Central Interceptor Pivotal Milestone: Hiwa-i-te-Rangi Breaks through at May Road B Shaft
Jacob Liu, CPEngProject Structural Engineer
Sean Peterfreund, CPEngSenior Associate
Watercare’s Central Interceptor is a major upgrade to Auckland's wastewater system and, upon completion, will be the largest wastewater infrastructure project in New Zealand's history. This $1 billion, 14.7-kilometer-long (9.1 mi) deep sewer tunnel will convey and store wastewater from the city’s combined sewer network. The project addresses aging and vulnerable assets, accommodates growth, and mitigates wet weather overflows into Waitematā and Manukau Harbours. The system will store peak wet-weather flows, facilitating controlled delivery to the Māngere Wastewater Treatment Plant.
As part of the Jacobs team, Delve Underground has been the owner's designer for tunnels and shafts for nine years and has been providing construction phase services (CPS) since construction began in 2019. The project’s main contractor is the Ghella Abergeldie Joint Venture.
Recently, the Central Interceptor project achieved a significant milestone as the Hiwa-i-te-Rangi* tunnel boring machine (TBM) reached the halfway point of its 14.7-kilometer journey. This occurred when the TBM broke through into work shaft B at May Road, Mount Roskill. This marks the completion of Stage 1 tunneling.
May Road Shaft B, located at the midpoint of the entire tunnel, has an internal diameter of 10.8 meters (35.5 ft) and an invert depth of 69 meters (226.5 ft). As the designer of permanent shaft lining structures, Delve Underground worked closely with Watercare for construction monitoring during the 12-month construction before the TBM breakthrough. The completion of both the wall lining and the TBM breakthrough at May Road B Shaft marks a significant project advancement. This achievement underscores the project's focus on innovation, sustainability, and dedication to responsible urban development. The wall lining fortifies the shaft's structural integrity, ensuring its durability in a corrosive wastewater environment and optimal performance for a century to come.
Following the significant accomplishments at May Road B Shaft, and after a pause to relocate tunneling operations from Māngere to May Road, Hiwa-i-te-Rangi will restart its journey for the second and final stage of the main tunnel to the Central Auckland suburb of Grey Lynn. Meanwhile, other construction activities have shifted to the Māngere Pump Station site and Western Springs site, specifically to the development of confluence chambers, a diversion chamber, and various shaft undertakings.
This milestone exemplifies the project's resilience in the face of challenges such as Covid-19 lockdowns, closed borders, global shipping delays, and major weather events. Despite these obstacles, the project remains on track for completion in 2026 as planned, with a strong focus on safety.
*One of the sacred stars of the Kāhui o Matariki (Pleiades star cluster), an important part of the Māori culture.