One of the three tunnel-boring machines working on Australia's biggest renewable energy project, Snowy 2.0, is stuck.
Tunnel-Boring Machine (TBM) Florence hit soft ground in Kosciuszko National Park in New South Wales in December and ground to a halt.
The incident caused a hole to appear above the machine, measuring approximately 10 metres across and 4 metres deep.
In December, Snowy Hydro announced it was monitoring a "surface depression" above the TBM.
Cooma local Peter Anderson has long been concerned about the environmental impacts of Snowy 2.0 and decided to go in search of the hole.
"It was a bit like trying to find a needle in a haystack, so I started a fair way out and followed the path of the tunnel," Mr Anderson said.
TBM Florence was commissioned in March last year to drill about 15 kilometres through the mountains. At the time, Snowy Hydro said it could travel 30 to 50 metres a day.
"Technically, [TBM Florence] should be 9 kilometres in but I thought I'd start about 3 kilometres out and start walking my way back in," Mr Anderson said.
"Over four days of searching, searching, searching [for the hole], I finally found it, and where it was, was a great shock to me."
TBM roughly 150m into 15km tunnel
Snowy Hydro did not confirm how far the hole is from the tunnel entrance, but satellite data suggests it is roughly 150 metres from the entrance.
In December, Snowy Hydro said TBM Florence was right underneath the hole.
"In all honesty, when I finally found this cave-in, I was shocked. I just couldn't understand how they could have travelled so little a distance," Mr Anderson said.
In a statement, Snowy Hydro confirmed it had "temporarily paused" TBM Florence while it worked out what to do about the hole.
It says the ground conditions vary there from "soft, sandy ground to extremely hard rock".
Snowy 2.0 is a pumped-hydro project that will pump water through 27 kilometres of tunnels between two dams.
TBM Florence is one of three huge machines that will build those tunnels.
Risks involved in retrieving stuck machine
Snowy Hydro declined 7.30's interview request and did not answer any specific questions about how it plans to remediate the site or when TBM Florence will be back at work.
Professor Simon Bartlett has not worked on Snowy 2.0 but he has been a senior engineer on other pumped-hydro projects in Australia and overseas.
He says retrieving the stuck TBM is not an easy task.
"It'll be a huge jacking task. Because 2,000 tonnes is a lot of weight to lift. About the only other option would be to dismantle it, take it out again and start the tunnel again, which will be a huge delay," he said.
The machine weighs 2,400 tonnes and measures 143 metres in length.
As it bores the tunnel, concrete reinforcements are inserted behind it, meaning the TBM can not be pulled out the way it went into the tunnel.
"It's all good in theory, but these are huge machines and they can get into trouble, particularly if the ground conditions are poor. There's a lot of risks involved," he said.
"I think we're going to see more of what we've seen.
"The concerning thing is that if they've only got 200 metres in 10 months, that's an average rate of only 60 centimetres a day. Now, these machines were designed to travel 30 metres a day, and in good conditions, 50 metres a day."
Watch this story on 7.30 tomorrow night on ABC iview and ABC TV
