Watercare’s Hiwi-i-te-Rangi giant Tunnel Boring Machine (TBM) has today (4 September) broken through into a shaft in May Road, Mount Roskill marking the halfway point of her 14.7kilometre journey to central Auckland as she creates the Central Interceptor tunnel.

Hiwa-i-te-Rangi Tunnel Boring Machine breaks through into May Rd, Mt Roskill shaft marking halfway point of her almost 15-kilometre journey to central Auckland to build the Central Interceptor pipe

There were loud cheers from assembled construction crews as the more than five metre diameter cutterhead ground through a 69m deep shaft wall. The tunnel will run from Māngere Wastewater Treatment Plant to Grey Lynn and will be intersected by two link sewers. The Central Interceptor project is the largest wastewater infrastructure project in New Zealand history and will significantly clean up wet-weather overflows into waterways and the Waitematā Harbour.

Watercare Central Interceptor executive programme director, Shayne Cunis says the breakthrough marks an important milestone, which been achieved despite significant challenges: “We all deserve to savour this moment. We’re on track to deliver this project in 2026 as planned despite everything that has been thrown at us—COVID-19 lockdowns, closed borders, global shipping delays and major weather events. But most importantly, the project is being delivered safely.

“I want to pay tribute to our Ghella Abergeldie JV construction partners, as well staff from Jacobs, AECOM, Delve Underground, Watercare and our sub-contractors, who are all working so hard to deliver this project in the best way we can. This is our busiest year, with around 600 staff working on 16 sites. We’ve tunnelled under the Manukau Harbour, we’ve passed 110m under the Hillsborough Ridge, we’ll keep our heads down and keep going until we reach central Auckland.”

Ghella Abergeldie JV project director Francesco Saibene also praised his tunnelling team: “We have worked very hard to achieve this milestone. The Central Interceptor will be the longest bored tunnel in New Zealand and reaching the halfway mark is a moment for us all to celebrate.

Crossing the Manukau Harbour from Māngere Bridge to Hillsborough in 2022, was the highlight of our journey so far. Undersea tunnels are rare in New Zealand and the 1500m stretch was completed in just 11 weeks. We are very proud this complex engineering feat was achieved smoothly and safely.

The Central Interceptor project has seen a flurry of milestones. The December 2022 undersea crossing was followed in March this year by completion of the first link sewer, to collect flows from Mt Roskill and Blockhouse Bay. Construction has started on a second link sewer, which intersects the main shaft in Wairere Ave, Mt Albert and will be completed in two drives.

Meanwhile, work is progressing well on the Māngere Pump Station, adjacent to the treatment plant. Inflow pipes are being installed and six pumps are being installed, to send flows from the main tunnel to the treatment plant for processing. Section one of the main tunnel (running from May Rd south) and both link sewers are due for commissioning by mid-2024. Shayne Cunis says getting the first section up and running will take pressure off the aging Western Interceptor: “Resilience has always been a key driver for the project, along with providing for future growth and environmental benefits. Once section one goes live, our Watercare operations teams will be able to do essential maintenance on the Western Interceptor.”

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