Bespoke solutions to rehabilitate a fragile, damaged sewer

  • Client Anglian Water
  • Date September 2019

About the project

Danaher and Walsh APS was called to a collapsed concrete pipe believed to be 150mm in diameter outside of Fairhaven Church in Freiston, Boston. However, on arrival it was quickly discovered that the pipe was 175mm in diameter and had suffered a severe hydrogen sulphide (H2S) attack.

Key aims and challenges

The excavation was quickly carried out under 3-way traffic control and a short section was replaced to restore flow. It was highlighted that the pipe was running with four rising mains entering it.

The line was surveyed via CCTV inspection. This revealed a pipe that was on the brink of collapse due to the severity of the H2S attack.

The pipe had deteriorated so severely that the joint rubbers has become displaced, creating a risk of the liner getting snagged or caught in the rubbers.

The solution was to cut out the displaced rubbers using a remotely controlled robotic cutter. However, use of a standard cutting head was deemed to carry a strong risk of causing further collapse of the decayed pipe due to the vibrations.

Danaher & Walsh APS collaborated with supplier ANT Hire to design and manufacture a bespoke diamond disc attachment, which safely cut the rubbers with no adverse effect on the pipe.

The next major challenge to overcome was the variations in pipe diameter. The main length ranged from 175mm to 210mm in certain areas of severe swelling. Due to the severity of the decay, we wanted to achieve a 4.5mm finished wall thickness on the liner to ensure structural integrity of the rehabilitated pipe.

A 150/225mm Proflex liner was selected for the task, to be cured using styrene-free, UV activated resins. This method was chosen because the liner could expand at relatively low pressure, ensuring a secure fit without over-stressing the weak host pipe, whilst still achieving the desired thickness and avoiding voids and annuluses.

The installed liner was cured using Danaher & Walsh APS’ revolutionary Sewertronics SpeedyLight+ UV LED curing system. The 67m liner was installed and then cured in just 75 minutes.

Connections were then re-opened, and the site cleared with no overtime or late night working required – minimising potential disruption to local residents.

How did we do?

Thanks to our keyhole surgery techniques, what could have been a 75-metre excavation required just two very small digs on site, massively reducing disruption, cost and carbon footprint.