Precision was paramount in the tunnelling of Thames Tideway West C405, as the tunnel was adapted for use as a gravity sewer. VMT’s innovative solutions, which included two industry-firsts, helped to ensure the TBM reached its destination with pinpoint accuracy and to our client’s satisfaction.
London’s underground sewers, constructed by Sir Joseph Bazalgette after the Great Stink of 1858, have served the city for over 160 years. However, population growth to around 16 million has placed a strain on the systems. The Thames Tideway, known as the ‘Supersewer,’ is one of the UK’s largest utility projects and is being constructed to collect excess flows currently discharged into the River Thames and transfer them to a treatment plant. Spanning 25 km from Acton to Beckton, with a diameter of 7.2 m and depths up to 60 m, construction began in 2016, with tunnelling starting in 2018. The sewer is expected to be complete and in use by 2025.
Excavating the gravity sewer
Six Tunnel Boring Machines (TBMs) are working on the Thames Tideway project, excavating the main sewer and two smaller connecting tunnels. Operating 24/7, three of the six planned tunnelling sections have been finished, complete with secondary lining to ensure water-tightness. Herrenknecht provided one large-diameter TBM for the Thames Tideway West C405 section, covering 6,942 m from Acton to Wandsworth. This TBM, with an outside diameter of 8,100 mm, facilitates the installation of the secondary lining to achieve the operational diameter of 7.2 m, demanding precise compliance with the design tunnel axis.
Navigating the challenges
We are honoured that our systems guide the TBM through this challenging route. The project uses the following VMT products:
- TUnIS.TBMLaser
- TUnIS.moving station
- TUnIS Navigation Office
- VDMS.Process
- TUnIS.mobile app
We specified our groundbreaking TUnIS.moving station for this important project which allows the total station to travel along the gantry instead of being mounted on the tunnel wall. Using three prisms on the tunnel wall and an electronic laser target in the TBM shield for precise position determination, the moving station offers efficiency and accuracy in tunnel construction and eliminates the need for a surveyor to accompany the advance of the machine the whole time, because recurring modifications of the total station and console are unnecessary thanks to the TUnIS moving station.
The new system underwent successful initial trials on the London Tideway Tunnel alongside VMT’s primary navigation system. These trials were so effective that the tunnelling operation transitioned to the new TUnIS moving station system for a 560 m stretch, replacing the standard VMT navigation system.
“The credit for improving time efficiencies – and therefore cost savings – mostly lies with the benefits that come with this system.”
Roy Behrend,
Chief Surveyor for BAM Nuttall,
Morgan Sindall, Balfour Beatty Joint Venture
Further efficiencies and significantly enhanced safety were made possible thanks to the site engineers and surveyors being able to use the TUnIS.mobile app for remote navigation system operation outside the control cabin. This meant much of the risky work was executed on a mobile device.