Difference the project will make
The Tideway Tunnel – nicknamed the super sewer – aims to make the river Thames cleaner for both Londoners and river wildlife.
Currently, even a moderate amount of rainfall can mean sewage and other social excreta overflows into the Thames and floats past the House of Commons.
High levels of sewage also affects wildlife. When a large amount overflows into the river, the bacteria that breaks it down sucks oxygen out of the water – suffocating and killing fish.
When the tunnel is finished, the system should only overflow in severe weather conditions such as 3 days of solid rain.
How the work is being done
The Thames Tideway Tunnel will be 25km long, 66m deep and 7m in diameter.
It will follow the route of the river Thames and go through ground conditions including chalk and clay.
Engineers will use 3 main ‘drive sites’. This is where the tunnel boring machines (TBMs) will be lowered into the ground via vertical shafts. They’ll dig the tunnel in 3 sections – east, central and west.
Each TBM uses a rotating cutterhead to dig. At the same time, the machine creates a tunnel wall behind it using concrete segments. Waste material is removed using a conveyor belt or pump, depending on the ground. In some areas the waste is solid, in others it will be more liquid – known as slurry.
The TBMs will be transported along the river by barge to where they’re needed. The first TBM arrived in November 2017.
Tunneling starts in 2018 it will go on for 24 hours a day.