Snowy Hydro has confirmed that construction of Snowy 2.0 continues to make progress across multiple worksites, despite recent challenges at the site which saw the pause of tunnel boring machine (TBM) Florence following the discovery of a surface depression in the ground above the machine.
The company said that at Lobs Hole TBM Lady Eileen Hudson has completed excavation of the 2.7km main access tunnel and TBM Kirsten is almost finished excavating the adjacent 2.9km emergency, cable and ventilation tunnel (ECVT).
At Tantangara, TBM Florence has tunnelled about 150m and is currently located at a depth of approximately 30m below ground. The emergence of the surface depression approximately 9m deep temporarily delayed progress on this particular worksite. The project team is currently conducting works to stabilise encountered soft ground and enable TBM Florence to restart excavating the headrace tunnel.
Importantly, Snowy Hydro stressed, 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 stabilised, prior to striking hard rock, when normal tunnelling is expected 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.
FGJV is currently installing a slurry plant for the TBM that will mean the machine can switch from open excavation to a closed, pressurised mode. This will deliver stable excavation and efficient progress through the softer ground conditions, while enabling the TBM to switch back to open mode when in harder rock.
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.
3D imagery of surface depression above TBM Florence at Tantangara, created using photogrammetry technology
Milestones
A number of milestones have been reached across a range of work fronts on the pumped storage expansion of the Snowy Scheme.
At Lobs Hole, in the main access tunnel, works are continuing on multiple drill and blast cross tunnels. These will link with the ECVT, where TBM Kirsten has tunnelled 2.8km and has reached the site of the underground power station cavern complex. This means Snowy Hydro now has 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.
TBM Lady Eileen Hudson 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, along with the giant surge shaft on the Marica plateau that is already excavated to a depth of more than 20m.
