Tideway TBM bores successfully under Tower Bridge

It had been feared that the tunnelling could damage the iconic Victorian structure. An Aecom report of 2013 had suggested that the tunnelling could make the two towers rotate toward each other even though the effect might not cause lasting structural damage. In the event, the invar barcodes installed by Tideway to detect any untoward movement during tunnelling did not register any troubling effects. The movements detected were said to be within tolerable levels.

Around 500m before Tower Bridge, the TBM was paused for a period of around three weeks in the vicinity of HMS Belfast. Tideway later confirmed this was for general maintenance reasons.

With an 8.8m diameter, weighing 1,300t and more than 100m long, the machine is – with sister TBM Millicent – the project’s largest TBM. Both were built by NFM in Le Creusot, France and shipped to London via Hamburg, a distance of more than 500 miles (800km).

Ursula will finish boring at the Chambers Wharf site in Bermondsey, marking 7.6km of tunnelling from her launch in Battersea. The TBM has so far installed 4,227 concrete segments. Working west to east, the machine has navigated a broad 90-degree bend which started at Victoria Embankment and finished at Blackfriars. As it continues to work from west to east, Ursula and the other five TBMs working on the project have now completed around 19km of the total 25km tunnel length.

The central section of the project, between Fulham and Bermondsey, is being jointly delivered by contractors Ferrovial and Laing O’Rourke. Two other machines have already completed the first stage of tunnelling from Battersea to Acton (western section), and the most easterly section from Bermondsey to Stratford will start soon.

Tideway runs mostly under the River Thames at depths of 30–65m, transferring sewage eastwards under gravity. The £1.1bn (US$1.4bn) project is designed to intercept, store and ultimately prevent around 39 million tonnes of raw sewage entering the river annually through combined sewage overflows. Construction is scheduled for completion in 2025.