Giant boring machine breaks through after 4-year dig under Auckland, New Zealand

(UI) — A 200-meter-long tunnel boring machine (TBM) named Hiwa-i-te-Rangi completed a major milestone on March 28, breaking through at Point Erin Reserve in Herne Bay and finishing Auckland’s 16.2-kilometer (10-mile) Central Interceptor wastewater tunnel.

Auckland Mayor Wayne Brown initiated the final push of the TBM, which launched from the Māngere Wastewater Treatment Plant in July 2021. The TBM, built by Herrenknecht AG in Germany, has now completed the longest wastewater tunnel in New Zealand, laying over 10,000 concrete rings beneath the city and Manukau Harbor.

More than 250 guests watched the breakthrough live, cheering as the 5.2-meter-diameter cutterhead emerged through a shaft wall amid clouds of dust.

"This is world-class engineering, and it’s been completed safely, economically, and on time — which is rare for any major infrastructure project," said Shayne Cunis, chief program delivery officer. He credited the 600 staff members and tunneling crews from the Ghella Abergeldie Joint Venture, who worked around the clock, six days a week.

The breakthrough marks the final of ten shaft connections for the TBM, which tunneled beneath significant geological challenges — including 15 meters (49 feet) below the seabed and 110 meters (361 feet) deep below Hillsborough Ridge and Mount Roskill.

“This is the longest tunnel our company has ever constructed with a single TBM,” said Francesco Saibene, project director with Ghella, the 130-year-old Italian tunneling company. “We did all this despite the COVID-19 pandemic, skills shortages, hyperinflation, and major storms.”

Students from local schools named the TBM Hiwa-i-te-Rangi after a star in the Matariki cluster, in line with the tradition of giving TBMs female names. The TBM laid between 8 to 10 rings per day and advanced approximately 22 meters (72 feet) daily. The tunnel’s concrete rings are coated in plastic to resist wastewater corrosion, with a design life of 100 years.

Now that tunneling is complete, the TBM will be dismantled and lifted out in sections. Crews will weld thermal seals on segment joints and remove temporary elements like locomotive tracks. The tunnel will be progressively integrated with Auckland’s wastewater network.

The southern portion of the tunnel—from Blockhouse Bay southward—went live in February. A new pump station at Māngere is already directing combined stormwater and wastewater flows from the tunnel to the treatment facility.

Once the entire project, including work in Herne Bay, is completed in 2028, it is expected to reduce wet weather overflows into local streams by 80% and improve water quality at Auckland’s beaches. It will also help accommodate future population growth and improve system resilience.

Future investments
Watercare’s 10-year business plan, released in March, outlines future major projects that will follow the Central Interceptor.

In west Auckland, the aging Huia Water Treatment Plant will be replaced with a facility capable of producing 160 million liters (42 million gallons) per day. The plan includes building new watermains and two large storage reservoirs.

Another major investment will focus on upgrades at the Māngere Wastewater Treatment Plant, which currently serves 75% of Auckland’s population. Equipment and processes will be improved to maintain compliance with discharge standards and protect Manukau Harbor.

“With dozens of treatment plants, hundreds of pump stations, and thousands of kilometers of pipe, we must maintain assets from as far south as Waiuku to as far north as Wellsford,” said Watercare CEO Dave Chambers. “Over the next 10 years, we will be working in every community.”

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