able to start tunnelling.

Stabilisation wall with TBM launch eyes in the concrete (c) HS2

Two tunnel boring machines – currently being manufactured in Germany – will dig the 10-mile-long Chiltern tunnels and will launch from this site just inside the M25 motoroway, not far from Gerards Cross. The ‘twin bore’ Chiltern tunnels will be the longest and deepest tunnel bores on route, with separate northbound and southbound tunnels and five ventilation shafts.

Material excavated from the tunnels will be reused as landscaping on site.

Post-construction landscaping concept (c) HS2

Just to the south of the tunnel portal, the Colne Valley Viaduct – designed by Align, working with its design partners Jacobs and Ingerop-Rendel, and the architect Grimshaw – will be the longest railway viaduct in the UK. At 3.4km long, it will carry HS2 across the Grand Union Canal and surrounding lakes.

Further south, the line will go into tunnel again before arriving at Old Oak Common and London Euston.


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  1. Adam Edwards says:

    Great to see this happening. Reminds me of the Channel Tunnel at Calais when the site was being made ready.

  2. Nigel Headley says:

    The A3 hindhead road tunnel site was exactly like this. Stabilisation wall looked the same although there was no TBM in Surrey. The soft sandstone was dug out

  3. Richard Durell says:

    this complete waste of money should be stopped right now before anymore money is wasted on it. this money is neede for far more important things –especially after the virus outbreak.

  4. Alan Barton says:

    I live nearby. The site is enormous and has wrecked a big slice of countryside. HS2 not too bothered about their impact. They have closed Chalfont Lane for 8 years. Also the bridleway at 5 & 10 in the picture – quite unnecessarily and without providing any diversion. I doubt if they will be able to use all the 13 million tons of spoil to reshape landscape – much will have to be taken elsewhere.

    • ianvisits says:

      The large slice of countryside that was wreaked being a few fairly bland empty fields.

      And frankly, it happens to all building sites – in cities, towns, and yes, shock, in the countryside — and like city and town building sites, they are eventually ex-building sites and made good again.

      People need to look at the bigger picture, and be less NIMBY about short-term disruption and look to how the site will be restored, and, based on the planning documents, arguably be much nicer afterwards.

    • James E Fletcher says:

      I hope commenters like these never travel on any motorways or any railways, otherwise they’re just NIMBY hypocrites.
      A railway consumes far less land and has less impact on the environment than motorways per passenger kilometer. Motorways have a constant drone, tyre particle pollution & fossil fuel emissions.

  5. ANdy McDougall says:

    The waste of money some people are complaining about is not HS2 itself but 10 miles of completely unnecessary tunnelling to pacify the Buckinghamshire nimbys.

    • A Hope says:

      Those Nimby’s should be deported to where I live – Runcorn. The cramped housing and chemical plants are gorgeous.

  6. Bob Robertson says:

    I, too, live within 5 or 6 miles of this site and know, or knew, that stretch of Chalfont Lane like the back of my hand. It’s a shame the lower part of this ancient thoroughfare has been changed forever but, having said that, the M25 had already sliced through it several decades before – in the eighties we used to ride our motorcycles up and onto the groundworks. I was, vehemently, anti-HS2 and still think parts of the scheme, especially the lack of a direct through route from HS1, don’t make sense but it is obviously going ahead and on a grand scale. My scepticism has been allayed slightly after viewing this fly-through from HS2/Arup:

  7. Robin leederp says:

    This so called waste of money will be here far into the future long after those moaning about it are long gone the victorians who built so many great things must look done on us in dismay!we need new infrastructure not people standing in the way of progress and we need work that projects like this create.its very hard to do anything in this country without certain people making it fuss over it let’s just get on with it.its happening get.over it

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