In late November, a giant tunnel boring machine (TBM) finished its 7.6km journey from Battersea to Bermondsey after breaking into a deep shaft at Tideway's Chambers Wharf site.
TBMs working on Tideway have now successfully passed beneath 21 Thames crossings, including Tower, Waterloo and Westminster bridges.
Mark Sneesby, Tideway's COO, said: "This is an important day for everyone on the Tideway project, as well as for and the River Thames.
"With around four-fifths of the tunnelling now complete, everyone on Tideway is focussed on getting this job done safely and delivering a cleaner Thames for the city."
TBM Ursula's breakthrough now means that more than 19km of the Thames Tideway Tunnel (as the super sewer is formally known) has been completed, with work on the remaining 5.5km section due to begin very soon.
Viv Jones, project director for the central section, said: "The hard work from our teams on-site and below ground has enabled us to safely continue tunnelling despite COVID - and continue work on this vital piece of infrastructure.
"Ferrovial and Laing O'Rourke, the contractors on the central section, have done a fantastic job, and I thank the teams involved for their efforts to clean up London's iconic river."
As part of its drive, TBM Ursula excavated over a million tonnes of spoil, all of which was removed from site using barges on the Thames - preventing more than 250,000 HGV trips.
Around 240 barges were also used to transport concrete segments to site. These segments slot together underground to form the rings which make up the tunnel. This section of the tunnel is formed of 4,227 rings.
Tim Newman, Tideway's project geologist, added: "Completing the longest single drive on the Tideway project is a wonderful milestone, and our teams have made great progress through a challenging year.
"TBM Ursula has tunnelled at incredible depths, encountering a real mix of geology - through clay, sand, gravel and chalk. The expertise required for such a task is immense and allowed us to quickly and safely adapt the tools on the cutterhead as needed."
TBM Ursula will remain in place at the bottom of the shaft while the team at Chambers Wharf prepares to launch TBM Selina, which will create the final and easternmost section of the super sewer.
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