In December TBM Florence, which is digging the headrace tunnel on Australia’s Snowy 2.0 project, was transitioning from soft material into harder rock conditions when a depression developed on the surface above the machine. At the time, Snowy Hydro said the integrity of the tunnel had not been compromised, and tunnelling was continuing while work to remediate the surface depression was carried out. A safety exclusion zone was imposed around the surface depression.
Later it said the TBM was paused temporarily while remediation plans were finalised.
In May this year, the New South Wales government imposed conditions on Snowy Hydro before tunnelling could resume.
Now final commissioning tests are under way for the onsite slurry plant that means the dual-mode machine can switch from open excavation to a closed, pressurised mode. This will enable stable excavation and efficient progress through softer ground conditions when required.
Snowy Hydro says a significant testing regime has confirmed grouting and stabilisation of the loose material around TBM Florence has been effective.
Additional stabilisation continues from the surface to solidify loose material above the machine and directly in front of the TBM cutterhead and the rock mass the machine is near.
“We’re carrying out rotations of the cutterhead and minor advances of TBM Florence to ensure the machine is correctly positioned for final commissioning and to confirm the ground support activities are working,” Snowy Hydro says in a statement. “Additionally we are working with NSW departments on environmental approvals for remediation of the surface depression above TBM Florence and to provide assurance that this will not reoccur.”
At the same time, 11m diameter TBM Lady Eileen Hudson has been launched on its second tunnel drive. The TBM was the first to start tunnelling and the first to complete a tunnel when it broke through on the 2.85km main access tunnel at Lobs Hole in October last year.
After being retrieved, the TBM was reassembled with new components. The conveyor stacker, grout batch plant and chiller plant were also relocated from the main access tunnel portal to the Talbingo adit.
TBM Lady Eileen Hudson is 137m long and weights 2,300 tonnes. The 378-tonne cutterhead comprises 70 cutting discs each weighing 290kg.
The TBM will now excavate the 6km tailrace tunnel to connect Talbingo Reservoir to the underground power station complex. Water used to generate 2,000MW of power from Snowy 2.0 will flow out of the tailrace tunnel. Water also enters this tunnel when the power station is pumping..
More than 27,000 concrete segments manufactured at the Polo Flat, Cooma, precast facility will be used to line the tailrace tunnel.
Snowy 2.0 is Australia’s largest renewable energy project. It will link Tantangara Reservoir (top storage) with Talbingo Reservoir (bottom storage) through 27km of tunnels and a power station with pumping capabilities. This will enable water to be released for energy generation at times of peak demand and pumped back to the top storage when there is excess renewable energy in the system, ready to generate again.
