The MMSR is a major urban infrastructure project that will replace a section of Melbourne’s main sewer that has been servicing the city and inner southern suburbs for over 100 years.
The MMSR will be using a LOVAT tunnel boring machine (TBM) to excavate the pipeline, ensuring that much of the necessary activity can take place underground.
The estimated total coat of the project will be $220 million, which will be funded by the Victorian State Government.
MMSR project scope
The original Melbourne main sewer was built between 1894 and 1897. Melbourne Water said that the old sewer requires replacing, due to its age and capacity, to keep up with urban growth. The capacity of the new sewer will be four times greater then the existing sewer.
Construction work for the MMSR will include the replacement of approximately 2.214 km of the existing Melbourne main sewer from the Docklands in the north to connect with the Hobsons Bay main sewer in Port Melbourne. The diameter of the replacement sewer tunnel will be between 1.5 – 1.8 m at a depth of between 10 – 15 m.
The MMSR will also involve the removal of the North Wharf pump station and a staged sheet piling process for the Yarra River.
TBM
The TBM will be a specially designed earth pressure balance machine of 2.952 metres in diameter to construct a 2.4 metre ID segmental tunnel lining. The TBM will have an 11 metre shield length and measure 92 metres in total length, including backup. The TBM is being designed to be capable of cutting a maximum of 150 mm per minute.
Six vertical access shafts 10 – 15 m deep will be excavated along the sewer corridor providing access for the TBM to be inserted and retrieved. These shafts will then act as future manholes.
The TBM will bore into the ground at the key construction site of Fennel Reserve in Port Melbourne. It will first head south to the Swallow Street shaft where it will be removed and then re-inserted at Fennell Reserve shaft to then tunnel north to the South Wharf shaft on the bank of the Yarra River. Earth spoil from the tunnelling operations will be removed at the Fennell Reserve shaft.
The northern section of the project, around Docklands and the Charles Grimes Bridge, will use pipe jacking technology.
Contractors
John Holland Group has been appointed lead contractor for the project on behalf of Melbourne Water. Other project team members include designer GHD and project manager Connell Wagner.
John Holland managing director David Stewart said “This is the second project to reach the construction stage under John Holland’s six year agreement with Melbourne Water to provide tunnel construction services. We are excited about getting started on this vital piece of Melbourne infrastructure.”
The TBM will be purchased from Canadian company LOVAT. The machinery will take approximately nine months to manufacture, the delivery of the TBM is expected in early 2009.
The Yarra River crossing
Melbourne Water has identified a major component of the MMSR to be the crossing of the Yarra River, upstream from the Charles Grimes Bridge.
The river crossing will be completed by a three stage cofferdam construction, commencing from the south bank and progressing north. The company said that this will ensure two-thirds of the river will remain open to traffic at all times.
The cofferdam construction involves the installation of steel sheet piling to create a closed area in which to work. Some river silt will be removed to allow concrete pipes to be laid under the river bed. Once the silt has been removed, a concrete slab will be poured within the sheet piling as a base upon which a pipe will be laid and fitted together by divers. The pipe will then be encased in concrete, secured into place and back filled to the existing river bed level. The sheet piling arrangement will then be moved further across the river to allow the next stage to be laid.
Melbourne Water said that strict environmental controls in accordance with the Environmental Protection Association of Victoria, Melbourne Water and Parks Victoria requirements will be implemented and maintained throughout the duration of the project to protect the health of the waterways and aquatic life.
Branch sewers
The MMSR project will also involve the construction of approximately 2.5 km of new local branch and reticulation sewers to connect the existing sewer system into the new MMSR. The company said that these works will be undertaken mostly by Trenchless Technology using small diameter pipes between 300 – 500 mm. Small short term shaft sites in local streets will be utilised to complete the works.
Challenges
Melbourne Water has identified a number of interesting challenges presented by the construction of the MMSR. These challenges include working in highly developed urban areas and the multiple major construction projects occurring at the same time, such as the Melbourne Convention Centre and the M1 freeway upgrade. Finally, the crossing of the Yarra River using the staged cofferdam construction will test the ingenuity of the contractors.
Construction begins
Melbourne Water said that construction will begin in August and is expected to be completed by early 2012. The project team will continue to work closely with local residents, community groups and other key stakeholders including the City of Melbourne, City of Port Phillip, VicRoads and Parks Victoria to minimise the potential impacts and ensure regulatory requirements are met.