Work has been completed to protect a huge Edwardian sewer from the effects of upgrade work by London Underground beneath the City of London.
Engineers from Thames Water’s developer services worked around the clock at the Bank-Monument station complex as part of a major project to increase the station’s capacity and build a new tunnel.
The team divided the eight-foot-wide cast iron sewer, which was built in 1905, into 10 parts and reconnected them with flexible joints, allowing the 80-metre long sewer to flex and accommodate ground movement during the London Underground work.
Project manager Andy Jankiewicz said: “The planning and design for this stage of the overall works took over a year, but once we started on site the work took two months.
“It’s a combined sewer, so we diverted the foul waste into another sewer, but we had to stop whenever it rained. We worked in shifts 24 hours a day. It was very satisfying to complete the work, especially without a single health and safety issue.”
The sewer transports waste from thousands of homes and businesses in west London on its journey to Beckton sewage works.
(Project manager Andy Jankiewicz in the sewer)
Without the flexible joints, the tunnelling work under the sewer could create a void, and without protection work a section of the pipe could sink into it, due to the pressure of the soil above.
Large band seals were installed on each joint, to prevent sewage from escaping and groundwater from entering.
The seals will be monitored remotely over the next three years to see how much they stretch, then removed once there’s no further ground movement.
Project engineer Jane Battle said: “The sewer was too big to move, and building a new one would have been a massive endeavour. We also couldn’t insert a concrete lining because that would have significantly reduced the sewer’s capacity. So the only way to accommodate London Underground’s tunnelling was to create these joints.
“We initially planned to remove almost 400 nuts and bolts to create the joints, but it turned out we could undo most of them with spanners, which shows how well they’d been protected by the original concrete lining.
“When we return in a few years’ time, we’ll be able to put the nuts back on and make good the concrete lining.”
The work of developer services – part of the Infrastructure Alliance – often involves enabling large housing developments, but the team also protect the company’s assets when other organisations are working near them.
Developers spend around £20m a year diverting mains and sewers in the Thames Water region.