Thames Water is upgrading a brick-built Victorian sewer above Baker Street tube station with no traffic disruption.
Thames Water has installed a stainless steel bridge and liner constructed off site, dismantled and rebuilt inside the sewer.
The Kings Scholar Pond sewer, 2.1m under the junction of Baker Street and Marylebone Road, and on top of the London Underground’s Hammersmith and City Line, was found to be in need of repair during a routine inspection.
The structure was lowered underground one piece at a time through a narrow manhole and has had no impact on the roads above or rails below, with the 1850s-built tunnel also remaining in full wastewater operation throughout.
During the repair, all that can be seen from above ground is three small fenced off areas of pavement to allow safe access through the manhole and store equipment.
Underground, in addition to the steel structure, the team has inserted a reinforced resin liner to strengthen the sewer for around 120 years.
The steel structure has been designed to not require maintenance for the duration while the liner can be removed a panel at a time to allow the original brickwork to be inspected as normal.
Watch a video of the work here.
Thames Water project manager Asad Hanfi said: “This is one our most challenging sewer repairs ever. We’re taking the pieces of a giant 3D jigsaw underground through a hole no wider than the wheel of a van, and piecing it all together to reinforce the existing brickwork and improve the resilience of the sewer for more than another century.
“By doing it this way we’re not impacting on the busy roads or trains, and we’re saving money and significantly reducing pollution by not using large mechanical diggers. It’s better for the environment, better for our customers and it’s keeping London moving.”
During the project, which is due to run into early 2019, wastewater flows are being carefully managed, with a system of cameras and alarms used to alert teams to evacuate if necessary, as the sewer is used to carry overflows from neighbouring tunnels during periods of heavy rain.