It’s certainly not every day that a boring machine the height of two double decker buses breaks through at the end of HS2’s longest tunnel – a pivotal moment for Britain’s biggest infrastructure programme. The pages of many of national papers were filled the following day with stunning images of the enormous steel cutterhead emerging into the daylight. The image was even captured in BBC News’s week in pictures.
But what about the other machines? How many are there, and where are they all?
The short answer is ‘10’ but, as ever, the long answer is slightly more complicated…
In terms of context, HS2 will have 32 miles of tunnel between London and Birmingham, of which the Chilterns is the longest at 10 miles.
All of those tunnels are ‘twin bore’ with separate tunnels for northbound and southbound trains, and so a few hundred metres behind Florence and due to breakthrough alongside her in a few weeks is her twin, Cecilia. In fact, if you count each bore separately, our TBMs will complete an incredible 64 miles of tunnelling compared with 26 miles on Crossrail.
In London, the tunnels are being dug by six more machines. Of these, three (Emily, Sushila and Caroline) are already at work between Old Oak Common and West Ruislip, while another (Anne) is preparing to launch. These machines are slightly different to the Chilterns TBMs – while the Chiltern machines mix the chalk with water to form a slurry which is them pumped out of the tunnel, the London machines use a conveyor belt to move the London clay out of the tunnel.
Two further TBMs (as yet unnamed) will be used to dig the Euston tunnels. These are currently being manufactured and tested before they are delivered to site, ready to dig the last 4.5 miles to HS2’s ultimate London terminus.
A slightly smaller reconditioned Crossrail machine, named Lydia, was used to dig the short Atlas Road logistics tunnel from the Old Oak Common station box to a rail logistics hub at Willesden. This will allow engineers to bring in tunnel segments and remove spoil from the Euston tunnels without getting in the way of work on the main Old Oak Common station site.
In the midlands, Dorothy dug the first half of the relatively short Long Itchington Wood tunnel, before being turned around and sent back to complete the twin bore in March 2023.
She’s now been reconditioned, renamed Mary Ann, and is now at work on the Bromford tunnel on the approach to central Birmingham. She was joined by another TBM this week, named Elizabeth, and together they will excavate the 3.5 mile tunnels.
So, if you only count TBMs digging the running tunnels for HS2 trains, and exclude mini-TBMs like ‘Lizzie’ digging utility tunnels, there’s 10…
If you count the Atlas Road logistics tunnel, there’s 11….
And if you count a reconditioned TBM with a new name (Dorothy/Mary Ann) as a new TBM, there’s 12.
However you count them, TBMs are fascinating pieces of equipment and you can find out more about them elsewhere on our website and via take a tour through one of our youtube videos.
