$1.2 billion wastewater tunnel will drastically reduce overflows into Auckland’s waterways and harbours.
Hiwa-i-te-Rangi, the giant tunnel boring machine (TBM), officially set off on its 14.7-kilometre-long journey under Auckland in July to construct the Central Interceptor, a $1.2 billion wastewater tunnel that will clean up central Auckland’s waterways.
At the bottom of the 40-metre-deep launch shaft, the TBM’s cutterhead began rotating, titanium blades slicing into the earth.
The Central Interceptor is the biggest wastewater project in New Zealand history. Auckland mayor Phil Goff says the super-sized wastewater tunnel will have massive environmental benefits.
“When complete, the Central Interceptor will drastically reduce overflows into our waterways and harbours, improving water quality and creating a legacy of clean, safe, healthy beaches for our children and grandchildren to enjoy,” Goff says.
“By 2025, the tunnel will stop more than 80% of wastewater overflows from the Western Isthmus by storing and conveying flows to the Mangere Wastewater Treatment Plant.”
Hiwa-i-te-Rangi will travel north underground, crossing the Manukau Harbour and finishing its journey in Grey Lynn.
The Central Interceptor tunnel is designed for a 100-year life span to provide for Auckland’s population growth.
The project is being delivered by Ghella Abergeldie JV for Watercare, and between 400 to 600 staff are currently working on eight sites across the city.
Designed and assembled by Herrenknecht AG in Germany, the machine was shipped to Auckland last November.
As the journey progresses, gantries will be added to create a long train with an overall length of 190m. Soil conditions will dictate the TBM’s progress, which is likely to be 12 to 16 metres per day.
Teams of highly skilled operators will work underground. Lasers will guide the route of the TBM so that the direction is millimetre accurate.
An Earth Pressure Balance method of construction is being used. The front of the machine is pressurised to keep groundwater at bay. The TBM is powered by thrust cylinders, which press the cutterhead into the ground.
Most of the spoil will be deposited at nearby Puketutu Island, where Watercare is carrying out a restoration project on a former quarry.
One day the island will be returned to the people of Auckland as a park.
Once completed, the Central Interreceptor will be New Zealand’s longest bored tunnel. Providing storage and conveyance, it will hold 226,000cu m of water — the equivalent of 90 Olympic-sized swimming pools.
