Waitematā harbour drilling reveals seabed for future crossing plans

NZ Herald

10-05-2025

We've been here before. There was the Skybridge, then the Northern Pathway, and let's not forget mayoral hopeful John Tamihere's double-decker 18-lane proposal.
Yet despite the many plans, reports and debates, no government has managed to get a shovel in the ground.
So, what makes it different this time?
'There's never been any substantive geo-technical drilling in the Waitematā before, so this is really the first time that we're seeing a picture of what the rock conditions are underground,' said Sian France, a geologist and the investigations lead of the Waitematā Harbour Connections Alliance.
Today, the Detail gets a closer look at this jacked-up barge, finding out more about the drilling process, the geological testing and how it's helping further plans for the long-awaited new crossing.
The project should take about seven months, which sounds like a long time, but Mark Ware, project director for NZTA, says there's a lot more to it than drilling a couple of holes.
'Each hole takes between four and five days. So you're drilling upwards of 75 metres in the marine area below the surface and 65 on land,' he says.
Ware is hoping for a decision on the crossing by mid next year.
'Depending on what that decision looks like it will then take us a number of years to finish off the designs, procure our services and contractors, so we're looking to be in the ground or under the seabed by 2029-2030.'
But for this to go ahead, governments over the next couple of parliamentary terms will need to be on board. With an election happening next year and no legislation securing the plan, there is the risk that it could be scrapped in favour of a new idea.
'Hopefully we've got a strong enough case that any government coming in sees the benefit of actually undertaking the work that we're doing and building an alternative harbour crossing,' Ware says.
The drilling is done with a steel pipe that has industrial-grade diamonds on the end of it, which cut through the rock. Sections have to be removed 1.5m at a time.
Then geologists such as Georgia Woodside and Sian France get the extracted material ready for testing.
'Often when it comes out it's got a bit of drilling fluid or a bit of clay from the hole so we wash it off so it's clear what we're looking at and then we box it up, taking great care not to break it because it can be used for different kinds of testing,' Woodside says.
That testing includes looking at the rock formation, and what it's made of.
'For example, here [Waitematā Harbour] we've got the East Coast Bays Formation, so that's saltstone and sandstone interbedded,' Woodside explains.
All of this information is logged and used to inform how the crossing will be built.
'It's all about how the ground will respond to construction activity,' France says.
'So, if you pile for a bridge, if we bring a tunnel boring machine in for a tunnel, how will the ground respond? Will it stay open by itself? Do we need additional engineering means to support it? How do we design and build it in a safe manner?'
France says investigation is important to avoid later cost blowouts, because by the time shovels are in the ground it's too late.
'You've missed the opportunity to really manage cost risk and so that's a really huge part of getting Geotech investigations done upfront.
'We're trying to minimise surprises; there's a whole bunch of really good stats that come out of construction projects in the UK that essentially demonstrate that a very small percentage of overall spending on geotech will significantly reduce the likelihood of having construction overruns.'