From the magazine, Microtunnelling, Tunnelling

Down and dirty with Lucy Loo

The project presents a range of technical challenges including crossing the Yarra River, tunnelling through variable geology and temporarily by-pass pumping the city’s main sewer in two locations. John Holland is constructing the project on behalf of Melbourne Water. Other project team members include designers GHD, and Project Manager Aurecon.

Managing Director of Melbourne Water Rob Skinner says the original Melbourne Main Sewer was built in the 1890s and needs to be replaced due to its age and capacity.

John Holland Tunnelling Melbourne Main Sewer Replacement (MMSR) Project Manager Nick Lewis, an experienced tunneller, speaks with enthusiasm about the project.

Mr Lewis describes the machinery as “an underground factory – 110 metres long, specially designed to cope with specific ground conditions.”

The area’s geology includes the Quaternary formations comprising Fishermans Bend silt, Coode Island silt and Port Melbourne sand. Coode Island silt is especially notorious as it makes tunnelling very difficult. Extensive planning, including the development of 3D modelling, was completed before the project commenced to ensure both the tunnelling and the wet cofferdam could be completed successfully.

“No one has tunnelled into the Coode Island silts since the 1960s and that was in a compressed air environment – so ours is the first manned tunnel boring machine that has gone into the silts since probably the 1890s,” says Mr Lewis.

Construction update

The site visitors descended the 15 metres at the Fennel Reserve Shaft, boarded the small train and followed the track through the tunnel. Approximately 50 per cent of this section is complete, constructed by the TBM. The machine is tunnelling south to Swallow Street. It will then be reinserted at Fennel Reserve to tunnel north toward the Yarra River.

Tunnelling works were briefly suspended to allow conversation with the team about this interesting project and to experience the tight working conditions underground. As the pipe has an internal diameter of 2.4 metres it was a tight squeeze.

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