Thames Water have used an ultra-high pressure jetting solution to remove concrete from a sewer pipe and avoid the partial demolition of three houses.
They deployed a system powering the water jet to over the speed of sound, after discovering that the foundation concrete in the pipe was too tough for conventional robotic cutting.
The only practical alternative would have been to excavate and replace the pipe, buried three metres beneath extensions built behind the row of nine terraces homes in Ilford, London.
That would have involved the extensions on three of the homes being all but demolished, then reinstated, with the occupants placed in temporary accommodation while the work was done.
Lanes Group plc carried out the UHP jetting project on behalf of Thames Water and has now used the technique to complete other challenging concrete removal projects for the water company.
Operations Manager Calvin May said: “This was one of the toughest concrete removal projects we’ve ever tackled and involved contamination of a 150mm-diameter sewer.
“We believe the concrete may have been linked to a nearby building project. Foundation concrete is particularly hard and, in this case, had time to set solid, completely filling the pipe for 11 metres.
“We didn’t make very fast headway with a robotic cutter, which works by grinding down the concrete, so we needed a different approach.
“UHP jetting turned out to be a gamechanger. It was over 20 times as fast as using robotic cutting and prevented the need for an alternative solution that would’ve been much more costly and disruptive.”
It meant the concrete could be removed in 15 shifts, equivalent to three weeks’ work.
Lanes, which is Thames Water’s wastewater network services maintenance partner, developed a business case for using UHP jetting to ensure it would work and be cost-effective.
This led to the initial hiring of a UHP jetting system to ensure the concrete removal process was effective – not least because a tanker was having to visit the site every day to remove sewage building up behind the blockage.
A Falch UHP pump combined with an IMS Robotics jetting system was used, capable of delivering a water jet at 2,500 bar (over 36,000 pounds per square inch).
Six operatives underwent Water Jetting Association hydrodemolition training and equipment supplier instruction to gain the knowledge and skills needed to operate the system.
The UHP jetting system has a jetting nozzle on the end of a hose encased in a flexible steel coil sheath. Once guided into the pipe, a packer is inflated with compressed air to hold the nozzle firmly in place inside the pipe.
A mini camera and powerful LED lights allowed the Lanes operative to then view the jetting operation, while controlling the nozzle with a joystick to direct it most effectively at the concrete.
The concrete was removed in one-metre sections, with the exposed pipe strengthened by installing a cured in place pipe (CIPP) point liner made from fiberglass matting, impregnated with resin.
Once the resin had cured, the liner created a durable new concrete-free pipe within a pipe, with a design life of at least 50 years.
