The first mile of the two HS2 tunnels running under west London from Ruislip towards Old Oak Common has been completed, and is on target for the tunnels to be completed by 2025.
The HS2 railway runs in tunnels from Euston to the station at Old Oak Common, and then in tunnels roughly parallel with the Central line up to Ruislip, where the trains will then run over the lakes on a long viaduct before ducking back down into tunnels under the Chiltern hills.
Known as the Northolt Tunnel, the two Tunnel Boring Machines (TBM) has now completed the first mile of the 8.4 mile twin tunnels, having both installed over 847 tunnel rings each, made up of 5,929 concrete segments.
Over 240,000 m3 of mixed soil (London Clay, chalk and sand) has been extracted during the tunnelling process so far and is being used north of the tunnel to create new wildlife habitat and landscaping. The earth is kept within the HS2 site boundaries so it doesn’t need to be removed to remote locations.
The tunnel being constructed by Sushila is the “downline” and will be where trains travelling south towards London will run once the high-speed rail line is operational. Caroline is constructing the “upline”, where trains will travel to the Midlands and North.
The first TBM was named by Dairy Meadow Primary School in Southall after Sushila Hirani, a local teacher with a passion for getting more girls and pupils from BAME backgrounds into STEM. The second TBM, Caroline, named after astronomer Caroline Herschell by Brentside Primary Academy School, was launched shortly after Sushila.
The 58,000 tunnel segments for this section of the London tunnels are being manufactured by Pacadar on the Isle of Grain in Kent. Recently the delivery of the segments has been by rail to the sidings at the West Ruislip site, reducing lorry journeys on roads.
The Skanska Costain STRABAG JV team is now preparing to begin the construction of cross passages between the two tunnels. The link between the two parallel tunnels will be used in emergencies.
The TBMs are due to reach the first ventilation and emergency access shaft at South Ruislip in Autumn 2023, after they have travelled a distance 1.7 miles. The shaft is 35 metres deep and a ‘headhouse’ will be built above it to house safety equipment. The building will have a green roof and will be constructed using timber and brick, sympathetic to the local landscape.
The 8.4-mile Northolt Tunnel will be completed with two additional TBMs which will be launched from the opposite end of the tunnel at Victoria Road Crossover Box in Ealing next winter. All four TBMs constructing the tunnel will end their journeys at Greenpark Way in Greenford in Ealing where they will be extracted from the ground.
The government’s Infrastructure and Projects Authority annual report is warning that the HS2 project is currently in a red rating, meaning that there are concerns about the delivery of the project in its current state.
The report only allocates a simple colour coding to the status, so there’s no indication as to what would get the project back on track to a green traffic light, although the constant meddling with Euston station wouldn’t have helped in this year’s report.