Progress made following delays due to social distancing rules
The nearly completed Frogmore Connection Tunnel. Picture: Tideway
The Frogmore Connection Tunnel, which runs from King George’s Park all the way through to Thames Tideway’s mammoth London Super Sewer project, is now complete with its all-important secondary lining.
All that’s left to do is a thorough cleaning, finish the grouting, and fixing any snagging.
The 1.1km connection tunnel was excavated using a boring machine called Charlotte, after local suffragist Charlotte Despard, which first mined south from Dormay Street to King George’s Park then - after a short journey by road back to Dormay Street - north and under the Thames to Carnwath Road in Fulham (see the diagram below).
Map showing the Frogmore Connection Tunnel. Picture: Tideway
When the UK went into lockdown in March last year, the tunnel was just a month into the secondary lining production when the construction team had to stop work immediately.
The 2.5m internal diameter of the connecting tunnel meant that social distancing was a huge challenge, which was only overcome by way of a group effort from Tideway’s main works contractors Bam Nuttall, Morgan Sindall and Balfour Beatty, along with specialist tunnelling firm Kern.
Project Director Sally Cox said: “Well done to the entire team for completing the secondary lining of the Frogmore Tunnel. It has not been an easy one with the disruption of Covid in the middle of the works, but the team have worked brilliantly in making it a success.”
The team used a system of four individual ‘shutters’ to cast the concrete in place, utilising a ‘hit and miss’ sequence which allowed for faster production.
A total of 1,420m3 of concrete was used for the secondary lining and the team was eventually able to cast an average of 60m each week – with a peak production rate of 72m.
The expansion of London’s sewer network started in 2016 and was due to finish in 2024, but has now been delayed by the pandemic to early 2025.
Locally the 1.1km Frogmore tunnel will take sewage overflows from King George’s Park into the main 25km Super Sewer at Fulham, where it will be transferred to east London for treatment, instead of polluting the Thames.
Tideway said, “It may be hard to believe, but until the tunnel is built, we’re treating the river like a toilet. Raw sewage flows directly into the Thames when it rains, as this is the only way to stop homes and streets from flooding when the existing Victorian sewers overflow.”
The Frogmore Connection Tunnel forms part of 25km of tunnels being built by Tideway under London, which will divert the tens of millions of tonnes of pollution that are currently entering the river every year to specialist treatment plants.
The Super Sewer will cost £3.8 billion, with an additional £1.1billion having already been spent by Thames Water on preparatory works. The cost of the project is being met by Thames Water’s 15 million wastewater customers.
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July 19, 2021