HS2's first London tunnel reaches one mile

First milestone passed for London’s HS2 tunnelling.

HS2 has announced that the first milestone has been reached in the project to tunnel under London.

The first two Tunnel Boring Machines (TBMs) have completed the first mile, with over 847 tunnel rings being installed each since launch in November 2022. The TBMs are tunnelling in opposite directions, as Sushila constructs the “downline” section that will host trains travelling south towards the capital and Caroline works on the “upline” tunnel for services running towards the Midlands and the North.

Tunnelling has seen more than 240,000 cubic metres of mixed soil extracted, with the mixtures of London Clay, chalk and sand being used to create new landscapes and wildlife habitats north of the tunnel. Once the project is completed, the Northolt Tunnel will be 8.4 miles long and expectations are that it will be finished by 2025.

Huw Merriman, Rail Minister, said:

“As the construction of HS2 continues to develop at pace, we edge closer to the benefits of this transformational railway coming to life.

“While its construction protects natural habitats and creates thousands of jobs, its completion will soon connect our largest cities and create quick, sustainable rail journeys that are fit for the future.”

Dair Meadow Primary School in Southall named the first TBM, deciding to name it after Sushila Hirani. Hirani is a local teacher who has a passion for increasing the numbers of girls and pupils from BAME backgrounds in STEM. The second TBM was named by Brentside Primary Academy School, after astronomer Caroline Herschell.

HS2’s Main Works Civils Contractor, Skanska Costain STRABAG joint venture, has committed a team of 17 tunnel engineers to operate each TBM, with the team working in partnership with a ground team that is 60 people strong.

Managing director of Skanska Costain STRABAG JV, James Richardson, added:

“Completing our first mile of tunnelling on both of our TBMs is a fantastic moment for the HS2 London tunnels programme. Early next year, our two TBMs will be launched from Victoria Road crossover box, close to Old Oak Common station. All these drives will then meet at Greenpark Way in Greenford, forming the route for the initial opening of HS2 into London.

“The HS2 London tunnels team is undertaking some of the most complex tunnelling operations ever embarked on and this milestone has been achieved through a combined effort of all parts of the team. Shafts along the route are all now reaching completion of the civil engineering works in preparedness for the TBMs to pass underneath. We’ve also embarked on one of the largest utility projects to enable the tunnels to safely pass through this year.”

This section of the tunnels will require 58,000 tunnel segments, with these being manufactured on Kent’s Isle of Grain by Pacadar. These have recently been delivered by rail to the sidings at the West Ruislip site, to reduce the number of lorry journeys required.

Touching on the progress of the tunnelling under London, HS2 Project Client Malcolm Codling, said:

“Work to build the HS2 network in London is gaining momentum and completing one mile of twin bored tunnel is another sign of progress on delivering the HS2 route between London and Birmingham.

“HS2 will deliver zero-carbon journeys from day one, linking the major cities of the Midlands and North with London and releasing train path capacity for local, regional and freight services.”

The team are now beginning preparations for the start of the construction of cross passages between the two tunnels, with these being used in emergencies.

Autumn 2023 is when the TBMs are expected to reach the first ventilation and emergency access shaft at South Ruislip, which will be once they have covered 1.7 miles. This shaft is 35 metres deep, with a ‘headhouse’ being built above to house safety equipment. The roof of the building will be green and will be constructed of brick and timber that is sympathetic to the local landscape.

To complete the 8.4-mile-long tunnel, two more TBMs will be launched at the opposite end, from the Victoria Crossover Box in Ealing, next winter. The four TBMs will then end their journeys at Greenpark Way in Greenford, which will then see them extracted from the ground.


Image credit: HS2


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