Construction of Snowy 2.0 - a critically important, pumped-hydro expansion of the Snowy Scheme in Australia, continues to make progress across multiple worksites. The project involves linking two existing dams, Tantangara and Talbingo, through 27km of tunnels and building a new underground power station.
At Tantangara, the project team is currently conducting works to stabilise encountered soft ground and enable TBM Florence to restart excavating the headrace tunnel.
TBM Florence has tunnelled about 150 m and is currently located at a depth of approximately 30 m below ground. A surface depression recently emerged in the ground above TBM Florence, which has temporarily delayed progress on this particular worksite. The depression is approximately 9 m deep and continues to be monitored.
The integrity of the tunnel, which is supported by a concrete lining and steel ribs, has not been compromised, and nor has the capacity of the TBM. The machine has been paused until about 10-15m of weak material in front of it is stabilised, prior to striking hard rock, when the team expects normal tunnelling to resume.
Snowy 2.0 principal contractor Future Generation Joint Venture (FGJV) is drilling probe holes through the front of the excavation to understand the ground conditions immediately ahead of the TBM. Grout is injected in front of the excavation to improve any weak zones and limit any water flows. Grouting is well underway from TBM Florence, with 20 grout holes drilled to date in the current location.
Stage two of the works to stabilise the ground in front and above the machine will involve ground improvement from the surface. Once the area is grouted, the depression will be backfilled and revegetated.
At Tantangara FGJV is currently installing a slurry plant: civil and concrete works are almost complete and the contractor is well on its way with the assembly of a separation plant, bentonite mixing silos and water tanks. Electricians are busy installing motors, completing internal wiring and running high voltage cables to the substations. The plant will enable TBM Florence to switch in the headrace tunnel from open excavation when in harder rock to a closed, pressurized mode for efficient progress in the softer ground conditions.
At Lobs Hole, in the main access tunnel, works are continuing on multiple drill and blast cross tunnels. These will link with the 2.9km emergency, cable and ventilation tunnel (ECVT), where TBM Kirsten has tunnelled 2.8km and has reached the site of the underground power station cavern complex. This is a great milestone for Snowy Hydro as the team now have access to the excavation site from both ends of the cavern, which will be one of the largest and deepest in the world.
TBM Kirsten will soon be modified to excavate the inclined pressure shaft on a steep uphill angle. Modifications include altering the levels of the TBM’s tanks and mechanical equipment so they are level when travelling up the 25-degree incline, and converting the walkways on the machine’s sides into steps and ladderways.
Meanwhile TBM Lady Eileen Hudson - completed the excavation of the 2.7km main access tunnel and is being reassembled at the Talbingo adit with some new components including a cutterhead and shields. It will be launched into the mountain later this year to excavate the 6km tailrace tunnel, which will feed into Talbingo Reservoir.
Excavation of intakes at Talbingo and Tantangara is advancing steadily. The Tantangara intake stage 1 on the Marica plateau is already about 20 m. Stage 2 works will extend the excavation a further 30 m, so about 50 m depth in total. Once these works are complete, a concrete diffuser structure will be built at the base of the excavation. The final step will be to remove the temporary rock plug and allow the reservoir water to enter the intake and headrace tunnel.
For further information click here for a video also here and au/38 for further information in the tunnelbuilder archive Visit https://www.snowyhydro.com.au/ . 15/23.
