Engineering a Sustainable Underground Wastewater System
Beneath the bustling streets of Auckland, an engineering marvel is quietly taking shape. The Watercare Central Interceptor Project, New Zealand's largest wastewater initiative, is reshaping the city's relationship with its waterways. This groundbreaking endeavor aims to reduce wastewater overflows during heavy rain events by up to 80%, providing a long-term solution to one of the region's most persistent environmental challenges.
At the heart of this transformation lies a 16.2-kilometer main tunnel and two link sewers measuring 1.1 and 3.2 kilometers in length. The construction consortium Ghella Abergeldie JV deployed two state-of-the-art Herrenknecht tunnel boring machines (TBM), with shield diameters of 5,450 millimeters and 2,830 millimeters, to excavate these three vital passages. Both Earth Pressure Balance Shields (EPB Shield) completed their journey after operating with precision in Auckland's complex geological environment.
Hiwa-i-te-Rangi’s Historic Journey to Carve Out the Main Tunnel
The star of the project is undoubtedly Hiwa-i-te-Rangi (Herrenknecht EPB Shield), a 190-meter-long, 740-tonne behemoth whose name translates to “Star of the Sky” in Māori. The German-engineered machine tackled complex geology - including silty sandstones, mudstones, and volcanic basalt - along its entire route from Pt Erin in Herne Bay to the Māngere Wastewater Treatment Plant, 15 to 110 meters beneath Auckland's surface.
Tunnellers from the Ghella Abergeldie JV worked 24 hours a day, six days a week to construct the main tunnel with its 4.5-meter internal diameter, maintaining an impressive average advance rate of approximately 22 meters per day.
On March 28, 2025, Hiwa-i-te-Rangi completed its epic journey after Auckland Mayor Wayne Brown gave the final command for the TBM to start up for the last time to break through the final centimetres of the tunnel. This historic moment, marking the successful fulfilment of a project that began with the machine's launch in July 2021, was celebrated by 250 guests.
The Supporting Act: Domenica’s Precision Performance
While Hiwa-i-te-Rangi was excavating the main tunnel, the smaller but equally important micro TBM Domenica was completing Link Sewers B and C at depths ranging from 12 meters to 70 meters. This 2.83 meter diameter Herrenknecht EPB Shield was named in honor of two important women in the contractor's Ghella family, which dates back 150 years. Using pipe jacking technology, Domenica installed six tunnel sections totaling 4.3 kilometers. The longest drive reached 1,187 meters between Dundale and Miranda Reserve.
The Central Interceptor project demonstrates how major infrastructure can be both functional and forward-thinking. It is expected to significantly improve the water quality of Auckland's beaches and other waterways. Infrastructure constructed by these powerful TBMs is strong and reliable and is set to last at least 100 years. With the final breakthrough of the Central Interceptor main tunnel, Auckland is setting a new standard for sustainable urban water management.
