Working together to keep major sewer online during construction

In any major transport development, there are many hidden components that the average person does not think about. It’s why working together is so important for utilities of all sorts.

In any major transport development, there are many hidden components that the average person does not think about. It’s why working together is so important for utilities of all sorts.

“When we think of major infrastructure projects like the Metro Tunnel, the focus often lies on the tracks being laid and the new stations being built,” Senior Project Manager, Major Infrastructure Projects at Melbourne Water Mark Coffey said. “However, behind the scenes, essential work performed by water statutory authorities is crucial to completing these projects.

“We’re not there to cut the ribbon when the station opens, but our work during the construction phase to manage flood risks, relocate water infrastructure and keep essential water services running is critical.”

The Metro Tunnel represents the most significant enhancement to Melbourne’s train network since the City Loop was launched in 1981. Scheduled to open in 2025, it will link the bustling Sunbury, Cranbourne and Pakenham train lines via a new tunnel under the city.

The new Metro Tunnel features twin 9-kilometre rail tunnels connecting the city’s west to the southeast and five new underground stations at Arden, Parkville, State Library, Town Hall and Anzac. This project will effectively double the extent of Melbourne’s underground rail network, with some stations situated as much as 40 metres below street level.

The success of an infrastructure project of such a massive scale hinges on the seamless collaboration between various agencies, including statutory authorities such as Melbourne Water.

“As the massive machines used to dig the tunnel made their way underneath our bustling metropolis, a complex network of essential underground infrastructure lay in their path requiring spectacular feats of engineering, structural science and geoscience to move them,” Coffey said.

The critical link 

The partnership and collaboration between Melbourne Water and the Metro Tunnel construction teams highlights the significance of coordinated planning in urban development, where transportation, water management and environmental considerations need to collaborate effectively.

A prime example is Melbourne Water’s South Yarra Main Sewer, which was relocated to exacting criteria to accommodate the new Anzac Station on St Kilda Road. Many options were considered on how the new 1.8m sewer would be relocated yet remain fully operational and durable for the next 100 years.

When the first people step onto the platform of Anzac Station, located 22 metres under St Kilda Road near the Shrine of Remembrance, few will realise that one of the city’s main sewers – the 115-year-old South Yarra Main Sewer – is just metres away and needed to be moved to allow the station and the rail tunnel to be built.

The South Yarra Main Sewer is crucial to Melbourne’s wastewater management system. This extensive pipeline runs from South Yarra to Hawthorn, facilitating wastewater transport from numerous southeastern suburbs of the metropolitan areas.

“Relocating the main sewer was no minor task,” Coffey said. “It required meticulous planning and execution. The sewer could not simply be shut down for the duration of the relocation – doing so would have risked significant disruptions to the wastewater system.”

Feats of engineering 

“The construction was akin to performing open-heart surgery while the patient remained awake, a delicate operation that required precision and expertise,” he said.

Melbourne Water provided exacting design criteria to ensure the sewer’s ongoing functionality during relocation. The project constructors employed advanced engineering techniques and technologies. John Holland led the initial relocation of the sewer in late 2017, and the major station and ‘build around’ continued under the project’s major contractor, the Cross Yarra Partnership.

Works involved lowering existing drains and constructing new sections of the trunk sewer that would seamlessly integrate with the ongoing works for the Anzac Station. Using methods such as pipe jacking and trenchless technology minimised the disruption to the surrounding environment and communities. Panels of Diaphragm Walls (the future cavern of the Anzac Station) were driven on either side and over the relocated sewer, allowing an excavation that eventually exposed the sewer and prepared it for a protection shell to be encased around it. This arrangement virtually fused the sewer to the station’s foundations, eliminating any effects of ground movement. The sewer is protected by the surrounding area being ‘pin-cushioned’ with many tension piles.

This allowed the sewer to remain operational and ensured that construction timelines for the new station were adhered to, helping to keep the entire project on schedule.

Paving the way

Ultimately, while Melbourne Water may not be the agency cutting the ribbon at the grand opening of the Anzac Station, its contribution was pivotal to the project’s success. The relocation of the South Yarra Main Sewer is a testament to the intricate and often unseen work that goes into major infrastructure projects and the essential role that water authorities play in urban development.

As cities grow and evolve, the collaboration between transport agencies and water authorities will be more critical than ever. By working together, they can ensure that infrastructure projects meet current demands and pave the way for a sustainable and resilient future.

For more information, visit melbournewater.com.au

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