Northern Sewerage Project, Stages 1 and 2

The Northern Sewerage Project involves the construction of 12.5 km (8 miles) of new sewer in the Northern suburbs of Melbourne, Australia. The project increases the capacity of the existing sewerage system for Melbourne and in doing so will help to protect local creeks by virtually eliminating sewage spills that can occur after heavy rain.

The two-stage project was developed jointly by Melbourne Water and Yarra Valley Water. Working with Sinclair Knight Merz, Jacobs Associates led the tunnel and shaft design on both stages of the project, and continues to provide construction services through anticipated completion in 2012.

Stage 1 consists of 8 km (5 miles) of gravity sewer pipeline installed in a tunnel and five major work shafts. Tunnel and shaft depths vary from 15 to 60 meters (50 to 200 ft), and the pipeline’s internal diameter ranges from 1.6 to 2.5 meters (5 to 8 ft) to suit hydraulic requirements. Most of the tunneling is encountering weak, interbedded siltstone and sandstone. Excavation is being carried out by multiple tunnel boring machines (TBMs), including earth pressure balance and hard rock TBMs. Initial tunnel support consists of precast segmental lining. The 4.5 km long (3 miles) Stage 2 tunnel has an internal diameter of 1.8 meters (6 ft) at depths ranging from 8 to 35 meters (25 to 115 ft), driven mostly through basalt. Shaft depths range from about 20 to 40 meters (65 to 130 ft), with the main shaft measuring 8.3 meters (27 ft) across. To meet a 100-year design life and address the potential for hydrogen-sulfide-related concrete corrosion, the carrier pipeline for both stages consists of fiber-reinforced plastic pipe (FRPP).

The owners chose a unique procurement method for this project: a form of design-build that shares risks and rewards amongst the Project partners based on their ability to control the work.