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Army Bay WWTP Outfall Project - Record Breaking Innovation

The Army Bay Wastewater Treatment Plant (WWTP) and Outfall Pipeline service the peninsula of Whangaparaoa, North of Auckland and the surrounding Orewa Region. Similar to other parts of Auckland, this region has experienced extensive growth and the existing aging pipe was starting to struggle with the flows. To manage current and enable future growth Watercare required a new outfall within the Shakespear Regional Park (SRP) – a sanctuary for native species surrounded by a large pest-proof perimeter fence and sea, across Watercare and New Zealand Defence Force (NZDF) land.

The challenge was to install the new outfall with minimal impact on the local flora and fauna, which included newly released Kiwis, and accommodate an NZDF training facility, which included live-firing ranges located between the treatment plant and the outfall location.

Watercare Services Ltd awarded the contract to McConnell Dowell Constructors Ltd based on a proposal to utilise an innovate tunneling technique called Direct Pipe®. The Direct Pipe® method was developed by Herrenknecht in 2007, and had never before been used in the Southern Hemisphere before. On completion, the team set a world-record for the longest Direct Pipe® drive at 1,929 m, surpassing the previous record of 1,495 m set in Texas, US in 2017

In addition to the challenge of learning to operate a new machine and push it to new boundaries, the construction team had to install over 900m of 800mm High Density Polyethylene Pipe (HDPE) pipe in the fast flowing Tiritiri Maitangi channel, retrieve the Direct Pipe® machine from its seabed breakthrough point and slip line 1,929m of 1,100mm HDPE pipe in single push.

This paper outlines the trials that the Watercare Services Ltd and McConnell Dowell Constructors Ltd team overcame to successfully complete this high-risk project with no injuries, within the Watercare budget and on time.