TRANSPORT - RAIL | INTERNATIONAL


Coming in from West Ruislip and North Action, pairs


of TBMs have been closing on the retrieval shafts at Green Park Way from opposite sides. The shafts were tough to build, in difficult ground with high groundwater, and on a confined site. All four Herrenknecht shields are being received at the site A special engineering solution of a ‘steel can’ was


developed to sit in the shafts and received the TBM, without dewatering the ground outside. The TBMs maintain pressure, advance and behind them the tunnel lining is completed, up to the shaft. With boring finished and tunnel sealed, groundwater is no longer a problem, enabling the ‘can’ to be depressurized and the shield withdrawn. The first two machines to arrive, from West


Ruislip, were lifted out earlier this year. They were 9.84m-diameter ‘Sushila’ (launched October 2022, finished Dec 2024) and ‘Caroline’ (finished April 2025). The last two shields to complete are on the North


Acton drives, and are 9.11m-diameter ‘Emily’ (completed her drive in June) and ‘Anne’ (soon to finish). They were launched early last year.


Top: Celebrating completion of first of four TBM finishes on HS2’s Northolt Tunnel Above: Tunnel bored by TBM ‘Sushila’, the first finisher for Northolt Tunnel


Winter 2025 | 25


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