Tideway project gathers pace with sprayed concrete lining completion of Chelsea Embankment Foreshore Connection Culvert

01.07.2021

Major milestone reached for London’s super sewer megaproject, with sprayed concrete lining completion of the Chelsea Embankment’s 172-metre connection culvert.

COWI, a leading international engineering consulting group, has completed the sprayed concrete lining (SCL) for the connection culvert at the Chelsea Embankment Foreshore (CHEEF) site – a vital segment of the Tideway project. This marks a significant step towards the ambition for a new major London sewer system that will tackle overflow issues from Victorian-era sewers, helping to protect the River Thames from pollution.

At 172 metres long, the Chelsea connection culvert is the longest and largest of the connection culverts on the central section of the Tideway project, playing a key role in the clean-up of one of the most polluting overflows in the system. Connecting the north and south sides of the CHEEF site, the culvert will receive sewage overflows from the Low Level 1 sewer on the north site and carry them to the interception chamber towards the newly constructed shaft on the south site that can transport them to the depth of the new super sewer.

Presenting several engineering challenges for the teams involved, the culvert has a clay cover of around 2.5 metres at its minimum, less than half the tunnel diameter. To maintain a stable excavation and minimise ground movement, the tunnel profile had to be constructed in carefully planned stages via 186 spray concrete lined advances.

A top-heading and bench sequence was adopted for the first 21 metres of the tunnel drive where the tunnel profile is at its largest. This section of the tunnel features a vertical connection at crown level where sewage flows are deaerated, allowing excess air to escape before passing back below the Chelsea Embankment road to the Low Level 1 sewer.

Chris Phillips, Project Director at COWI said: “While engineering feats of our past should be commended for their ingenuity, the world is changing, and we must change with it to ensure a positive impact on our communities and our environment. Though the 150-year-old London sewer system is still in remarkably good condition, it cannot cope with modern demands, with millions of tonnes of raw, untreated sewage spilling into the River Thames each year causing damage to sensitive ecosystems. We are incredibly proud to be part of the collaborative team working to combat this and create a safer, healthier and more sustainable city. This latest milestone at the Chelsea Embankment site is the last of the 10 SCL tunnels, totalling almost a kilometre in length, that COWI has designed as part of this project – a fantastic achievement to date and we look forward to continuing our support for the project.”

COWI has completed this work in partnership with infrastructure consulting firm AECOM, for the central section contractor (a joint venture of Ferrovial Construction and Laing O’Rourke). It is the latest progression marker in a series of key developments at the CHEEF site. Niall Watson, Project Engineer at CHEEF, commented: “With the completion of the culvert, the north and south sites of Chelsea are now connected and the civils progress is going along at full speed. Over the next couple of months, sections of the site will be handed over to the MEICA and Architecture and Landscape teams to start turning the completed civil structure into the finished Tideway product”

Completion of the Tideway project is planned for 2025.