How will the project be completed?

  • A new 1.2 kilometre gravity sewer will be built to divert sewage flows from the MRM Sewer into the larger North Western Sewer in Maidstone, which transports wastewater to the Western Treatment Plant.
  • The new sewer will connect from the MRM Sewer on the northern side of the Maribyrnong River, crossing the river via a new pipe bridge, with a buried sewer to be constructed from Medway Golf Course to Hampstead Road.
  • Over 800 metres of the new sewer will be constructed by a tunnel boring machine (TBM) under Williamson Road. The sewer will be located at depths of up to 30-40m below ground.
  • The remaining section of the new sewer will be constructed by open-cut trenching methods at a depth of 2-4 metres below ground.
  • As part of this project, we're working with Maribyrnong City Council to open up an inaccessible section of land between Medway Golf Course and the Maribyrnong River for the community to enjoy continuous views and access along the river.

Project map

Project location map showing alignment of new sewer

Constructing the new sewer with a tunnel boring machine (TBM)

We’ll be using a ‘pipe jacking’ TBM to construct the main length of the new sewer. Force is applied to push the new sewer pipe through the ground while controlled excavation takes place at the face of the TBM.

The process involves:

  • Excavating an entry pit (called a ‘launch shaft’) and an exit pit (called a ‘retrieval shaft’) at the beginning and end of the sewer tunnel alignment (these shafts will later become maintenance holes). The pits are large enough to accommodate the tunnelling equipment and construction personnel.
  • Once the pits are excavated, the hydraulic jacking rig is put into position and the TBM is lowered into the entry pit in segments and assembled underground to form the full machine.
  • The hydraulic jacking rig applies a force that pushes the TBM through the wall of the entry pit and into the ground. Once the TBM reaches a pre-determined position, a segment of pipe is lowered into the entry pit and the jacking rig pushes the pipe behind the TBM.
  • The jacking rig continues to apply force, pushing both the pipe and TBM forward on their way to the exit pit.
  • Excavated material (soil, rock and water) is moved through the TBM to the surface, where it is separated and removed from site by trucks.
  • This process continues, with several pipe segments being jacked in sequence until the TBM reaches the exit pit, where it is disassembled and lifted from the shaft.