Lanes sewer repair challenge is a winner

A challenging section of sewer almost jeopardised Severn Trent Water’s multi-million pound sewer renewal scheme in Nottingham, until Lanes came up with a clever — and award-winning — solution.

The project in Upper Parliament Street, which involved relining just 6-metres of sewer with a contract value of just £14,500, was voted overall winner in the UKSTT’s 2012 award in the ‘Small Scheme’ category.

No one had been prepared to tackle the crucial repair. The sewer was badly dilapidated with missing and loose bricks, including at the crown, but the real challenge was the changing shape and size of the sewer — 375mm diameter round at one end and 600>650mm egg-shaped at the other.

Ged Healy, Lanes’ project manager, takes up the story: “We had just won our first contract for STW’s main contractor, NMCNomenca, to work on a scheme elsewhere when this tricky problem came up so they asked us to have a look — a ‘baptism of fire’, I think!

“We were confident that we could find a solution because we have relined plenty of unconventional pipes before, so we put our heads together and came up with a plan. Like all the best ideas, it turned out to be simple, yet effective.”

Firstly the team installed a series of one-metre patch liners using an inflatable packer to line the widest 4-metre section of the sewer. But, where the 600>650mm diameter changed to 375mm, it wasn’t a gradual transition: the change from one to the other was immediate, literally a brick wall with the smaller diameter sewer built in to it. And, because of the way a packer holds its liner (i.e. not right to end of the unit) that left a 500mm section of sewer brickwork exposed.

This is where the team’s creativity came in. A 600mm section of 450mm diameter, twin wall, plastic pipe was fitted flush up to the brick face of the existing 375mm pipe and secured in place with a 375>450 tapered patch wrapped around the packer and then inflated to the 450mm diameter pipe. This created a structurally sealed extension to the 375mm pipe that overlapped 100mm into the patched section of the brick egg sewer.

Due to the thickness of the twin wall plastic pipe, this now left a 50mm void between the twin wall and newly-lined brick egg. Injecting this with expanding foam filled the void, supported the extended pipe and pushed against the brickwork, securing loose bricks and providing structural integrity. Excess foam was cut back and the face of it sealed with render. (see photo).

Ged adds: “Everything came together perfectly, and both NMCNomenca and STW were delighted by the results of the post-reline survey. On top of that, despite difficult and tight conditions and working at night to avoid affecting businesses in the area, we completed everything on time. We passed our ‘trial’ with flying colours!

Chris Jones, contracts manager at NMCNomenca, says: “Operating as one team with one common goal, Severn Trent Water, NMCNomenca and Lanes for Drains worked closely to drive efficiency through innovation to ensure the timely completion of the scheme which benefited both local businesses and customers.”