By Lynda Myer
Sushila and Caroline TBMs, which are 2,000-t TBMs and were commissioned in November 2022 and both have installed the over 847 tunnel rings each, made up of 5,929 concrete segments, have completed the 1.6 km (first mile) of the twin-bored Northolt tunnel in the capital.
Being located where trains travelling south towards London will run once Britain’s new high speed rail line is operational, the tunnel being constructed by Sushila is the downline, whereas Caroline is building the upline, where trains are due to travel to the Midlands and North.
The quantity of extracted mixed soil (London Clay, chalk and sand) during the tunneling process already is more than 240,000 m3 and is being used north of the tunnel to create new wildlife habitat and landscaping. The earth is kept within the HS2 site boundaries.
While naming of the first TBM was 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, TBM Caroline, named after astronomer Caroline Herschell by Brentside Primary Academy School, was launched shortly after Sushila.
Operating of each TBM, and working closely with a 60 strong team on the ground, is up to a team of 17 tunnel engineers from HS2’s Main Works Civils Contractor, Skanska Costain STRABAG joint venture (SCS JV).
Pacadar on the Isle of Grain in Kent is producing the 58,000 tunnel segments for this section of the London tunnels and the method for delivery of the segments was by rail to the sidings at the West Ruislip site, decreasing lorry journeys on roads.
Additionally, construction of cross passages between the two tunnels is the current program of the SCS JV team, while the link between the two parallel tunnels is slated to be used in emergencies.
Following passing a distance 2,74 km (1.7 miles), TBMs are due to reach the first ventilation and emergency access shaft at South Ruislip in Autumn 2023. The shaft is 35 m 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 scheduled date for completion of 13.52 km (8.4 miles) long Northolt tunnel is 2025 and two additional TBMs are due to be used, which will be started up from the opposite end of the tunnel at Victoria Road Crossover Box, close to Old Oak Common station, 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.
