Anglian Water team completes 'Mission Impossible' sewer repair

Danaher & Walsh's dedicated Anglian Water team recently completed a challenging sewer repair, internally dubbed Mission Impossible.

The problem

Working on the Water Recycling Network alliance contract, D&W was tasked with solving a tricky sewer collapse, partially located underneath an entertainment complex on Skegness's busy seafront.

A 300mm surface water sewer, lying 4m beneath the building, had several collapsed sections. The sewer was partially flowing, but heavy rainfall was causing flooding in low-lying areas and to the basement of the Embassy Theatre - resulting in cancelled shows.

The most obvious solution was to install a section of ductile pipe within the existing pipe, as close as possible to the existing internal diameter. This would be achieved by winching the replacement pipe in place from the downstream manhole. 

The alternative would have been to excavate and replace a section of pipe, however, this would have required a timber ‘mineshaft’ to be constructed inside the amusement arcade. The excavation would need to be hand-dug, with spoil removed via conveyor belt. This was assessed to be costly, high-risk, disruptive and subject to highly restrictive access. What's more, the arcade is full of heavy slot machines and has a solid flagstone floor. 

The affected pipe was blocked with rubble, brick, paving stones and even metal. It was clear that there was a danger of debris falling back into the pipe immediately after jetting, because the surrounding ground was unstable. 

The job would have resulted in compensation payable to local businesses, with trade disrupted and roads and pedestrian access closed for approximately four weeks. 

Debris blocking the sewer

The solution

The project team, comprising Danaher & Walsh, Anglian Water and supply chain partner Wilkinson Environmental, assembled to consider alternative solutions.

The pipe was completely full of rubble, brick, paving stones and even metal. The team started to investigate the possibility of injecting a solution into the pipe to stabilise the area in and around the pipe and to bind the debris together. This would allow either jetting or cutting of the debris out of the pipe.

This method has, to our knowledge, only been used once before, on a much smaller pipe. In order to assess the viability of this method, a test rig was constructed in a workshop environment. The test proved a success, giving the project team cautious optimism.

The repair

The resin injected into the sewer

A 200-400mm inflatable packer was sourced. The packer was positioned in the collapsed pipe and inflated using an air compressor. The packer had two small-bore plastic pipes running through the middle. These two small pipes were to allow a glue-like solution to be injected in. Valve attachments built into the steel casings at the front and rear of the packer to acted as stoppers.

The ‘glue’ was an MC-Injekt 2133 foaming chemical resin, which is a polyurethane-based product that reacts when in contact with water. MC–Injekt is commonly used to seal cracks and cavities to stop water infiltration in tunnels and deep construction.

The injection was executed using a hand-operated, one component pressure pump that forced the resin through one of the pipes. Water was then injected through the second pipe, activating the resin and making an expanding, foamy, glue-like substance. This expanded around the debris, before setting after 45 minutes. 

A robotic cutter was then sent into the pipe to cut our the resin and encapsulated debris from a manhole 43m upstream.

The inflatable packer had been wrapped in polythene material and covered in grease, meaning it could be deflated and pulled out of the pipe. 

A patch lining was then installed to repair the original pipe. This whole process was repeated several times to repair the whole section of troublesome sewer.

The verdict

Repaired section of sewer

It felt good to do something different. Now we’ve proved the process works, it could be used on other jobs. This was quite unique within Anglian Water and only tried once by another water company that we know of, so it was really innovative in that respect.

Simon Newlove, Anglian Water

Projects like this really demonstrate that if the right people can push beyond the given norm of what can be repaired conventionally, totally awesome results can be achieved. Taking on board the risk of the job, and the huge cost to dig this as any other collapse, led the team to try something that gave us an amazing result.

Keith Garfoot, Anglian Water