Sunday, June 16, 2024

‘Piper’ Completes Outfall Project

Completing the 845 m of tunnelling, and installing the 832 m steel outer casing for the wastewater pipeline in just over one month

McConnell Dowell recently announced that ‘Piper’, the microtunnel boring machine (MTBM) and the team have completed tunnelling on the West Coast of New Zealand’s South Island for the Westland Milk Products Marine Outfall project.

Piper was fresh from another McConnell Dowell tunnelling project (the Snells Algies Ocean Outfall project) in the North Island, where the team set a new world record of 2,021 m for the longest single drive by a Direct Pipe® MTBM earlier this year.

The project team used this world leading experience, completing the 845 m of tunnelling, and installing the 832 m steel outer casing for the wastewater pipeline in just over 1 month, two weeks ahead of the construction programme.

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The Direct Pipe® tunnelling method was chosen to mitigate the impact of work on the delicate coastal ecosystem. The scope of the works included:

  • Constructing a 60 m long, 6 m wide and 7.5 m deep sheet piled MTBM launch trench.
  • Completing an 845 m microtunnel Direct Pipe®
  • Installing 832 m of steel casing pipe through the Direct Pipe® thrusting technique that remains buried and submerged at the seaward end.
  • Slip-lining installation of an HDPE carrier pipeline into the steel casing pipe.
  • An ocean recovery of the MTBM followed by installation of the marine diffuser.
  • Construction of an onshore de-aeration chamber and carrier pipe connections.

To retrieve the MTBM, specialist excavation equipment sourced from Malaysia was to be used to expose Piper under the seabed. A dive team would then disconnect Piper and tow her to Greymouth Port where she would be lifted from the water.

Once complete this project will be the first ocean outfall on the West Coast of the South Island and will provide a new ocean discharge point for the treated wastewater from the Westland Milk Products facility. Final marine operations are expected to be completed in early 2021. Website:

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