Second tunnel excavated for Snowy 2.0

The 2.93km emergency, cable and ventilation tunnel (ECVT) has been excavated and fully lined with 13,140 concrete segments by TBM Kirsten. It follows the excavation of the adjacent main access tunnel (MAT), which was completed in October 2022.

Snowy Hydro CEO Dennis Barnes said Snowy 2.0 was continuing to make solid progress, with around 6km of tunnelling by TBMs completed, and drill and blast excavation of the power station cavern about to start.

“We are extremely pleased the ECVT excavation has been completed and the whole project team is excited to be moving into the next critical phase of construction. Our huge power station cavern will be located about 800m underground and will be one of the largest and deepest in the world.

“We are also using drill and blast methods to construct cross passages linking the ECVT with the MAT,” he said.

TBM Kirsten is now being modified to excavate the inclined pressure shaft and line it with concrete segments.

“The shaft is 1.45km long and excavating a segment-lined tunnel of this length at a very steep 47% incline using an 11m diameter TBM is without precedent internationally,” said Barnes. 

Modifications to Kirsten include altering the levels of the TBM’s tanks and mechanical equipment so they remain horizontal when travelling up the incline, and converting the walkways into steps and ladderways. 

Also being installed is a screw conveyor to extract excavated rock from the cutterhead to a sandwich conveyor system with face-to-face rubber belts that help constrain the crushed rock so it can be transported down the slope without spillage.

Additional plant and equipment will also be installed in the ECVT tunnel to support the excavation activities including: an overhead crane, a conveyor transfer station, monorail manrider for personnel access, and rack and pinion mechanism for plant access to the TBM. 

There is currently a project workforce of more than 2,700 across four major worksites building Snowy 2.0.

The project is not without its problems, however. Earlier this month it was announced completion could be delayed by up to two years, which Barnes said was the result of four factors: the soft ground that halted tunnelling at Tantangara; some technically complex design elements requiring more time to complete, making the final design now more expensive to construct; the Covid-19 pandemic; and the effect of global supply chain disruption and inflation impacting the cost and availability of a skilled workforce, materials, and shipping. 

In December last year, TBM Florence stopped work on the headrace tunnel at Tantangara after a surface depression developed above the machine. The TBM was transitioning from soft material into harder rock at the time. The New South Wales government has said tunnelling cannot resume until Snowy Hydro has demonstrated the project can proceed without further environmental damage.