The Northern Sewerage Project (NSP) has involved the construction of 12.5 km of new sewer pipes ranging in diameter from 1.6 m to 2.5 m, delivered jointly by Melbourne Water (Stage 1) and Yarra Valley Water (Stage 2). The route is generally located along the Merri Creek Valley from Coburg to Reservoir; and the Moonee Ponds Creek at Pascoe Vale.
The NSP has increased the capacity of the sewerage system for Melbourne’s growing northern suburbs, while helping to protect local waterways from the damaging impacts of sewage overflows that can occur after heavy rains. It will also help to improve the health of waterways flowing into the city’s iconic Yarra River and Port Phillip Bay.
Ground conditions along the route have been quite varied, ranging from newer volcanic basalt and soft Silurian period rock, to water bearing sand. As a result constructor John Holland used an innovative combination of shaft and tunnel excavation techniques. These have included soft ground tunnelling machines, hard rock tunnelling machines, road headers, drill and blast activities and hand mining.
Reflecting on the multiple technologies used, NSP Stage 2 Project Director David Elliott said “It’s quite unusual to employ such a variety of techniques on the one project. Where possible, we also selected tunnelling and excavation methods that would best minimise any impact to local residents and businesses.”
Tunnelling success
Through innovative construction planning and design, one of the major challenges for the NSP also became its greatest success story; the simultaneous launch and concurrent operation of two tunnel boring machines (TBMs) out of a 64 m deep vertical access shaft at Brearley Reserve in Pascoe Vale South. From this shaft the 4 m diameter TBM successfully excavated through varying geology under high-risk areas including CityLink, one of Melbourne’s major freeways and a vital hub in its transport infrastructure.
Mr Elliott said it is a credit to the project partners, including designer SKM/Jacobs and project manager Aurecon, that such a large infrastructure project has been undertaken in a built up, inner-urban area with minimal community impact. He said the success of the project is thanks to the strong team behind it, highlighting the diverse skills required to deliver a project of this magnitude and complexity. The NSP team has included geologists, electricians, mechanics, tunnelling engineers, tunnellers, surveyors, programmers, community engagement and communications specialists and TBM pilots. He said community engagement has also been central to the success of the project, both in initial planning as well as throughout construction.
Mr Elliott said both Yarra Valley Water and Melbourne Water are proud to have achieved a strong safety record with minimal safety issues and incidents. “It’s also a great success, of course, that such a large project will come in under budget and ahead of time – it doesn’t happen a lot.”
Improved timelines
Despite the scale of construction, the project has been completed six months ahead of schedule and under budget. The project was originally scheduled for completion in 2012 and was completed and commissioned in November 2011. In the past 12 months, the focus of the NSP has been on safely completing all tunnel and shaft lining. Efforts are also focused on site clean-up.
Removing buildings from shaft sites in preparation for reinstatement has also commenced. Mr Elliott said the shaft sites will be restored to their original condition or better than before Yarra Valley Water and Melbourne Water commenced work.
Yarra Valley Water is also supporting the delivery of a range of projects funded through the joint NSP Community Benefits Program with Melbourne Water. These projects, which include children’s playgrounds and community recreational facilities, will provide an ongoing benefit to local communities who have been
the company’s neighbours for close to four years.
A bright trenchless future
Yarra Valley Water sees a bright future for their incorporation of Trenchless Technologies on future projects, and undertakes a lot of smaller scale trenchless work on a regular basis, using small boring equipment. This is primarily employed for work such as building and renewing water and sewerage infrastructure across their service area, which encompasses a population of around 1.7 million.
Yarra Valley Water has invested $A230 million during the 2010-11 financial year to ensure the water and sewerage network continues to meet the needs of current and future generations. This included building 89 km of sewer mains, 220 km of water mains and 22 km of water transfer mains. Trenchless Technology played a big part in this and will continue to do so.
“The NSP is just one example of our investment in our water and sewerage systems to continue to improve our service levels to customers well into the future,” said Mr Elliott. As Melbourne’s population expands, we must ensure that the water and sewerage network continues not only to keep up with the growth, but adapts to our changing environment.”
