By Lynda Myer
Due to a surface depression appeared above the tunnel, the TBM remains stalled on the Australian hydro project.
The transferring process of TBM Florence, which is excavating the headrace tunnel at Tantangara, from soft material into harder rock conditions was done in December 2022 and a depression developed on the surface above the machine. While the bored length by this TBM is around 150m and at a depth of 30m, the depression is almost 9m deep.
In order to understanding the ground conditions immediately ahead of the TBM, principal contractor Future Generation Joint Venture (FGJV) is drilling probe holes through the front of the excavation. Additionally, the process of improving any weak zones and limit any water flows is already undergoing by digging 20 grout holes in front of the excavation.
Moreover, in order to allowing the machine to switch from open excavation to a closed, pressurized mode, FGJV is installing a slurry plant for the TBM, while it is due to enable stable excavation through the softer ground conditions and the TBM to switch back to open mode when in harder rock.
According to Snowy 2.0’s statement: “Importantly, 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 project team has paused the machine until about 10-15m of weak material in front of it is stabilized, prior to striking hard rock, when we expect normal tunneling to resume.”
Stage two of the works to stabilize 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.
Snowy Hydro reiterated that, despite the current problems, the project was making progress.
At Lobs Hole, in the main access tunnel, works are continuing on multiple drill and blast cross tunnels. With 2.8 km excavation of the TBM Kirsten and reaching to the site of the underground power station cavern complex, these are going to connect with the emergency, cable and ventilation tunnel. As one of the largest and deepest tunnels in the world, this provides access to the excavation site from both ends of the cavern.
Including altering the levels of the TBM’s tanks and mechanical equipment, TBM Kirsten will soon be modified to dig the inclined pressure shaft on a steep uphill angle, 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, the process of reassembling TBM Lady Eileen Hudson at the Talbingo adit with some new components, including a cutterhead and shields is undergoing. In order to excavating the 6km tailrace tunnel, which will feed into Talbingo Reservoir, it is slated to be commissioned into the mountain later this year.
Excavation of intakes at Talbingo and Tantangara is advancing steadily, along with the giant surge shaft on the Marica plateau that is already excavated to a depth of more than 20m.
Linking Tantangara Reservoir (top storage) with Talbingo Reservoir (bottom storage) through 27km of tunnels and a power station with pumping capabilities, Snowy 2.0 is Australia’s largest renewable energy project, which’s advantages are enabling 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.
