The rehabilitation required a unique solution to navigate difficult bends, high operating pressures and took place in a location that prohibited traditional rehabilitative methods.
Sydney Water has a long-term contract to supply a large volume of recycled water to the largest steel fabricator in Australia via a mild steel DN 500 main. In December 2016, this high-pressure main experienced a catastrophic failure following undermining of thrust blocks, inclination of thrust blocks and disjoining of sleeve sockets of the pipe at a major rail crossing.
The main was immediately shut down so that the investigation and selection of suitable repair method could be made, while Sydney Water maintained supply to the steelworks using potable water.
Swift solution
The utility needed a robust and swift solution and conventional dig and repair methods were not possible because the failed section was below a railway. Horizontal directional drilling was ruled out because one end of the main was located near a creek, bridge and many other services.
Designing and constructing a pipe bridge would have been a very costly option and would have taken too long to execute. Traditional rehabilitation methods, including sliplining, were also ruled out due to the main’s environment, including an operating pressure of 14 bar, a number of 45° angle bends and one 90° bend.
Sydney Water decided to repair the main using the Kevlar reinforced Primus Liner, following on from a history of other successful rehabilitation projects that included difficult bends and high pressure.
On investigation, Primus Line engineers determined that the sweep in the 90° bend was too tight and the pressure was too high for the medium pressure Primus Line DN 500. Instead, a high pressure DN 400 Primus Liner with an operating pressure of 20 bar and a burst pressure of 100 bar was chosen.
The host main was carefully inspected and prepared so that it would not damage the liner during the installation process or during operation. A portion of this high-pressure main is above ground and a failure in 2016 had caused the foundation of a thrust block for the change of direction, running from the above ground section to the buried railway crossing section, to be undermined.
External consulting engineers recommended the construction of a new thrust block with deep pilings, but this was not possible due to its close proximity to the railway track and nearby services. Sydney Water engineers developed an innovative solution that involved continuously extending the liner to the location of the next existing thrust block.
This design measure was expected to allow any thrust at the undermined section to be transferred and restrained by the combination of the weight of the water filled Primus Line and the next thrust block.
True value propositions
In 2017, Primus Line trainers travelled to Australia from Germany to train Sydney Water in the Primus Line installation process. What made this project unique was that it was installed and self-performed by the utility.
One of Primus Line’s true value propositions is that after training there is no investment required to install Primus Line, as it’s pulled into place with an approved winch and inflated into shape using an oil-free air compressor.
In this case Primus Line was the obvious choice as it met all of the project criteria – it was able to navigate the bends, including one at 90°, and maintain the 14 bar operating pressure. Furthermore, the low-cost installation process was able completed quickly with no curing, taking only 20 minutes.
This article was featured in the March edition of Trenchless Australasia. To view the magazine on your PC, Mac, tablet, or mobile device, click here.
For more information visit the Primus Line website.
If you have a project you would like featured in Trenchless Australasia contact Journalist Chloe Jenkins at cjenkins@gs-press.com.au