What is a tunnel boring machine?

A tunnel boring machine breaks through ground material to remove it, forming a tunnel in the process with concrete segment rings.


At Hinkley Point C...

There will be three large tunnel boring machines and one smaller tunnelling kit that will be operating at Hinkley Point C.

The three largest machines will be forming the two intake tunnels, which will supply 120,000 litres of water per second, and one outfall tunnel for the power station's cooling water system. The other smaller kit will be excavating a tunnel to form the fish return system. 

How does the tunnel boring machine operate?

With its rotating cutting wheel at the front of the machine, the tunnel boring machine breaks materials away from the tunnel face. This earth is then transferred to the belt conveyor system inside the machine. There are a number of hydraulic arms which push the machine forward continually using the previous constructed concrete tunnel ring as its platform. 


What are concrete segment rings?

6,000 concrete segment rings will form the walls of the three tunnels. These are created with reinforced segments and grout injected to secure them in place. The segments are being constructed in a state of the art facility at Bristol Port Dock in Avonmouth and the facility will create between 70-100 rings per week (each ring made of 6-8 segments).

Tunnel boring in numbers


tunnellers in each working shift


water intake tunnels


water outfall tunnel


million tonnes of soil to be excavated


months to construct each tunnel


metre shaft excavated to form launch platform

Tunnel boring machine naming and tunnelling history

“Tradition states that the machines have to be officially named before they can start work – and, as the patron saint of miners and tunnellers is Saint Barbara, they are given female names” Gareth Taylor, Project Manager.

A competition was run across the county of Somerset with 215 primary schools invited to enter names of inspirational women of which the machines could be named.

Gareth said: “After much deliberation, our naming committee decided to name the equipment after several prominent women in history.”

The winners are:


Beatrice Shilling 1909 - 1990, was an engineer well regarded by the RAF. Born in Waterlooville she designed the RAE Restrictor (also known as the Tilly orifice) to prevent Merlin engines in Hurricane and Spitfire fighter jets cutting out during nosedives. Beatrice was awarded an OBE in 1947 for her work.

Beatrice was chosen by Cannington Church of England Primary School, Year 5 Beech Class.


Born in Bristol, Lady Emmeline Pethick-Lawrence was a women’s rights activist. Alongside her husband, Frederick Pethick-Lawrence, she fought tirelessly for the right to vote.

Emmeline was chosen by Stogursey Church of England Primary School, Year 5.


World-renowned fossil dealer, collector and palaeontologist, Mary Anning became known for important finds in Jurassic marine fossil beds in the cliffs along the English Channel. She was born and lived in Lyme Regis.

Mary was chosen by St Peter's Church of England First School in Williton.


For the smaller tunnelling kit.

The kit will be called Sarah, after English inventor Sarah Guppy, who worked with Isambard Kingdom Brunel on the design of the Clifton Suspension Bridge.

Sarah was chosen by -Stogursey Church of England Primary School, Year 5.

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