Auckland’s Underground Giant Emerges After 4 Years of Tunneling

On March 28, 2025, Auckland’s most ambitious underground engineering project reached a historic milestone. After nearly four years of tunneling, the Tunnel Boring Machine (TBM) “Hiwa-i-te-Rangi” broke through at Point Erin Reserve in Herne Bay, completing the 16.2 km-long Central Interceptor wastewater tunnel beneath the city. The moment was met with cheers and pride from over 250 attendees as the massive 5.2-meter cutterhead emerged into daylight—marking the successful end of New Zealand’s longest wastewater tunnel drive.

Launched from the Māngere Wastewater Treatment Plant in July 2021, the TBM traveled under the Manukau Harbour and through ten shafts, laying more than 10,000 concrete rings. Despite navigating complex geological formations—including tunneling 110 meters below the Hillsborough Ridge and just 15 meters beneath the seabed—Hiwa-i-te-Rangi advanced at an impressive 22 meters per day, operating 24/6 without pause.

Constructed by the Ghella Abergeldie Joint Venture, the tunnel is a feat of world-class engineering. As Project Director Francesco Saibene emphasized, this is the longest tunnel Ghella has completed with a single TBM. Even amidst the challenges of the COVID-19 pandemic, labor shortages, hyperinflation, and severe weather events, the project was completed safely, economically, and on time.

The tunnel’s interior features thermally welded, plastic-lined rings to withstand the corrosive effects of wastewater, ensuring durability for over a century. Soon, the TBM will be dismantled and removed, and the tunnel connected to the wider wastewater network.

Already, the southern half of the tunnel is operational, directing combined stormwater and wastewater flows to Māngere’s upgraded treatment plant. When the entire system is completed in 2028, it will reduce wet weather overflows by 80%, drastically improving water quality in local streams and beaches.

The Central Interceptor also sets the stage for future infrastructure: a new Huia Water Treatment Plant and upgrades to the Māngere facility are next. These investments not only address current needs but fortify Auckland’s infrastructure for generations to come.