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Super sewer drives its way through London passing underneath 21 bridges

Super sewer drives its way through London passing underneath 21 bridges

Tower Bridge, visible from the sky, with Chambers Wharf,
the tunnelling machine's finish line, visible toward the left of the image.

A giant tunnel as wide as three double decker buses has this week been dug under the final bridge in London before completion.

Passing underneath Tower Bridge on Monday marked the last passage under the 21st bridge over the Thames as it works from west to east, with 19km of tunnel now constructed.

The 25km ‘super sewer’, which will clean up the tens of millions of tonnes of sewage that currently pollute the River Thames, has had its outer tunnel shell built underneath west and central London and will soon start its final phase of digging in the east.

Tideway, the company constructing the tunnel, has been using huge tunnel boring machines (TBMs) since 2018, with a number of sections of the tunnel already having their first stage complete. Once the outer shell is in place, the team then line its concrete segments with an inner layer of concrete , in a process called ‘secondary lining’.

Roger Bailey, Tideway’s Chief Technical Officer, said: “Getting these giant machines to work away under the river has taken a huge amount of engineering expertise and successfully passing under the last bridge in central London marks an important milestone for the project.

“Most people have no idea that this massive tunnel is being built right in the centre of London, underneath one of the world’s most iconic cities, and the last bridge to pass under is perhaps the most famous.

“Our engineering and construction teams, working closely with the bridge’s owner, the City of London Corporation, have done a superb job – and we’re now closer than ever to a cleaner River Thames.

In a nod to the tradition in the tunnelling world, Tideway has named all of its machines after empowering women from London’s history and it was Ursula, named after the British cryobiologist Dr Audrey ‘Ursula’ Smith, which passed under Tower Bridge this week.

Details of the other five TBMs being used to create the super sewer and clean up the River Thames are available here

A tunnel segment being manoeuvred into place

Ursula will finish her journey at the Chambers Wharf site in Bermondsey, marking 7.6km of tunnelling from where she picked up the job in Battersea, using 4,227 concrete segments to form the tunnel. Two other machines have already completed the first stage of tunnelling from Battersea to Acton, and the most easterly section from Bermondsey to Stratford will start soon.

The central section of the project, between Fulham and Bermondsey, is being jointly delivered by contractors Ferrovial and Laing O’Rourke.  

The project is due for completion in 2025 and so far, has created more than 4,000 jobs from across its 24 construction sites. For more information and to view a live TBM Tracker, visit

Video footage of the project is available on request.

TBM Ursula before launch in May 2018