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Central Interceptor project extended

An extra 1.5 km has been added to the Central Interceptor project as Watercare’s massive tunnel boring machine reaches Manukau Harbour.

The TBM will bore a 1500 m stretch at depths of 15 to 20 metres beneath the seabed as it crosses the harbour.

It is a big task ahead of the tunnelling crews, with safety front and centre in the minds of all involved. Potential hazards include fire and water ingress, but the tunnel includes two refuge chambers – that provide shelter in case of emergencies – and workers carry backup breathing apparatus with them when in the tunnels.

Head of health, safety and wellbeing Bronwyn Struthers says that the safety measure do not stop there.

“We built a dedicated training centre and everyone undergoes a two-day induction programme, as well as regular underground training. We even imported a section of a real TBM so tunnellers could practise replacing the cutterhead tools and climbing into a decompression chamber,” said Struthers.

“We are also the only project in New Zealand to introduce a card identification system, which indicates where workers are located, should they become incapacitated.”

The TBM has also undergone some changes in preparation for the crossing, according to executive program director Shayne Cunis.

“In recent days, Hiwa-i-te-Rangi has been checked thoroughly, including the cutterhead. More than 30 ‘cutting discs’ have been swapped for ‘rippers’ for maximum efficiency as she powers her way through East Coast Bays Formation rock all the way to Grey Lynn,” Cunis said.

Having tunnelled 2.5 km since it started in August 2021, workers now have to reach the TBM by taking a small locomotive to the work site.

Extending the project
Originally Watercare had a planned program of work that would separate the combined stormwater/wastewater network in St Marys Bay and Hearne Bay – a targeted effort to reduce rain-related overflows into the harbour and improving water quality.

However, increases in material, labour and traffic management costs, combined with further costs to accommodate geotechnical risks identified during the design stage, more than double the estimated overall cost – from $136 million to $278 million.

Chief executive Jon Lamonte said that extending the Central Interceptor will achieve the same results sooner than the original plan, and at about 20 per cent lower cost.

“We’d be almost eliminating overflows at these city beaches by 2028. It would also mean there’d be less disruption in the St Marys and Herne Bay communities from construction activity and traffic… construction activity would be localised to the Pt Erin drop shaft,” said Lamonte.

Watercare and Healthy Waters are engaging local community liaison groups and mana whenua about the alternative approach.

Extending the tunnel to Pt Erin is expected to add another three or four months to Central Interceptor project, which is currently scheduled to finish in mid 2026.


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