Yarra Valley Water recently rehabilitated more than 50 km of its infrastructure using trenchless relining.
The Hawthorn sewer network collects flow from local residential properties and transports it to sewage plants for treatment and disposal. Some of the pipes in this network have been providing this service for more than 100 years and are in need of renewal.
After conducting inspection and condition assessment, utility Yarra Valley Water – which provides water supply and sewage services to more than 1.9 million people and 50,000 businesses in Melbourne – identified in excess of 50 km of pipeline that was old, in poor condition or had experienced multiple blockages within the past few years.
To improve and extend the assets’ service life, as well as to mitigate sewage spills to the environment during heavy storms, the organisation engaged two expert trenchless relining contractors to rehabilitate the sewers.
Preparing for improvement
The tender phase for the rehabilitation project began in mid-2017, with contracts awarded soon after.
Before any rehabilitation took place, CCTV equipment was placed in the sewers to complete a comprehensive inspection of the assets. The footage was used to determine the condition of the inside of the sewers based on a visual inspection.
This data subsequently informed the suitability for relining in the assessed section and used to provide information about the condition of property junctions and the associated recommended treatment. In some cases, where an entry point was not immediately visible, excavation down the pipe or buried manhole was carried out.
Trenchless relining on the Hawthorn-based assets then commenced in December 2017. The diameter of pipes that needed rehabilitation varied between DN 100 and DN 300, with sections of pipeline rehabilitation ranging from lengths as short as 1 m, which were generally adjacent to longer sections of relining, to longer sections that were more than 100 m in length.
A majority of pipes rehabilitated as part of this project were made of concrete, though there were also some terracotta pipes encountered. At the time of publication the project was ongoing, but in the final closeout stages addressing lines that were not accessible previously.
In order to choose the right contractors for the project, a five-person panel was selected to assess the tenders submitted. The panel was selected from a variety of Yarra Valley Water divisions, including Programs and Renewals; Safety, Health, Environment and Quality; Asset Optimisation and Asset Planning.
The panel assessed the tender submissions on weighted criteria, including price, capability and experience, methodology and program. Contractors Interflow and Abergeldie Complex Infrastructure were selected after their submissions indicated they had the ability to meet the criteria at a competitive cost; additionally, both contractors had demonstrated their capabilities on previous Yarra Valley Water projects.
Engaged and managing challenges
One aspect of the project that Yarra Valley Water kept in mind was making sure that it stayed engaged with the community in the areas affected by relining works. In the case that works would interrupt or inconvenience residents – particularly use of access laneways adjacent to properties – contractors were required to provide seven days’ notice.
In cases where sewer infrastructure was located on private property, sometimes in backyards and below structures, there were challenges in finding an appropriate time to access the property and remove obstructions to complete works. In these instances, Yarra Valley Water’s case management team were able to provide assistance to find mutually agreeable solutions, keeping residents informed about the locations of buried infrastructure and educating them about access requirement rights.
Taking on trenchless
Yarra Valley Water has previously used trenchless technology to complete sewer rehabilitation projects in other locations around Melbourne. Trenchless solutions are on the utility’s radar for consideration when approaching similar projects.
In this case, the relining method was chosen for its ability to be carried out using existing manholes. While some cases required a degree of excavation to expose a buried manhole or access point, in general very minimal disruption to the existing ground was required.
Using trenchless relining rather than commissioning full open trench replacement significantly reduced the disruption to residents, damage to picturesque local streetscapes and reinstatement costs associated with open cut construction.
In addition, the lining – which has the potential to extend the sewers’ operational life by 50 years or more – was installed in existing pipes and has its own structural integrity, meaning it does not rely on support from the deteriorated host pipe.
Yarra Valley Water says that a combination of traditional and trenchless methods will continue to be used for future sewer rehabilitation projects around Melbourne, including relining and pipe bursting. When
it comes to deteriorating water mains, each case will be assessed, carefully considered and the most viable method of repair or replacement selected.
This article was featured in the Summer edition of Trenchless International. To view the magazine on your PC, Mac, tablet, or mobile device, click here.
For more information visit the Yarra Valley Water website.
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