Tunnel Boring Machine Hiwa-i-te-Rangi passes three quarter mark for Central Interceptor tunnel

Watch out central Auckland, here she comes! Today, Hiwa-i-te-Rangi our giant Tunnel Boring Machine broke through into a shaft in Western Springs as she builds the 16.2-kilometre Central Interceptor tunnel from Māngere to Point Erin, Herne Bay.

Clouds of dust rose from the 30-metre deep shaft and there were loud bangs as clumps of concrete fell to the floor as the more than five-metre diameter TBM cutterhead broke through at lunchtime. There were cheers from assembled construction crews who watched the action from the surface as the surveying team ensured the TBM ‘s arrival was on target, after travelling 13-kilometres from Māngere.

Photo: Cheers erupted when Hiwa-i-te-Rangi broke through

Chief programme delivery officer Shayne Cunis says the breakthrough has special significance for the whole Central Interceptor project team as Western Springs was the original end point for the tunnel.

“When the Central Interceptor construction contract with Ghella Abergeldie JV was signed in 2019, the tunnel was due to finish at Western Springs. Since then, it has twice been extended all the way to Point Erin. Everyone is to be congratulated on reaching this important milestone in a safe and timely manner. This is a complex engineering project being delivered to the highest standard and we’re another step closer to significantly improving water quality at Tāmaki Makaurau beaches and in waterways by reducing 80 per cent of wet weather overflows.”

Photo: Chief programme delivery officer Shayne Cunis and Ghella Abergeldie JV project director Francesco Saibene amongst the rubble at Western Springs

The Tunnel Boring Machine is currently lying 25m below ground just south of MOTAT. Hiwa-i-te-Rangi began tunnelling in August 2021. Since then, she has crossed under the Manukau Harbour and passed through the 110m-deep Hillsborough Ridge (the deepest section of the route). The 4.5m diameter tunnel has a 1:1,000m gradient, so that wastewater will flow downhill by gravity all the way from central Auckland to Māngere Wastewater Treatment Plant for processing.

Ghella Abergeldie JV project director Francesco Saibene says the successful TBM breakthrough is testament to the skill and expertise of the tunnelling team.

“This is world-class engineering. Infrastructure tunnelling projects of this size and complexity are rare and we are very proud of our team and everything they have achieved.

From here on in, we will continue to encounter favourable ground conditions, helping us to continue tunnelling north safely and efficiently to complete the tunnel by mid-2025.”

Elsewhere on the Central Interceptor project, construction on two link sewers that intersect the main tunnel has been completed. Testing is underway at the new Māngere Pump Station, which will send flows from the tunnel to the treatment plant and the tunnel is being connected to local wastewater networks along the tunnel route. Preparations for excavation of a shaft at the Point Erin site is underway. Section one of the tunnel (from May Rd, Mt Roskill south) will be ready for operation by the end of the year.

The Central Interceptor project is due for completion in 2026.