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Long-distance microtunnelling projects exemplified in New Zealand

Wellington harbour - New Zealand

New Zealand is responding to projected population growth and upgrading ageing wastewater pipes in the country’s major trenchless works for the last year.

Central interceptor project marches on
In November 2021 Watercare okayed a design change that removed the need for one of the projected construction shafts on the Central Interceptor project, significantly decreasing the project’s impact on the local community.

The adapted plan involved a longer, slightly curved tunnel. Executive program director Shayne Cunis said that, at 1193 m, the new tunnel would be the longest micro tunnel boring machine (mTBM) drive in New Zealand.

The Central Interceptor project aims to drastically reduce wet-weather overflows, and keep up with the rapidly growing population of Auckland.

The primary tunnel boring maching (TBM), Hiwa-i-te-Rangi has been responsible for digging a 14.7 km long tunnel from the Māngere Wastewater Treatment Plant to Grey Lynn. It was delayed by the COVID Omicron variant for nine days – 26 February until 6 March – after which only limited tunnelling was allowed due to restrictions.

The mTBM Domenica reached a massive milestone in December last year when it broke through at the Haycock Avenue shaft in Mt Roskill, despite COVID lockdowns causing delays that risked Domenica becoming stuck if it remained stationary for too long.

The mTBM completed its second, shorter drive at the end of June 2022, connecting a 2.1 m sewer pipe to the main Central Interceptor wastewater tunnel.

The Central Interceptor project is expected to be completed in 2026 and will store and transport stormwater and wastewater to the Māngere Wasterwater Treatment Plant.

Takapuna benefits $5.4 million wastewater pipe upgrade
In May 2022 work started with on relining the wastewater pipe that runs the full length of Takapuna Beach. 

The pipe is over 60 years old and was identified as being in desperate need of an upgrade in order to reduce overflows and improve the quality of water at the beach.

Trenchless technology was used to line the pipes with PVC, making the project faster and reducing the impact on the community. The work included the assessment of 36 manholes and the necessary repair work.

Barber Grove to Seaview Wastewater Treatment Plant Pipe Duplication
The end of 2021 saw the microtunnelling contract awarded for the Barber Grove to Seaview Wastewater Treatment Plant Pipe Duplication project in the Lower Hutt region in Wellington.

Wellington Water, on behalf of the Hutt and Upper Hutt City Councils, worked on duplicating the existing water main by installing a new 1.2 km long, 1 m diameter rising main from the Barber Grove Pump Station to the Seaview plant.

At more than 50 years old the existing pipe represented a higher risk of wastewater entering the Te Awa Kairangi and Waiwhetu stream in the case of an earthquake and conveyed 90 per cent of the wastewater from the Hutt Valley’s residents.

Wellington Water worked with partner Stantec and awarded the tunnelling contract to McConnell Dowell. 55 per cent of the project involved trenchless technologies.

On 5 August Wellington Water announced that the project’s mTBM, named Te Rū Tiokaoka, was in the ground for the journey along Randwick Road to the Seaview Roundabout. The project aims to be completed in early 2023.

Warkworth-Snells wastewater pipeline
In July of this year, Watercare announced that it had received the green light for the construction of a new wastewater pipeline from the Lucy Moore Memorial Park Pump Station in Warkworth to the new Snells-Algies Wastewater Treatment Plant.

The 5 km pipe is a critical element that makes up part of a more than $300 million investment program for the north-east region.

The pump station was in the process of being built, and the new treatment plant at Snells Beach under construction. As well as supporting the growing population in the area, connecting the pump station with the treatment plant will help to clean up the Mahurangi River, which currently receives discharge from the existing Warkworth Treatment Plant.

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This article appeared in the October edition of Trenchless Australasia. Access the digital copy of the magazine here.

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