How many tunnel boring machines does it take to start work on HS2?

Posted by Derek Mason

19th January 2021

Photo credit: Herrenknecht AG

If there were any lingering doubts as to whether HS2 is going ahead, they can almost certainly be laid to rest now that Skanska, Costain and STRABAG has signed off on contracts for London’s first two tunnel boring machines (TBMs).

For those of us fascinated by engineering and construction, whatever we think about HS2, it will be interesting to see the work unfold.

The boring machines will be designed and manufactured especially for the London clay and chalk they need to be able to bore through. The German manufacturing company, Herrenknecht, which specialises in tunnelling equipment and technology, will build these TBMs and they should arrive at West Ruislip by the end of this year. They will be some of the most technologically advanced boring machines in the world.

Once launched, these two boring machines will travel 5 miles east to create the western section of the Northolt Tunnel. When the TBMs get to Green Park Way in Greenford, they will be removed from the ground and that site will become a vent shaft.

All in all, there will be 10 separate boring machines, working two at a time to create twin tunnels covering 13 miles for the London HS2 tunnels and 64 miles in total between London and Birmingham.

The London boring machines will begin their tunnel drive in the middle of 2022 and keep going – only breaking for Christmas Day and bank holidays – until the start of 2024.

Tunnels will begin outside Euston station, and continue to Old Oak Common in West London – an overground train station. They’ll then head back underground until they reach West Ruislip in West London.

Two of the ten machines have already been built – those are the TBMs needed to construct the tunnels through the Chilterns. Perhaps in a bid to win hearts and minds, local school children were asked to name the boring machines. So, as a result, Florence and Cecilia will soon be making their way beneath the English countryside.

The machines weigh in at 2,050 tonnes, which is roughly the same as 380 elephants. They’re 140m in length, just under 10m in diameter and between them they’ll excavate 1.2 million cubic metres of material, weighing 2.46 million tonnes.

With that volume of material to clear, and just under two years budgeted, it’ll be interesting to see whether the tunnels are dug out to schedule, or whether a few delays creep in.

What do you think? Will they be finished boring within that timeframe?

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