HS2’s two tunnel boring machines heading northwards out of London have now reached Amersham, passing 5 and a half miles of their 10 mile drive under the Chilterns.
Chiltern tunnel with crosspassageway visible to the right (c) HS2
The two tunnel boring machines (TMBs) have now spent almost two years excavating the twin tunnels running under the Chilterns between the M25 and South Heath in Buckinghamshire.
Each machine is a 170m long self-contained underground factory, digging the tunnel, lining it with 56,000 concrete segments to form rings and grouting them into place as it moves forward. Designed specifically for the geology of the Chilterns, the first TBMs were launched in Summer 2021 from a site near the M25 and have excavated more than 1.8 million cubic metres of chalk and flint.
As well as digging and lining the tunnels, engineers have also completed the excavation of five shafts that will provide ventilation and emergency access near Chalfont St Peter, Chalfont St Giles, Amersham, Little Missenden and an intervention shaft at Chesham Road.
Amersham vent shaft construction – January 2023 (c) HS2
The 44m deep shaft at Amersham – which the TBMs have now passed – will be in the middle of a road junction just outside the Buckinghamshire town. A ‘headhouse’ will be built on top of the shaft to house safety equipment, with a flint-faced boundary wall and a pre-patinated zinc roof to help match the natural tones of the surrounding landscape.
Martyn Noak, HS2’s Head of Tunnel Engineering, said: “I’ve been very impressed with the progress made by Florence and Cecilia as they make their way unseen beneath the Chiltern Hills. It’s great to see how much progress they and the teams excavating the five shafts have made and I’d like to thank everyone involved in getting us this far.”
Amersham vent shaft construction showing internal work (c) HS2
The two TBMs are operated by, Align – a joint venture formed of Bouygues Travaux Publics, Sir Robert McAlpine, and VolkerFitzpatrick.
Each machine has a crew of 17 people, working in shifts and supported by over 100 people on the surface, managing the logistics and maintaining the smooth progress of the tunnelling operation.
Approximately 2.7 million cubic metres of material – mostly chalk and flint – will be excavated during the construction of the tunnels and used for landscaping. Once construction is complete, the temporary buildings at the south portal will be removed and the site landscaped with around 90 hectares of new wildlife-rich chalk grassland habitats. Chalk grassland used to be widespread across the hills of southeast England and are considered habitat of international conservation significance with just 700ha left across the Chilterns.
HS2 currently has five TBMs in the ground, with a further five due to be launched over the coming years. Together they will create 64 miles of tunnel between London and the West Midlands including major tunnels on the approach to London and Birmingham.
We need more tunnels; not just for trains but also for cars. The south-east is so congested, it is a wonder anyone wants to live here. I would also like to see a tunnel dug for a train from Piccadilly train station in Manchester to Victoria station and beyond. Amazing that our second city does not have an underground when cities like Munich and Frankfurt in Germany have extensive underground networks.
Third* city. Birmingham is our second city in terms of population.
Not sure what benefit – if any – a tunnel between Piccadilly and Victoria would bring. Let alone the cost which could be used for so many other more beneficial schemes.
There is a good tram service already between the two which also has intermediate stops which a train wouldn’t do. Well it could but the cost / benefit wouldn’t work out.
There is also a less frequent rail service.
Plus there is also the free bus service between the two.
Lower Thames crossing needed more than ever.
“The government is set to announce that construction of certain sections of HS2 will be delayed in an attempt to cut costs, the BBC understands.”
I’m not aware that delaying a project has ever ‘cut costs’.
My inference from that statement is that HS2 will be completed from OOC to Birmingham Curzon St. but everything else will be put on hold, possibly indefininately.
What started as a grand and exciting plan to link directly the major cities of the North with Birmingham, London and, possibly, the high speed lines of Europe is destined to be whittled down to a new 100 mile stretch of railway between Englands first and second cities.
So much for ‘levelling up’.
Why is this country so inept when it comes to major infrastructure projects?
Ian, no doubt, will trot out his usual mantra that ‘any part of HS2 completed will free up capacity on existing mainlines’.
What a shambles.
Having said all that, the viaduct over the North Orbital is rather spectacular.
What’s wrong with everyone ? Don’t they want to get to Birmingham 20 minutes faster?
Massive white elephant! Will be millions over budget, not starting from central London but Ealing west London finishing at Birmingham… does anyone believe that the Birmingham to Manchester part will ever be built?
That’s the part that should have been built first!
In today’s world the country would be better served with national ultra high speed internet allowing more remote working and entrepreneurial opportunities
I have never been a fan and believe that the whole HS2 project is a waste of public money and was just a big ticket item that was politically expedient post Covid to get people back to work in a large engineering project
Unless you know something about covid that the rest of us don’t – how would a project that was under construction before the pandemic be a “big ticket item that was politically expedient post Covid to get people back to work”?
A cursory glance at Google Earth suggests there was preliminary HS2-related works at the Chiltern south portal site as far back as April 2013 – almost seven years before anyone had heard of Covid.
Er, having had another look, it appears the 2013 activity was to do with a new privately-owned quarry. It helps if you turn on ‘labels’ etc!
The first, definitely indentifiable, HS2 work appears in March 2017 to the west of Tilehouse Lane and the north of the A412.
I should get a life, shouldn’t I?
Er, south of Tilehouse Lane and west of the A412, obviously. I had beer for lunch and the map was skew-whiff.