McConnell Dowell is proud to announce that ‘Piper’ the micro tunnel 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 (Snells Algies Ocean Outfall project) in the North Island, where the team set a new world record of 2,021m for the longest single drive by a Direct Pipe® MTBM earlier this year.

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

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

The scope of the works includes:

  1. Constructing a 60m long, 6m wide and 7.5m deep sheet piled MTBM launch trench.
  2. Completing an 845m micro tunnel Direct Pipe® drive.
  3. Installing 832m of steel casing pipe through the Direct Pipe® thrusting technique that remains buried and submerged at the seaward end.
  4. Slip-lining installation of the HDPE carrier pipeline into the steel casing pipe.
  5. An ocean recovery of the MTBM followed by installation of the marine diffuser.
  6. Construction of an on-shore deaeration chamber and carrier pipe connections.

To retrieve Piper the MTBM, specialist excavation equipment sourced from Malaysia will be used to expose Piper under the seabed. A dive team will then disconnect Piper and tow her to Greymouth Port where she will 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 will be completed in early 2021.