Giant machines digging HS2’s longest tunnel have passed the halfway point, according to the firm building the high-speed railway.
HS2 Ltd said the pair of tunnel-boring machines (TBMs) have each made five miles of progress on their 10-mile journeys under the Chiltern Hills.
Once completed, the twin-bore tunnel will be used by high-speed trains travelling to and from London.
The 170-metre-long machines, named Florence and Cecilia, are working continuously, operating as self-contained factories.
More than 1.3 million cubic metres of chalk and flint, enough to fill 500 Olympic-sized swimming pools, has been excavated.
It will be used as part of a chalk grassland restoration project at the south portal of the tunnel near Denham, Buckinghamshire alongside the M25 motorway.
Florence was launched there in May.
She was named by local schoolchildren after Florence Nightingale, the founder of modern nursing who spent many years in the county.
Cecilia, named after Buckinghamshire-born astronomer and astrophysicist Cecilia Payne-Gaposchkin, began digging two months later.
HS2 Ltd’s head of tunnel engineering Martyn Noak said: “It’s great to be able to celebrate the halfway point of this 10-mile long tunnel.
“The whole team has put in a fantastic effort over the last year and a half, and I’d like to congratulate the crews of both Florence and Cecilia for passing this important tunnelling milestone and thank them for all their hard work
“This tunnel will take HS2 underneath the Chiltern Hills, safeguarding the woodlands and wildlife habits above ground as well as significantly reducing disruption to communities during construction and operation.
“Once complete, HS2 will offer low carbon journey options linking London with the major cities of the North and releasing capacity for more freight and local trains on our existing mainlines.”
A total of 10 TBMs will be deployed between London and the West Midlands for Phase One of the high-speed railway.
Chancellor Jeremy Hunt said last week he did not see “any conceivable circumstances” in which HS2 would not run to its planned central London terminus at Euston, amid reports that section of the route could be axed because of rising costs.