Our tunnel boring machine,
named after New Zealand’s iconic Dame Whina Cooper,
will help construct the City Rail Link's twin tunnels
beneath Central Auckland.
The TBM’s underground journey begins at Mt Eden
where it moves forward to Karangahape and then to Aotea.
It's a 1.6km journey that the TBM will undertake twice.
Expert TBM manufacturers Herrenknecht designed and built the TBM,
taking into account the complex challenges the machine has ahead of it.
Challenges include the material the machine will excavate,
called East Coast Bays Formation,
the 340 metre curve in its drive
and the steep slope it will navigate.
After launching from Mt Eden,
the TBM will plunge at a steep slope of 3.5%
to pass underneath ‘Spaghetti Junction’.
There are many different types of tunnel boring machines.
To help with these challenges,
and to ensure people above ground don’t notice it working below,
the Dame Whina Cooper TBM is an Earth Pressure Balance machine.
It’s 7.15 metres in diameter, which makes it taller than a giraffe,
and is 130 metres long, that's 10 metres longer than a rugby field!
The rotating cutterhead breaks and removes materials in front of the machine.
As it cuts away the ground material, concrete lining segments
are installed to create the new walls of the tunnel.
The machine uses hydraulic cylinders to push itself forward off the newly placed segments.
Although the machine’s top speed is 32 metres a day,
we expect it will move forward 15 metres a day on average.
That's impressive for something that weighs 910 tonnes.
The Machine is a moving, underground factory
and although it has lots of digital programming to move it forward,
we need 12 people on it below ground and another 12 people supporting it above ground 24-7.
Inside the shield is a ‘pilot cabin'. This is the machine’s control room.
Motors turn the cutterhead and are located near the screw conveyor.
This controls how fast the material excavated by the cutterhead is removed.
It also keeps the pressure at the cutterhead stable
which ensures you or I don’t notice it working as we go about our days.
It also houses an air lock,
which workers pass through before they enter and exit the excavation area
so that they can acclimatise to the pressure.
The excavated material is moved from the screw conveyor
onto a conveyor belt.
The tunnel lining is made up of hundreds of concrete rings.
One ring is formed by seven concrete lining segments.
These segments are transported to the TBM by a multi-service-vehicle.
You can see that in yellow.
They’re lifted from the multi-service-vehicle onto the segment feeder
where they wait to be placed into their permanent position.
Once all seven are in place, the TBM moves forward.
To make the TBM a comfortable place to work for its underground crew,
toilets and a small lunch room are on board.
Protecting their safety is the most important thing
so all of our crew will have equipment on them to use in case of an emergency,
as well as the refuge chamber that will further protect them.
The TBM pilot watches everything happening from the control room
and can stop everything at the push of a button!
The Dame Whina Cooper tunnel boring machine is working hard
to help build the City Rail Link which will
unlock Auckland’s public transport network.
The machine’s journey will finish in 2022
and the City Rail Link is due to be complete in late 2024.