Meet our TBMs
To dig the main CI tunnel and lay the concrete segments behind it, we’re using state-of-the-art tunnel boring machines or TBMs. Infrastructure constructed by TBMs is strong and reliable, enabling us to excavate through a wide range of ground conditions.
TBMs are traditionally given female names in honour of the patron saint of miners and tunnellers, Saint Barbara. To find a name for our main TBM, we asked children at schools along the tunnel route for ideas. They chose Hiwa-i-te-Rangi, a female Matariki star connected to the promise of a prosperous season. The children thought this name best represented our project’s aspiration to improve the natural environment.
Photo: Hiwa-i-te-Rangi is unveiled to Auckland school children
Hiwa-i-te-Rangi is on her 14.7km journey north from Māngere to Grey Lynn. To bore the tunnel, she uses a massive cutter head - 5.4m in diameter - to grind through a variety of different soils and rocks. This spoil is then transported back to the shaft in skips and lifted out of the tunnel. The spoil is then trucked to Puketutu Island in Māngere to help restore the original volcanic cone. We truck up to 5,000m3
of spoil a week - that's enough to fill up more than 150 six-metre-long sea containers. One day this island will be opened to the public as a regional park.
As she digs the 14.7km tunnel, Hiwa-i-te-Rangi will lay 9,000 precast concrete segment rings - each is made up of six interlocking pieces. The resulting 4.5m-diameter pipe has a durable lining which protects the concrete from corrosion over its 100-year lifespan.
We also have a second TBM, a micro version named Domenica. She is named after members of the contractor’s Ghella family who helped found the company. Domenica is boring two link sewers at depths ranging from 12m to 70m, with a combined length of 4.3km.
Photo: Our micro-TBM Domenica proved popular at her farewell ceremony before she headed underground
Link Sewer C, which runs from May Road in Mt Roskill to Miranda Reserve in Avondale, will have a 2.1m internal diameter. When Domenica finishes that sewer she'll move to our Mt Albert War Memorial Reserve site where she will be widened to 2.4m to bore Link Sewer B.
Domenica builds her tunnels with fully-constructed concrete pipes using a system called pipe jacking. This involves lowering each pipe into the shaft behind the previous one. A hydraulic jacking rig pushes it forward and this gives the TBM her cutting momentum.
Tunnelling work is tough and our crews stay underground for their entire shift as they tunnel 24/7. Give a thought to them as you’re tucked up in bed at night.
Our training TBM honours a pioneering woman of New Zealand education
Around the world, there is a tradition of giving female names to tunnel boring machines. We saw the arrival of our full-size training TBM in 2020 as an opportunity to honour a female New Zealand trailblazer.
Kate Edger was the first woman to gain a University degree in New Zealand. She achieved a Bachelor of Arts in Mathematics, with the degree being awarded on 11 July 1877. The next year, Kate became the founding principal of Nelson College for Girls, and in 1890 she moved to the capital and was active in women’s education and social issues of the day, including the female suffrage movement.
Photo: Kate's family with the official party at the unveiling of the training TBM
To celebrate the training TBM’s arrival, more than 100 local elected members, Watercare directors, industry representatives and project staff joined Auckland’s Mayor and our directors for a dedication ceremony. Special guests of honour were trustees of the Kate Edger Educational Charitable Trust and three generations of Kate’s family - from granddaughter to great, great grandchildren.
The Trust’s lond-standing purpose is to help further higher education for women by providing financial help. Watercare and Ghella Abergeldie JV were pleased to donate $5,000 to enable the Trust to provide assistance to a female engineering student in the Auckland area. In April 2021, the first recipient of the award was Maya Ranzinger who is in her second year of study at Auckland University of Technology.