HomeTechnologyHigh-speedDorothy sees daylight as she completes a historic run

Dorothy sees daylight as she completes a historic run


After eight months of being deep underground, Tunnel Boring Machine (TBM) Dorothy has broken into daylight.

She has powered through to create the first out of a total 64 miles of tunnel which will span intermittently between Manchester and London, emerging at Long Itchington Wood late last week.

In total, 130 million tonnes of earth will be excavated by TBMs, enough to fill Wembley Stadium 15 times. Of these, HS2’s Chiltern Tunnel will be 16 km (10 miles) long and run at depths of up to 90 metres, making it the deepest point on the route.

Dorothy is not just an engineering marvel, however, she is an employment powerhouse: Dorothy is one one of ten TBMs that will be deployed on the project and employed about 400 workers.

You can click here to visit a map to see where the tunnel boring machines are in terms of their progress:

Red circled (clockwise from top) are TBMs Dorothy, Florence and Cecilia

 Each TBM comprises thousands of parts including:

  • a rotating cutterhead;
  • a screw conveyor;
  • conveyor belts or extraction pipes;
  • a tunnel segment erector.

These help the TBM carry out its two main functions of digging and lining the tunnel simultaneously.

Giant cutterheads at the front of the TBM rotate, cutting away at the earth. The spoil is then carried up the screw conveyor and out of the TBM within a slurry pipe or on a conveyor belt. On average, each TBM will dig and line up to 15 metres of tunnel a day.

Some stats on the TBMs

  • The TBMs are up to 170m in length.
  • Each one weighs roughly 2,000 tonnes.
  • The size of the largest HS2 TBM cutterhead is 10.26m.
  • The internal diameter of the tunnels in which the trains will pass through will be around 9 metres.
  • The tunnels will be lined with concrete segments that will be 2m x 4m and weigh on average 8.5 tonnes each.
  • 112,000 of these concrete segments will be required to complete both tunnels.
Trudy Harrison MP.

HS2 Minister Trudy Harrison said:  “This is, quite literally, a ground-breaking moment – demonstrating that we are getting on with delivering on our promises and progressing our transformative plans to boost transport, bring communities together and level up the North and Midlands.

“As Dorothy paves the way for journeys between Birmingham and London, we continue to strive towards a greener, faster and more direct transport network. And along with our record breaking Integrated Rail Plan, we’re boosting the economy, delivering over 25,000 jobs.”

The tunnels have been specially designed to protect the ancient woodland and complex ecosystem above. They integrate with the natural landscape by reusing material excavated from the tunnel to build a soil ‘roof’ around the tunnel entrance. The rest of the excavated material will be transported by a conveyor belt out of the site rather than lorries and truck, avoiding the use of around 30,000 HGVs on the local roads.

HS2 will play a key role in the government’s £96 billion Integrated Rail Plan – the biggest ever public investment in Britain’s rail network – which through the creation of three new high-speed lines will add more seats, shorten journey times, support local services and deliver a modern, fully connected transport for the North and Midlands quicker than under any previous plan. 


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