Sealing off 36″ diameter abandoned mains under King’s Road, Chelsea

November 15, 2016

As part of National Grid’s major gas mains replacement project on Stanley Bridge, King’s Road, London, a Steve Vick International Contract Service team was recently appointed to seal off the ends of three 36” abandoned cast iron mains and one 36” steel main. The filling process took just four hours to complete.

The voids needed to be sealed off to prevent backfill entering the open ends of the pipes and causing the road surface to slump over time. National Grid decided to use Steve Vick’s

FOAMBAG™ system as it offered considerable cost-saving compared with the installation and testing of traditional caps.

In each of three sections of horizontal main, Steve Vick International fitted a FOAMBAG™, the patented flowstopping system developed by the company over 30 years ago which has become a gas industry standard method. Expanding expanding polyurethane resin foam is injected into the fabric bag and is held in place as it expands.

At full expansion, some of the foam seeps through the semi-porous material to adhere to the pipe wall.

Once cured, a lightweight fabric FOAMCAP™ was fitted to the end of the main; again foam was injected to fill the space between the bag and the cap.

The fourth main was a 2 metre vertical section, 2.5 metres underground. As this was a particular hazard to workers, pedestrians and animals that could fall into the deep opening, it was completely filled with expanding resin foam. A sponge ‘dam’ was installed at the base of the vertical section and the main was filled progressively, allowing each fill to cure before adding the next.

Authorising Engineer Michael Lench said “The Steve Vick Contract Team were helpful and ensured the job went smoothly. All four mains were sealed to the high standard National Grid expect”.

As well as being used to fill abandoned pipes and many other types of void, the FOAMBAG™ technique is used for flowstopping live gas mains to be abandoned.

The bag is installed in the main, and the resin injected, via a specially constructed standpipe. The benefits of using FOAMBAG™ over conventional flowstopping methods its low cost and ease of use and the need for a considerably smaller excavation.