INTERNATIONAL | SHAFT TUNNELING
DIGGING DEEP AT KIDSTON
Various lessons have been unearthed during excavation of the underground shafts at the Kidston pumped storage project in Australia
The 250MW Kidston pumped storage project is currently under construction and will be the first pumped hydro project in Australia for over 40 years. It will also be the first to be developed by the private sector and the third largest electricity storage device in the country. Forming part of the Kidston Clean Energy Hub in North
Queensland, it also comprises a solar and wind power project. Genex Power, the company which owns the project,
recently discussed the lessons it has learnt with respect to the excavation of the project’s shafts. Four shafts are required to be excavated:
● Ventilation Shaft – 4.1m (13.5ft)-diameter (excavated), 243m (266yd) deep.
● Cable Shaft – 4.1m-diameter (excavated); 252m deep. ● Intake Shafts x 2 – 5m-diameter (excavated); 244m deep.
Raisebore techniques were used to sink the shafts, with the shafts excavated from the bottom up. This was made possible due to the availability of underground caverns prior to excavation commencing. The general methodology followed was: ● Establishment and survey. ● Installation of pilot hole. ● Attachment of cutterhead and ream the shaft towards the surface.
● Removal of cutterhead and dis-establishment.
Genex discussed various key challenges and lessons learned relating to the raisebore operations and focused on ground conditions, the pilot hole, and reamer operations and removal.
GROUND CONDITIONS During raisebore operations, the excavated shaft is an unsupported circular profile, and support can only be given once the reaming operations are complete. Raisebore shaft construction techniques are normally adopted where ground conditions are favourable, access is provided to the shaft bottom, and the project shaft diameter and length are deemed as being suitable for the equipment available. Where the ground conditions are less stable and at risk of collapse/ ravelling, then structural ground support treatment is required. Following a comprehensive geotechnical
investigation, Genex identified that all four shafts would encounter competent rock, with the exception of the top 20m of ground for the ventilation and cable shaft locations where extremely weathered rock was found. This could result in potential ground squeeze, ravelling and stability issues if left unsupported. As such, the project commenced the installation
of a secant piled ring in the upper zone of both the ventilation and cable shafts as an advanced pre-sink activity to the raisebore operations. This activity was not included as part of the original scope of works as
Above left: Underground construction starts Above right: Tunneling works pictured in February 2022 50 | Spring 2025
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