Beneath the Yarra - Duplicating the Hobsons Bay Main Sewer

Abstract

The construction and commissioning of Melbourne Water’s Hobsons Bay Main Sewer Duplication Project was completed in October 2024. The new 678-metre siphon sewer, constructed underneath the Yarra River between Westgate Park, Port Melbourne and Scienceworks in Spotswood, now transfers 30% of Melbourne’s wastewater to the Western Treatment Plant in Werribee. The duplication of the sewer main has enabled service delivery partners, John Holland, to commence the trenchless rehabilition of the existing 605m sewer to cater for Melbourne’s future growth and demand. A risk-based approach to design and construct the new sewer was required to address the challenging ground conditions at the launch and retrieval sites, and along the tunnel alignment including the river crossing. Substantial ground improvement works were required for shaft excavations and the mined tunnel between the new and existing sewers. This paper will explore the tunneling and pipe-jack operation in soft ground up to 27 metres below the water table, constructing shafts over critical live sewers in soft saturated soil and completing live connections into the sewer network.