Bawdsey land drainage pumping station and its 450 mm diameter discharge pipeline were built in the late 1950s to serve an agricultural catchment of nearly 13 square kilometres, half of which lies at or below mean sea level. The Bawdsey Pumping Station automatically controls water levels and discharges surface water drainage through the pipeline, under a flood defence embankment and into the tidal estuary of the River Deben. The overall pipe is about 30 metres long. However, a 22 metre long section, from the pumping station to the outfall, has deformed under the weight of the embankment and sunk about 250 mm into a shallow ‘U’ shape. When the pump operates at its flow of 0.45 metres cubed per second and pressure head of five metres, water is forced out of the damaged pipe’s open joints, jeopardising the integrity of the flood defences.

A swallow hole appeared in the embankment, forcing the Environment Agency, which is responsible for the embankment, and the East Suffolk Internal Drainage Board (ESIDB), responsible for Bawdsey Pumping Station, to act quickly. The ESIDB is one of a consortium of five boards making up the Water Management Alliance (WMA), which together protect about 1,220 square kilometres of East Anglia. There was an acute risk of an embankment breach and the WMA looked at alternative repair options.

“We had to act quickly and considered various alternatives, including replacing the entire section of pipe, but that would have required major invasive surgery to the embankment,” says WMA district engineer Ian Hart.

“Instead we opted for a less invasive option of relining the pipe without the need for any excavation, in the spirit of modern, keyhole surgery.

I contacted Aarsleff and they confirmed the feasibility of repairing the pipeline in-situ with a tailor made liner. We then appointed a local civil engineering contractor, Breheny, to oversee the repair as they had rebuilt the pumping station in 2003–04. Aarsleff purpose-made the liner to suit and installed it in a very slick and professional operation.”

Breheny provided clear unobstructed access to the pump house, removed the pipeline inspection cover within the pumping station and opened the outfall flap valve to allow Aarsleff to make a start on the lining during low tide. A thin plastic pre-liner, with a blanked end, was first inserted into the damaged pipeline using compressed air to protect the main resin-impregnated polyester liner during installation. The main liner was designed and made by Aarsleff’s in-house designers to withstand the positive and negative pressures and the high flow rates generated when the pump operates. It was made inside out from resin impregnated thin layers of special needle felt so that the outside surface eventually became the inner smooth bore surface when the liner was inverted into the damaged pipeline. The main liner was packed in flake ice during delivery from the factory to the site to prevent premature curing.

At the pump house the liner was wound into the special inversion drum, which was positioned close to the pump house entrance. A length of liner, twice the distance from the drum to the pipeline manhole, was pulled out of the drum. This protruding section was then turned back on itself so the inside of the liner was now on the outside. It was pushed onto the outlet nozzle of the inversion drum and held in place with special clamping bands. The liner was then lowered down into the manhole and guided by hand a short distance into the pre-liner and into the entrance of the damaged 22 metre long pipeline. The inversion drum was then pressurised with compressed air, which forced the liner, with its closed end, to rapidly unwind from the drum and unfold and invert itself through and out of the open end of the damaged pipeline. The inversion process only took a few seconds with the air pressure forcing the liner through the prelined damaged pipe and against the wall, which effectively acted as a former for the new lining.

A steam pressure hose was then connected from a special boiler to the inversion drum to heat up the liner. At the same time a steam exhaust pipe was also inserted into the exposed section of liner protruding from the outfall. Temperature probes were attached to the liner, which was gradually heated by the steam to 110°C and held for four hours to cure the resin-impregnated, 13 mm thick liner. By using steam curing, the required high temperature could be maintained, even though the end of the liner was submerged during high tide. The entire liner inversion and curing process was controlled and monitored by a computer on board a self-contained lorry fitted with highly advanced, purpose-built installation equipment, including the boiler and compressors, needed to perform the No-Dig, CIPP process.

After curing and cooling, the ends of the new liner, which formed a self-supporting pipe within a pipe, were cut off at the next low tide. Aarsleff’s lining crew completed their work in just one and half days and Breheny followed on, restoring the outfall flap valve and returning the pump house to full working order. The repair to the Bawdsey pipeline was completed without any excavation or disturbance of the pipeline and was done in a fraction of the time and at a fraction of the cost it would have taken using conventional, open-cut pipe replacement methods.