From the magazine, Microtunnelling, Tunnelling

Tunnelling success in Melbourne

The Melbourne Main Sewer Replacement (MMSR) involves the construction of approximately 2.3 km of new sewer in and around inner-city Melbourne.

The new sewer, which begins in the Docklands precinct, crosses the Yarra River upstream of the Charles Grimes Bridge and continues into Port Melbourne, is being built with the assistance of a specially-designed tunnel boring machine (TBM).

The MMSR is an important project for the city that will deliver health and environmental benefits to meet the future growth of Melbourne.

Major developments

2010-11 has seen many significant advances made on the project. The 140 m, on-grade crossing of Melbourne’s iconic Yarra River was completed in February this year, following the installation of the final section of 2.4 m diameter pipeline. Construction was undertaken in three stages to ensure the Yarra River remained open to river users for the duration of works. Specialist divers worked in zero visibility conditions, installing sections of the pipe within a wet cofferdam.

Another major development occurred in April 2011, when the project’s 164 tonne, 93 m TBM completed the final section of tunnel to emerge at the South Wharf shaft site in the Docklands area. This second and final major tunnel drive on the project marked the completion of over 18 months of tunnelling under Melbourne’s inner suburbs.

Project challenges

At the project’s beginnings in 2005, Melbourne Water, together with project partners, contractor John Holland, designers GHD and project manager Aurecon, knew that the MMSR would not be without its challenges.

“The 875 m final tunnel drive was one of the most challenging engineering feats of the project due to difficult geological conditions, which saw the specially designed Earth Pressure Balance (EPB) TBM steered through soft clay-like Coode Island Silt, and around critical infrastructure, including the M1 Freeway,” said Melbourne Water Project Director Phil Corluka.

“In undertaking these essential replacement works, the MMSR team has developed a good understanding of geology and hydrogeology, being the first to mechanically tunnel through the Yarra Delta, their most notorious being the Coode Island Silt, which provided significant challenges to the original constructor in the 1800s. The learnings gathered on this historic project provide fantastic knowledge for future projects and for soft ground tunnelling as a whole.”

In addition to two major tunnel drives and a river crossing, the MMSR also encompasses the construction of 1.9 km of localised branch and reticulation sewers. To minimise impacts on the local community, Trenchless Technology has been effectively utilised to install smaller reticulation pipes ranging in diameter from 300-500 mm. Smaller shaft sites, situated within densely populated suburban streets, have been used to complete this intricate set of works.

Vital infrastructure

The MMSR is an important project that will deliver health and environmental benefits to meet the future growth of Melbourne. The new sewer will have three to four times the capacity of the existing sewer and will service the CBD and the fast growing Docklands precinct, which is expected to be home to 20,000 residents, and workplace for 25,000 in 15 to 20 years' time.

The MMSR is currently tracking ahead of schedule, under budget, and has successfully overcome many challenges encountered throughout construction. Early identification and mitigation of these challenges has been paramount in achieving many milestones on the project. Identifying potential risks and issues has been fundamental in planning for both the successful completion of construction, and the quality of the final product, which will service the city of Melbourne for another century.

Looking ahead

With fresh climate extremes breaking records in 2010-11, the importance of a robust network of water supply, drainage and sewerage infrastructure has become clearer than ever. Mr Corluka said that as Melbourne Water works towards the completion of the MMSR, and looks ahead to the next infrastructure installation and rehabilitation projects, Trenchless Technology will continue to assist in the delivery of their works.

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