“TBM Florence remains fully operational and is now more than 800m into excavation of the Snowy 2.0 headrace tunnel at Tantangara. The TBM has operated successfully since its restart on 8 December 2023 and has moved through identified soft ground into hard rock,” the company said in its latest project update.
The three TBMs working on the project have tunnelled a total of approximately 9km.
`’As provided in evidence at two recent Senate Estimates hearings, Snowy Hydro has been investigating options to de-risk the headrace tunnel construction by excavating from the other end. This work remains ongoing,” Snowy Hydro said.
TBM Florence restarted in December 2023, a year after it was halted when a surface depression appeared above the machine.
Also in the latest update, Snowy Hydro said a surge shaft at Marica was now under construction.
The surge shaft has two key roles in the operation of a hydro power station: as a water storage and vacuum relief when the power station starts up, and to absorb the momentum of water movement within the headrace when the power station is shut down.
The Marica surge shaft is about 28m in diameter and is currently more than 80m deep.
During construction, the walls of the shaft are supported temporarily by rock bolts and shotcrete and once it is excavated to its full depth of 250m, a permanent concrete lining will be installed from the bottom up.
“We are excavating the shaft with a number of excavation methods, including using 36-tonne excavators that place loads of material into kibbles,” the update says.
An integrated work platform and personnel hoist is in the final stages of commissioning to provide worker access now the shaft is becoming very deep.
Snowy 2.0 project manager Richard Clarke said building in steep terrain was challenging and required specialised rope access workers to install ground support for safety and stability.
Marica Trail provides all-weather access to the surge shaft site but it too was challenging. The 6.5km-long road climbs 320m and has multiple water crossings.
At Tantangara, drill and blast excavation to join the intake and gate shaft is underway from both structures. The transition from the intake changes shape as it is excavated to become the connection tunnel to the gate shaft.
At the same time, crews have started drilling and blasting from the gate shaft to merge into the headrace tunnel alignment excavated by TBM Florence.
When completed, water will enter the headrace tunnel from the intake, on its way to the power station.
The target date for commercial operation of all units is December 2028, with first power expected in the second half of 2027.
