Giant boring machine lowered to dig the longest underground wastewater tunnel in NZ

Wednesday, 23 June 2021

Tunnel Boring Machine, Hiwa-i-te-Rangi is lifted down a 40m shaft to begin construction on the country's longest bored tunnel.

Watercare’s $1.2 billion dollar project for the longest underground wastewater tunnel in Auckland has begun.

A giant tunnel boring machine was lowered 40 metres down a shaft by crane, below sea level at the Māngere pump station on Tuesday afternoon.

The machine will be used for the Central Interceptor project to build a 14.7 kilometre wastewater tunnel from central Auckland suburb, Grey Lynn to a wastewater treatment plant in Māngere.

The tunnel will reduce wet-weather overflows from central Auckland waterways and beaches caused by stormwater during heavy rain whilst also adding capacity to the supercity’s growing population.

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The $1.2 billion dollar project for New Zealand’s longest underground wastewater tunnel is set to begin construction.

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Once completed, the Central Interceptor will be the longest bored tunnel in the country, holding up to 226,000 cubic metres of water. It will also act as a buffer for Māngere treatment plant in times of high flow.

The wastewater tunnel will help reduce the overflow of wasterwater in Auckland waterways and beaches.

The excavated earth will be deposited at Puketutu island, where Watercare is carrying out a restoration project to create a park.

Watercare traditionally names tunnel boring machines female names and named the machine Hiwa-i-te-Rangi, after the Matariki star.

Hiwa-i-te-Rangi will be cutting through a concrete wall and as the tunnel progresses, gantries will be added, with an overall length of 190 metres.

Lasers will be the guide for the machine, meaning the cut and direction will be accurate by the millimetre.

Digging for the tunnel will begin at the end of July, creating a tunnel travelling underneath the Manukau harbour towards central Auckland.

In the meantime, the tunnel boring machine will be assembled underground and go through testing.

The Central Interceptor project beginning at Māngere pump station will also connect two new link sewers in Mt Albert, Mt Roskill and Blockhouse Bay.

“We wish her well as she begins this exciting journey,” said Shayne Cunis, Watercare Central Interceptor executive programme director.