The tunnelling work on Auckland’s Central Interceptor reached a significant milestone today, with the breakthrough of the Tunnel Boring Machine (TBM) Hiwa-i-te-Rangi into a shaft at Point Erin Reserve, Herne Bay.
Launched from the Māngere Wastewater Treatment Plant in July 2021, the TBM has completed a 16.2-kilometre journey, marking the completion of New Zealand’s longest wastewater tunnel.
The 200-meter-long Herrenknecht TBM travelled beneath the Manukau Harbour and through the city, laying more than 10,000 concrete rings. These rings were installed to create a protective layer against wastewater’s corrosive effects, ensuring the tunnel’s durability for over a century. On average, the TBM laid eight to ten rings per day, advancing about 22 meters daily.
Shayne Cunis, Chief Programme Delivery Officer, called the breakthrough a monumental achievement, highlighting the expertise of the tunnelling team from the Ghella Abergeldie Joint Venture.
“The team worked tirelessly 24 hours a day, six days a week, to complete the tunnel. This is a remarkable example of world-class engineering, and it has been finished safely, on time, and within budget—an achievement that is rare in major infrastructure projects,” said Cunis.
Despite having passed through 10 shafts, he noted, “Breakthroughs never get old, and we’ll always remember this final one. I am immensely proud of the 600 staff who contributed to this project. Today is truly special.”
Francesco Saibene, Project Director for Ghella Abergeldie, explained that the Central Interceptor was the longest tunnel the company had built with a single TBM. He also noted the project’s global significance, given the technical challenges it presented.
“We faced several obstacles, including tunnelling under the Manukau Harbour just 15 meters beneath the seabed, as well as reaching depths of 110 meters below the Hillsborough Ridge in Mount Roskill. Despite challenges like the Covid-19 pandemic, skill shortages, inflation, and major storms, our team persevered,” said Saibene.
This is Ghella’s first project in New Zealand, and the company has committed to remaining in the country after the government’s recent infrastructure investment summit.
In the coming weeks, the TBM Hiwa-i-te-Rangi will be removed from the shaft, and work will continue to connect the tunnel to the existing wastewater network.
Last month, the southern portion of the tunnel from Blockhouse Bay to the south went live. A new pump station at Māngere now transports combined stormwater and wastewater flows from the tunnel to the treatment plant for processing.
Upon the completion of the NZ$1.6 billion project and the associated work in Herne Bay in 2028, the Central Interceptor will reduce wet weather overflows into streams by 80% and improve water quality at nearby beaches. The project will also support future urban growth and enhance the resilience of the wastewater network.