The NSP is being jointly delivered by Melbourne Water (Stage One) and Yarra Valley Water (Stage Two). The John Holland Group has been awarded the contract to construct both stages of the NSP. The NSP will help protect the Merri and Moonee Ponds Creeks from the damaging impact of sewage overflows that can occur after heavy rain as well as provide for additional capacity to the Northern suburbs.
The project involves the construction of approximately 13 kilometres of new sewer pipes ranging in diameter from 1.6 to 2.5 metres. The sewers are generally located along the Merri Creek Valley and Moonee Ponds Creek, from Reservoir to Essendon. Eight major access shafts of up to 65 metres in depth and 13 metres in diameter will also be constructed across stages one and two.
The NSP is one of a number of future projects to be delivered under a collaborative arrangement between John Holland, Melbourne Water and Yarra Valley Water. Project Managers Connell Wagner and design partners SKM-Jacobs are working with John Holland to deliver this project.
Site selection
Community Relations Manager for the NSP Trent Woodberry said that a thorough site selection and extensive consultation process was undertaken by Melbourne Water and Yarra Valley Water to determine the route of the sewer and the worksites, prior to construction. This process involved local councils, community groups, Vic Roads, Environmental Protection Agency Victoria, Local Councils, State Government departments and local Members of Parliament.
Working with the community
Mr Woodberry explained that one of the biggest challenges is running 24 hour operations in an urban environment. “Many of our project sites are located in densely populated areas, meaning that community engagement is of the utmost importance.”
Seeking to minimise the potential impacts on the community was a major factor in the planning and design of the project and continues throughout the construction phase. Community forums are held on a regular basis to provide opportunities for residents and businesses near the shaft sites to receive updates on the project, and raise any questions or areas of concern. Community members attending these sessions have provided useful feedback on ways in which the project can minimise possible impacts.
The NSP team have also involved local schools as a key partner to the project by offering them an opportunity to name the three Tunnel Boring Machines (TBMs) to be used for construction. Local Primary School students in grades 1 to 3 were invited to colour in and name the TBMs. The chosen names were TBM 1 – Victoria, TBM 2 – Gemma and TBM 3 – Julia.
Managing the environment
During the project’s planning phase a number of detailed investigations were completed including an environmental assessment, which incorporates a biodiversity study, and archaeological and heritage studies. These studies provided the basis for the development of an Environmental Management Plan which guides how construction work will be undertaken to minimise the potential for environmental impacts.
Numerous geotechnical investigation studies were undertaken prior to the commencement of tunnelling activities, in order to ascertain what sort of geotechnical conditions were likely to be encountered during underground construction. The project is tunnelling at depths of between 19 – 65 metres across both stages, through variable geology including basalt, alluvium and Silurian sedimentary formations. At various points the project will be required to tunnel through basalt up to 270 MPa and also water bearing alluvial’s.
Constructing the tunnels
Three state-of-the-art TBMs have been specially designed and commissioned for use on the NSP: two Herrenknecht Earth Pressure Balance (EPB) TBMs and one Robbins Hard Rock TBM.
These TBMs are highly advanced and designed to operate in specific geological conditions. The Herrenknecht TBMs are designed to operate in mixed ground conditions, while the Robbins TBM will be used to excavate through hard rock, such as the basalt conditions expected on Stage Two.
Stage One – Melbourne Water
John Holland began construction on Stage One of the NSP in August 2007. Stage One involves 8 kilometres of sewer tunnel connecting to the existing sewerage system near Merri Creek at Coburg and the Moonee Ponds Creek at Pascoe Vale. The crews will use the two Herrenknecht EPB TBMs to complete Stage One.
Shaft excavation is underway or has been completed at three of the five NSP Stage One sites. Tunnel construction on the 1.6 kilometre tunnel length from De Chene Reserve, to connect to the Carr Street shaft is well underway. This tunnel is being excavated using an EPB TBM “÷Victoria’, which is the first to be used on the project. “÷Victoria’ is anticipated to reach the shaft site in Carr Street towards the end of 2008.
To facilitate 24 hour tunnelling operations three sophisticated acoustic enclosures have been constructed over the three main shafts. The bored piling works at the Bass Street and Vanberg Road sites have also been completed, ahead of schedule.
Stage Two – Yarra Valley Water
Stage Two of the NSP is a 4.6 kilometre long, deep-tunnelled sewer running from Carr Street in Coburg to L.E. Cotchin Reserve in Reservoir. It will connect to the Stage One works at Carr Street and will have a finished diameter of 1.8 metres.
In September 2007, John Holland signed a contract with Robbins for a 3 metre double shield TBM, with back-up, spare parts and cutters. The Robbins TBM will be launched from a 31.5 metre deep shaft at the Newlands Road job site.
Four access shafts of up to 39 metres in depth and 10 metres in diameter will also be constructed, enabling two specially designed TBMs – Julia and Victoria – to be utilised during construction. Drill and blast techniques are being used to excavate some of the tunnels, launch chambers and shafts.
Completion of the project is timed for mid 2012.