Tunnel boring machine (TBM) Caroline now joins Sushila on an underground drive from West Ruislip to Greenpark Way in Greenford in northwest London.
These two TBMs, which are boring twin tunnels in parallel, will take until late summer 2024 to complete their five-mile journey, travelling at an average of 14 metres per day.
TBM Sushila has already travelled more than 70 metres in the three weeks since her launch.
As she moves forwards, Caroline will install 4,207 tunnel segment rings to create the tunnel. Each ring of the tunnel is made up of seven concrete segments that have been cast in Kent the Spanish firm Pacadar.
The SCS contracting joint venture, comprising Skanska (Swedish), Costain (UK) and Strabag (Austrian), is building the most southerly section of HS2, between the Euston terminus and Northolt via Old Oak Common.
Across the entire length of HS2鈥檚 first phase, Sushila and Caroline are the fourth and fifth TBMs to launch. These TBMs are 140 metres long and weigh more than 2,000 tonnes. Each has a cutter head that is 9.84 metres in diameter, slightly smaller than the machines boring through the Chilterns鈥�.鈥�
Once Caroline and Sushila reach their destination at Greenpark Way, they will be dismantled and extracted from a 40-metre deep shaft. Separately, two other TBMs will set off towards Greenpark Way from HS2鈥檚 Victoria Road site in 2023 to build a further 3.4-mile twin-bore tunnel. Combined, this quartet of TBMs will build 8.4 miles of twin-bored tunnels between West Ruislip and the new hub station at Old Oak Common.聽聽
Another tunnel 4.5-mile twin-bore tunnel extending from Old Oak Common to Euston will complete HS2鈥檚 journey to its London terminus.
Spoil from the tunnels at West Ruislip will be used to form embankments for the new railway further north, and to remodel West Ruislip golf course, which is closed during HS2 construction.
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