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Project Profile N16J005

Decommissioning a Water Main Pipe with Terefil®

Pipe Decommissioning
Void Filling

The problem

The Hunter Water infrastructure upgrade project will see the region’s oldest water tunnel being replaced and re-directed underground. As part of this project an in-ground water pipe in Beresfield, NSW, was being abandoned, with a new main to be constructed by Eire Construction. The water main, built and placed in the 1920s, needed to be decommissioned. However, its location underneath a highway, school grounds and private land meant digging it out was unfeasible and filling it using traditional means would create unacceptable disruption and require access to private property.

The pipe’s construction and placement less than a metre underground meant there was a risk that it could rust and collapse, which would potentially damage the structures above it and incur high costs.

It was decided that the safest and most effective approach would be to fill the pipe.

A conventional approach would involve digging up to seven holes to access the pipe, which would take approximately a week to complete. Instead, Mainmark completed the project in just four days with a single hole, using its unique Terefil® lightweight cementitious fill.

One of the key features of Terefil® is its pumpability. Mainmark placed more than 400m3 of Terefil® along 620m of the 900mm diameter pipe in a single shift. At its peak, the Mainmark team pumped 68m3 of Terefil® per hour.

As a result, the pipe was safely filled without damage or inconvenience to the school or any local property owners.

The solution

To safely decommission the ageing water main pipe without disrupting a local school or private property owners, Mainmark used a pressure grouting technique with its proprietary Terefi l® cementitious grout. First, Mainmark had to fi ll a 620m section of the steel pipe running beneath and adjacent to several properties. Next, it had to fi ll a 115m section of the pipe running beneath the New England Highway.

It was essential that the solution be placed from a single entry point without accessing private property, that the project be completed in less than four days, and that the pipe be structurally filled for maximum safety.

The Result

The unique ability of Terefil® to be pumped across long distances made it the ideal solution for this project, particularly as there was only one access point.

Terefill® proved highly effective, with Mainmark able to pump more than 400m3 of the material over 620m, through a 900mm diameter pipe, in a single 10-hour shift.

Importantly, Mainmark’s approach meant no private property owners were inconvenienced and the pipe under their properties is now safely decommissioned.

Ben Murray, construction manager, Eire Constructions, said, “Mainmark was professional in their work and provided a safe, efficient, well-controlled work site that needed minimal supervision. Final clean-up and demobilisation was quick and clean. They did what they said they would. If Eire has to perform grouting of this nature and extent again, Mainmark would be the first to be contacted.”

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Mainmark Ground Engineering (NZ) Ltd





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