New tunnel boring machine arrives for outfall pipeline project at Army Bay Wastewater Treatment Plant


A new tunnel boring machine (TBM) has arrived at Army Bay, Whangapararoa, to help install a new outfall pipeline, as part of $31 million upgrades to the Army Bay Wastewater Treatment Plant.

The current pipeline is nearing the end of its operational capacity and needs to be replaced with a larger pipe. The new infrastructure will ensure greater reliability and resilience of the treatment plant as the Whangapararoa region expands. Treated wastewater discharge volumes at the plant will quadruple, from 350 litres per second to 1,400 litres per second.  

The state-of-the-art $6.2 million micro TBM has been imported from Germany and will use a ‘direct pipe’ method of tunnelling, which means sections of steel pipe will be thrust into place. The 2km route will start at the treatment plant and end at the foreshore. A further 900 metre HDPE pipe section with concrete footings, will then be floated into place and rested on the seabed.

Watercare project manager, Dirk du Plessis believes this is a record- breaking effort: “This is the first time that this direct pipe method is being used in New Zealand and a 2km thrust will be a world record.

"There are many advantages to using this type of construction, which is safer for workers, produces less dust and has less impact on the environment than open-cut methods — which is particularly important as the site lies within the Shakespear wildlife sanctuary.”        

The TBM has been given a name, as is the tradition in the construction industry (‘Alice’ was the name of the enormous Waterview TBM). Earlier this year, project staff from Watercare and contractor McConnell Dowell were given a shortlist of proposed names and then voted for their preferred option. ‘Blanche’ was the name chosen and recognises the matriarch of the Shakespear family, after whom the nearby reserve land is named.