TBM - Key Facts
City Rail Link’s Tunnel Boring Machine (TBM), Dame Whina Cooper excavated two 1.6-kilometre-long tunnels from Mt Eden to central Auckland
The TBM completed its first excavation just before Christmas 2021 and was then dismantled and returned to Maungawhau /and reassembled to excavate the second tunnel
• The two CRL tunnels are parallel and run underneath some of the city’s most iconic areas, such as Grafton, the central motorway junction, Karangahape Road and the city centre.
• The TBM worked 24/7, operated by a crew of 12 underground and a team of 12 above ground
• The TBM multi-tasked underground: excavating the tunnels, removing dirt and rocks to the surface, and installing precast concrete panels that line the tunnel walls
• At peak operation, the TBM travelled 32 metres a day
• The machine’s diameter is 7.15 metres (an adult giraffe is about six metres tall), weighs 910 tonnes (that’s roughly the combined weight of nine blue whales, the largest animal ever known to have existed), and the total length is 130 metres (a rugby field is up to 120 metres)
• The TBM was custom built for central Auckland soil conditions by the German tunnel machine company, Herrenknecht, for the Link Alliance – the group of New Zealand and international companies responsible for the main CRL contract
• To honour St Barbara, the patron saint of miners, machines working underground are traditionally named after women of significance and mana – New Zealanders helped CRL chose the name that honours Dame Whina Cooper, the Māori rights champion
• A Te Waihorotiu Station (Aotea) team member gifted a hard hat painted with Dame Whina Cooper’s image to the TBM crew. The hard hat symbolises the commitment to protecting people’s health, safety and wellbeing, and the connection between each of the project’s main construction areas –
• While the TBM was underground, people above it felt little to no impacts. This is because it is an Earth Pressure Balanced TBM – it controls and balances the pressure of the earth it excavates which stabilises the tunnel face and reduces the possibility of settlement occurring.
Learn more about our big machine
Commonly asked questions
TBM looks huge. How long was it? 130 metres (a rugby field is up to 120 metres long).
Who built it? A German tunnel machine company, Herrenknecht, at their Chinese factory.
Is it the same TBM that was used for the Waterview tunnel? No but the TBM for the Waterview Tunnel was also built by the same company at the Chinese factory. TBMs are built for specific jobs.
How much did the TBM cost? $13.5 million.
How fast did it travel? TBM can travel 32 metres a day.
What about the spoil? Where did it go? Up to 1,500 tonnes of spoil was excavated each day. Spoil from Mt Eden was a mix of cleanfill, managed and contaminated. The spoil was either wet spoil extracted by the TBM or a clean, dry type of spoil removed during initial tunnelling operations.
Cleanfill was disposed of at the Three Kings Quarry in Mt Eden. All other spoil – managed or contaminated – was trucked to various disposal sites at Mercer in Waikato.
Did the TBM also line the tunnel walls? Yes, besides excavating the tunnels and removing dirt and rocks to the surface, it installed precast concrete panels that will line the tunnel walls.
How many people were in the TBM? Up to 12 people.
At one stage, it’s went under the southern motorway. If you’re on the motorway did you feel it? No. This is because it is what is called an Earth Pressure Balanced TBM. This means it controls and balances the pressure of the earth it excavates which stabilises the tunnel face and reduces any possibility of settlement occurring.
What happened after the second tunnel was built? The TBM was dismantled and moved in pieces to the Ports of Auckland and transported back to its German manufacturer called Herrenknecht.
The machine had arrived in kitset pieces from that company’s factory China in late 2020.
The company deconstruct the machine and re-use suitable parts on multiple TBMs in the future. Every TBM has a full circle lifecycle. But our job isn’t done We need to put in the infrastructure such as tracks and signals ready for the trains.
What hours did it work? 24/7.
Who chose the name? Dame Whina Cooper was chosen after a nationwide competition for a name of a ground-breaking woman. Dame Whina at the age of 80, led a land march from Northland to parliament and devoted her life to fighting discrimination.
Why call the TBM something? Traditionally, TBMs are given female names in honour of Saint Barbara, the patron saint of miners and those who work underground. This tradition is said to bring good luck to the work ahead.
What sort of rock did it encounter? The ground conditions for the TBM alignment is East Coast Bays Formation rock of the Waitematā group https://en.wikipedia.org/wiki/Geology_of_the_Auckland_Region
