Snowy 2.0 prepares to tunnel inclined pressure shaft

The steep shaft, which has a 47% incline, forms part of the waterway and will connect the headrace tunnel with the underground power station. It is 1.6km long and has a 10m diameter.

After finishing the 2.9km emergency cable and ventilation tunnel, TBM Kirsten has been substantially modified to tunnel uphill to excavate the IPS.

The Herrenknecht machine’s working platforms, equipment and operator’s cabins all pivot to remain horizontal and the walkways become steps and ladderways. 

A screw conveyor will move excavated rock from the cutterhead. This feeds into a sandwich conveyor that has face-to-face rubber belts to hold the material so it can be transported down the steep slope without spillage.

At the project’s precast manufacturing facility in Cooma, one of the two carousels has also been modified to produce the precast segments for the IPS.

The IPS segments involve a world-first force-activated coupling system designed to withstand the powerful internal forces of water moving through the inclined tunnel.

Project director Dave Evans believes the specially manufactured segments will change the world of hydropower.

“It means we can do less steel lining, we can move power stations closer to the surface which is what we’ve done here, and construct an inclined pressure shaft with a TBM which all makes it safer, quicker and the quality a lot better,” he said.

To cope with the extreme and fluctuating water pressures in the IPS, the concrete segment rings lining the tunnel require bespoke connectors. The force activated coupling system (FACS) comprises specially-developed steel couplers with pin and socket elements.

When the segment rings are interlocked, the pre-stressed FACS keep the joint closed when the tunnel experiences sharp changes in pressure from turbine operations and shutdowns.

The new technology has been developed by Future Generation JV partner Webuild and designer Lombardi.

A large-scale test is being conducted by installing eight FACS rings to link the emergency, cable and ventilation tunnel with the IPS.

In January, Snowy Hydro announced the breakthrough of the final three metres of the power station’s 223m-long transformer hall cavern crown.

Snowy 2.0 is Australia’s largest renewable energy project. It will link Tantangara Reservoir (top storage) with Talbingo Reservoir (bottom) through 27km of tunnels and a power station with pumping capabilities. The hydropower station will be located approximately 800m underground at Lobs Hole in the Snowy Mountains in New South Wales.