CCTV inspections of the Carlton Main Sewer – a single arch brick sewer built in 1900 – revealed deterioration and signs that it was close to the end of its operational life. An important part of Melbourne Water’s sewer network, the sewer line services a number of properties in the inner northern suburbs of Melbourne and needed to be upgraded to ensure the local community continued to receive reliable waste disposal.
Its location in an area of Melbourne which has experienced considerable population growth over the past decades also meant the sewer was reaching its capacity during wet weather events, with an increased risk of unacceptable overflows.
To address the aforementioned issues, in October 2014 Melbourne Water started work on the Carlton Main Sewer Upgrade Project, which involved 1.47 km of relining and microtunnelling to construct a new 510 m gravity sewer. Other works included rehabilitation to existing manholes, the construction of two shafts to facilitate boring and the five new manholes constructed at depths of 8-25 m.
A key requirement of the project was that the existing sewer remained operational throughout.
The relining works used a combination of spiral wound methods and cured-in-place pipe (CIPP). For the spiral wound works, the contractor selected Expanda, which lines the inside of the line with PVC. CIPP was used for the ovoid sections of pipe.
The new 1.4 m diameter sewer was constructed under Pigdon and Scotchmer St, Fitzroy, using a Herrenknecht AVN1200TB Slurry Pipe Jack tunnel boring machine (TBM). This minimised the impact on traffic and the local community.
The replacement sewer was designed to divert wet weather flows from the Carlton Main Sewer into the Merri Creek Intercepting Sewer and cater for future population growth in the area. The project formed a key part of Melbourne Water’s planning for project demand on the sewer in the future, extending the life of the existing sewer by a minimum of 50 years.
The densely populated area around the sewer was a determining factor in Melbourne Water’s decision to use trenchless technologies to complete the project. The Carlton Main Sewer runs through densely populated suburbs in inner city Melbourne, with high volumes of traffic during peak hours.
Trenchless methods allowed the utility to minimise the impact on traffic, parking and public transport. It also meant it did not have to dig up the existing road and replace the existing line, which would have been a challenge due to its location 6-12 m underground.
Trenchless also allowed the existing sewer to remain operational throughout project works, meeting one of the key requirements of the project brief.
While the spiral wound method can be performed while sewer flows are still running through the pipe, for the CIPP works a bypass pumping system was set-up for short periods to divert flows aboveground.
Melbourne Water’s Andrew Moorhouse, who was Senior Project Manager on the Carlton Main Sewer Upgrade, says that non-invasive methods are perfect for Melbourne’s highly populated inner-city environments. He says the John Holland–KBR JV which completed the works on behalf of Melbourne Water, faced further challenges controlling noise and vibrations from the construction.
“Trenchless technology is a great way for us to undertake essential upgrade works in some of Melbourne’s most built-up areas,” Mr Moorhouse says.
“We’re responsible for managing a network of over 400 km of sewers and much of this network runs through densely populated suburbs. Using trenchless technology means we can get the job done fast, and also with minimal impact on the community.”
“Initially, the design involved constructing a new small diameter sewer that would have required the construction of five shafts in the roadway to support tunnelling works. Our contractor John Holland-KBR JV ended up amending the design to increase the diameter of the new 510 m sewer, which meant only an entry and exit shaft was required to support tunnelling activities.
“We were really pleased with this result as it significantly minimised impacts on the local road and transport networks in Carlton and Fitzroy North,” he said.
After two years of construction, Melbourne Water and the JV celebrated delivery of the project in October 2016. However, with many parts of Melbourne’s water and wastewater network of a similar age to the original Carlton Main Sewer, Mr Moorhouse suggests the amount of rehabilitation and replacement work in the city will only increase in the future.
Melbourne Water recently commenced work on the Williamstown Main Sewer Rehabilitation Project, which involves using slip lining to rehabilitate the existing 4.4 km Williamstown Main Sewer. The utility also has a further two projects underway where it will be utilising trenchless methods to upgrade existing sewers in Melbourne’s inner northern suburbs – the Merri Creek Intercepting Sewer Rehabilitation Project and the Merri Creek Main Sewer Rehabilitation Project. Both projects are scheduled for completion in 2017.
For more information visit the Melbourne Water website.
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.
If you have a project you would like covered in Trenchless Australasia contact Assistant Editor Nick Lovering at nlovering@gs-press.com.au