Innovative approach to water infrastructure a win-win for consumers and utilities

Posted 6 March 2017

Prefabricated GRP maintenance hole riserAn Australian-first use of glass-reinforced plastic (GRP) maintenance holes and jacking pipes has helped deliver a major water infrastructure project six months ahead of schedule.

The Amaroo Main Sewer Project involved the installation of Australia's longest and largest-diameter sections of filament-wound GRP jacking pipes, as well as the largest-diameter and deepest GRP maintenance holes.

Yarra Valley Water and construction contractor John Holland estimate they were able to install GRP maintenance holes four times quicker than if they'd used reinforced concrete.

“It took about a quarter of the time to install and complete one of our GRP maintenance holes at just two and a half weeks,” said Yarra Valley Water Project Manager Robert Fittock.

“The vortex maintenance holes – at 5m in diameter and up to 22m deep – are complex structures with a number of internal GRP structures, which were pre-fabricated as a single unit. That meant we were able to lower maintenance holes into the shaft in two sections rather than constructing over 10 to 14 concrete lifts. 

“These structures are now able to be completed in as few as four concrete pours, with a robust and corrosion-resistant GRP internal finish.”

Although GRP maintenance holes have been installed in Australia before, the Amaroo water infrastructure project is unique because they were much bigger, deeper and did not rely on external reinforcement. 

“Traditional concrete and GRP maintenance holes require a significant amount of steel reinforcing around the base of the structure, whereas we have a non-reinforced solution,” Fittock said.

John Holland Senior Project Engineer Cameron Woodgate added that there were significant safety benefits too.

“The GRP maintenance hole solution also had the advantage of improved safety by reducing time in the shaft by removing steel-fixing, removing a number of activities requiring working at heights and reducing the number of crane lifts,” he said. 

Along with the 18 GRP maintenance holes, the project installed 8.3km of GRP jacking pipe (mostly 1.6m in diameter) and numerous sensitive crossings: two creek crossings, two Hume Freeway crossings, three VicRoads Crossings and four Melbourne-Sydney rail crossings. 

“This is the longest GRP drive completed in Australia. We've pipe jacked an 800m-long curved drive, which is record breaking for this pipe material,” said Woodgate.

“The reduction in the maintenance hole construction times as well as the improved tunnelling production were the main reasons for bringing the project in six months ahead of schedule.”

The GRP was Australian manufactured, with RPC Technologies providing the maintenance hole solution and RPC Pipe Systems producing the piping. Fittock said YVW and John Holland chose the filament-wound GRP pipe after being convinced it provided the best value for money and fit-for-purpose solution. 

“To demonstrate the performance of the pipes prior to installation, and provide more confidence, [RPC Pipe Systems] built a bespoke compression rig to test those pipes to the full jacking forces they'd experience in addition to a full suite of testing,” he said. 

The $130 million Amaroo Main Sewer Project will service a projected 300,000 additional people living in Melbourne's northern growth corridor by 2050, and is scheduled for practical completion in April this year.