On 28 March 2025 the TBM Hiwa-i-te-Rangi broke through into a 30-metre- deep shaft at Point Erin Reserve, Herne Bay completing the 16.2-km Central Interceptor wastewater tunnel running under Auckland: click here for a video. 

The TBM - 200 m-long with a 5.2 m diameter - started its journey from Māngere Wastewater Treatment Plant in July 2021, travelled under Manukau Harbour, across the city and laid more than 10,000 rings to build New Zealand’s longest wastewater tunnel. Tunnelling has taken place 24-hours per day, six days per week. She has laid eight to 10 rings and travelled around 22-metres per day. The concrete rings are coated with a plastic liner to protect against the corrosive effects of wastewater, to ensure the tunnel lasts 100 years. 

The Ghella Abergeldie Joint Venture had a number of challenges to overcome including crossing the Manukau Harbour and tunnelling just 15-m below the seabed, as well as tunnelling 110-m deep below the Hillsborough Ridge, Mount Roskill. 

Now that tunnelling is complete, the TBM cutterhead will be dismantled and lifted from the shaft in section. The tunnel segments will be thermal welded to ensure an airtight seal, services such as locomotive tracks will be removed, the new tunnel will be connected to the existing Auckland’s wastewater network. 

For further information click here and nz/18 for the tunnelbuilder archive. Visit https://www.watercare.co.nz/, https://www.ghella.com  and  https://abergeldie.com/. 15/25.