Following the completion of the primary lining on the super sewer, the project has hit another significant landmark with the completion of half of the secondary lining.
While the primary lining, was formed of pre-cast segments that form a ring, this concrete inner shell is poured in situ by a machine called a shutter.
In order to create another section of secondary lining, shutters are moved into position, concrete is pumped around the edge and set before the shutter is moved along
The advantages of secondary lining are the super sewer's extra strength and providing a smooth surface over which the flows from the sewer network can travel once the tunnel is operational.
According to Kirtling Street Project Manager Ignacio Tognaccini: "Reaching the halfway mark for secondary lining on the super sewer is a fantastic achievement, especially so soon after finishing the tunneling. The team has made great progress across the Tideway project, especially here on the central section between Fulham and Bermondsey, where the secondary lining is now complete."
The completion date of the tunneling process on this project was April 2022, with TBMs Selina and Annie both finishing their drives. TBM Selina was creating the final, easternmost 5.5km section of the super sewer among Chambers Wharf and Abbey Mills Pumping Station, whereas TBM Annie dug the connection tunnel with a 4.5 km length that is linking Greenwich to the main tunnel.
This segmental primary lining and the poured secondary concrete lining, gives the tunnel an internal diameter of 7.2m – which is the width of three London buses side-by-side.
There have been a total of 1,000 pours across 12.6km of tunnels from Carnwath road to Chambers Wharf.
Four shutter were used on the central section, working concurrently on the west and east tunnels
Up to 300 m3 of concrete was batched on a daily basis during the operation.
Approx. 75,000 m3 was poured in total.
Reducing the thickness of the lining reduced the concrete needed in the central section by 15,000 m3 – meaning approx. 20,000 tons of CO2 was saved.