Photo: TBM, Hiwa-i-te-Rangi, is lifted into a launch shaft at our Central Interceptor site in
The first section of a Tunnel Boring Machine (TBM) called ‘Hiwa-i-te-Rangi’ has this afternoon (22 June) been successfully lifted into a shaft at the Māngere Pump Station site for our Central Interceptor project.
The Central Interceptor is a 14.7kilometre wastewater tunnel that will run underground from Grey Lynn to the Māngere Wastewater Treatment Plant. The $1.2 billion project will drastically reduce wet-weather overflows in Central Auckland waterways, which occur when stormwater floods the system during heavy rain. The project is being delivered by Ghella Abergeldie JV.
Central Interceptor executive programme director Shayne Cunis says lowering the TBM marks an important milestone for the project: “It’s a great day for everyone. We couldn’t have asked for more perfect weather to see Hiwa-i-te-Rangi to be lowered underground. We wish her well as she begins this exciting journey.”
The front shield was carefully hoisted by crane down into the 40m deep launch shaft, which lies below sea level. In coming weeks, the TBM will be assembled underground and undergoing testing.
An official launch ceremony at the end of July will mark the start of digging. As Hiwa-i-te-Rangi cuts through a concrete wall and the journey progresses, gantries will be added to create a long train with an overall length of 190m. Hiwa-i-te-Rangi will head north, and travel under the Manukau Harbour as it travels towards Central Auckland at depths of up to 110m. Lasers will guide the route of the cutterhead, so that the direction is millimetre-accurate.
Two new link sewers will connect with the main tunnel. The first link sewer to be completed will travel from May Rd to Miranda Reserve in Avondale. The second will start near the Mt Albert War Memorial and travel 1.5 kilometres to the Ōrākei sewer main.
TBMs are traditionally given female names and Hiwa-i-te-Rangi was named after a Matarki star. It was chosen by students who attend local schools along the route. Hiwa-i-te-Rangi is one of the stars to which Māori would traditionally send their dreams or aspirations for the new year. She was manufactured in Germany by Herrenknecht AG and arrived in Auckland via ship last year.
An Earth Pressure Balance method of construction is being used. The front of the machine is pressurized to keep groundwater at bay. The TBM is powered by thrust cylinders, which press the cutterhead into the ground. Spoil passes through openings in the cutterhead, along a screw conveyor and conveyor belts, which tip into muck skips. The muck skips are sent down the tunnel by electric locomotive and are removed by crane. Most of the spoil will be deposited at nearby Puketutu Island, where we are carrying out a restoration project on a former quarry. One day the island will be returned to the people of Auckland as a park.
Once completed, the Central Interreceptor will be New Zealand’s longest bored tunnel. Providing both storage and conveyance, it will hold 226,000 cubic metres of water – the equivalent of 90 Olympic-sized swimming pools and act as a buffer for Māngere treatment plant in times of high flow.
Watch the TBM being lowered into the shaft.