14 Feb, 2023 By Ella Jessel
Australia’s largest renewables project Snowy Hydro 2.0 has hit another setback after a huge sinkhole opened up in one of its main drilling tunnels
One of the £3.3bn (A$5.9bn) project’s three tunnel-boring machines (TBM) near Tantangara dam in New South Wales has been “temporarily paused” while engineers work out how to proceed.
In December, Snowy Hydro reported a “surface depression” after the 11m Herrenknecht-designed TBM machine, dubbed Florence, hit soft ground just a short distance from the tunnel entrance.
At the time, the Commonwealth-owned power giant said drilling was ongoing, yet it has now confirmed TBM Florence had now been “temporarily paused” while engineers finalise plans to fix the hole.
It’s the latest blow for the giant hydro project, which has already suffered from rising costs and lengthy delays. It involves complex engineering, including linking two existing dams by tunnels up to 27km in length, and building an underground power station.
In the Australian Senate on Monday, new Snowy Hydro chief executive Dennis Barnes told senators it was too early to say whether the issues at Tantangara would cause further delays. He said the main contract cost had not shifted from £3.3bn ($5.9bn).
Snowy Hydro chief operating officer Roger Whitby confirmed media reports of a large sinkhole in the ground surface, adding it was around 50m to 70m deep.
“We are working through that carefully so that the tunnel boring doesn’t become bogged,” he said.
Senator Malcolm Roberts replied: “Wow. Having come from the mining sector that would seem pretty severe at that depth.”
Bill Grose, a civil engineer and independent tunnelling consultant, said a sinkhole was “unusual but not unheard of”, adding ground conditions were one of the main challenges on a complex project like Snowy Hydro 2.0.
He said: “I expect that the project team and TBM designers and manufacturers are well aware of the risks, and will have procedures to deal with them as and when they arise.  This TBM has a long way to go, in harder ground and deeper terrain.”
Grose added that from the information issued by Snowy so far, it was not clear if TMB Florence was stuck or had been stopped while work is carried out to stabilise the sink hole.
He said: “TBMs are powerful machines and this one is designed to deal with hard rock, so I would expect the sinkhole to be remediated and the TBM to continue, unless there is something significant missing from the reports to date.”
Announced by former prime minister Malcolm Turnbull in 2017, Snowy Hydro 2.0 is an expansion of the Snowy Mountains Hydroelectric Scheme, which was commissioned in 1974.
The project, which will also include an underground power station, will see water pumped to the upper dam when there is surplus renewable energy production and the demand for energy is low, and then released back to the lower dam to generate energy when electricity demand is high.
The hydro will provide around 350,000 megawatt hours of large-scale storage to the National Electricity Market, enough to power 3M homes over the course of a week.
Late last year Snowy Hydro’s completion was pushed back 12 months to the end of 2027.
A Snowy Hydro spokesperson said: “Snowy Hydro and the Snowy 2.0 EPC contractor, Future Generation Joint Venture, are focused on delivering the project safely and in a manner respectful of the sensitive environment, while managing impacts caused by external events including Covid-19, high material costs, global supply chain constraints, labour shortages across the Australian construction industry and ongoing weather conditions.”
It added that At Lobs Hole, the main access tunnel excavation by TBM Lady Eileen Hudson is completed and the emergency, cable and ventilation tunnel excavation by TBM Kirsten is close to completion.
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