Four million tons of clay moved in HS2 excavation

The digging machines used on the project are being removed

Four giant tunnelling machines working below west London have completed the excavation of the 8.4-mile (13.5km) Northolt tunnel between West Ruislip and a new station at Old Oak Common as part of the HS2 project.

The Tunnel Boring Machines (TBM) excavated more than four million tonnes of London Clay and installed almost 100,000 concrete segments to form the tunnel walls, according to HS2.

Now engineers have begun the process of lifting the last of the four machines used on the project to the surface.

The first part of TBM, "Anne", saw the light of day for the first time in 16 months as it was lifted out of a shaft at Green Park Way in Greenford, west London, on Sunday.

The machine weighs 1,700 tonnes and was removed in sections

Anne is named after Lady Anne Byron, an educational reformer and philanthropist who established the Ealing Grove School in 1834, England's first co-operative school.

The machine weighs 1,700 tonnes and stretches for around 490ft (150m), including the 30ft (9.11m) diameter cutter head.

Construction on HS2's second-longest tunnel started in October 2022.

The rotating cutters cut away clay and other material at a rate of about 50ft (15m) a day, with a crew of 17 people operating each machine in shifts covering 24 hours a day.

The TBMs launched from the West Ruislip and Old Oak Common sites met in the middle and completed the Northolt tunnel in June.

HS2 said the millions of tons of clay it has dug up have been disposed of at "designated sustainable disposal sites and rail freight hubs to minimise road transport, where the material can be reused for beneficial purposes or returned to the local landscape".

The excavated material is transported by conveyor belts from the TBMs to railheads and then taken by train to logistics hubs, such as the one at Willesden Euro Terminal, for onward rail transport to locations across the UK.

Multibillion-pound overspend

Work is ongoing to build the final 4.5 mile (7.2km) of tunnels from Old Oak Common to Euston station in central London.

The completion of the Birmingham to London high-speed rail project was put in doubt in October 2023 when the then-prime minister, Rishi Sunak, said extending the project from Old Oak Common to Euston would be reliant on private investment.

However, in her Budget in October 2024 the Chancellor Rachel Reeves committed to the funding required to begin tunnelling work to Euston.

In 2009, when the government announced the new high-speed line to link the capital with regional cities, it was predicted the London to Birmingham section would be completed by 2020 and cost £7bn.

That phase of HS2 is now expected to open between 2029 and 2033.

The Department for Transport said the remaining project cost was estimated at £45bn to £54bn in 2019 prices, however, HS2 management estimated £49bn to £57bn.