Engineers in New South Wales, Australia are working to restart one of the three drilling tunnels on the already delayed Snowy 2.0 pumped storage hydro project after it was halted in December when a 30-ft-deep depression emerged about 100 ft above.

The tunnel boring machine is driving the roughly 10.5-mile headrace tunnel from the high level Tantangara Dam to an underground powerhouse. A second TBM will form the 3. 7-mile tailrace down to the Talbingo reservoir.

According to project owner Snowy Hydro Ltd., the TBM had driven about 500 ft before ground above sank. The machine had been operating in open mode through varying ground conditions from soft, sandy ground to extremely hard rock.

Snowy_Hydro_depression_ENR.jpg3D imagery created using photogrammetry technology shows the depression over the tunnel boring machine.                 Image courtesy of Snowy Hydro


To deal with the soft ground, contractor Future Generation Joint Venture (FGJV) had been injecting grout around the perimeter and reinforced the segmental concrete lining steel ribs. Because of this work, "the integrity of the tunnel ... has not been compromised, and nor has the capacity of the TBM," says the owner.

Before restarting the TBM, the contractor has been probing and grouting up to 50 ft ahead of the face. At the same time, the contractor is setting up slurry plant to allow the machine to function in a closed and pressurized mode while in soft wet soil. The contractor will later stabilize the affected surface and refill the large crater.

Led by Italy's Webuild S.p.A., the joint venture won the $5.4 billion civil and electromechanical contract in the Snowy Mountains four years ago. The team includes Webuild’s U.S. subsidiary Lane Construction and Australia’s Clough Projects Pty., which it recently acquired. 

Of the other two TBMs, one is being prepared to drive the tailrace from the lowe Talbingo reservoir, having completed the roughly 1.7-mile long powerhouse access tunnel four months ago. 

The third machine, which has been driving the 1.8-mile emergency, cable and ventilation tunnel into the powerhouse, will be modified to excavate the pressure shaft, which will slope at up to 25°.

Despite the snags, Snowy Hydro officially forecasts it will starting commissioning the six generators in 2025, with full operation the next year. However, the project is widely reported to be running about a year late. When complete, the 2,000-MW plant will provide 350 GWh of storage.