SHAFTS/KIDSTON PUMPED STORAGE PROJECT | BTS


design takes account of ground, rock wedge and grouting loads plus localised water pressure if any water bearing faults are encountered. Weepholes are placed at 3m maximum staggered spacing. The steel lining was checked for being both empty


with external water pressure, and full with static and transient pressure as well as the shipping and handling loads during placement. The load sharing capability of the rock mass reduces approaching the cavern, and so the thickness of the steel liner ranged from 18.5mm to 26mm depending on the load cases along the penstock. There was also a corrosion allowance included in the thickness calculation. As the water flows out of the powerhouse, having


generated electricity, it exits through a rectangular draft tube which transitions into horseshoe-shaped discharge tunnels. Due to the upward inclination of the tunnels, there


is still a head of water pressure, though not as high as at the intake tunnel but it is still under pressure. The tunnels are inclined upward because the turbines in the powerhouse need to be submerged to prevent cavitation pitting on their steel blades. This arrangement is more notable than with


conventional surface hydroelectric power facilities because of the reversible nature of pumped storage schemes and even more so for Kidston because of the large variation in water levels. Therefore, being under pressure, the area downstream


of the powerhouse cavern at Kidston also has to be steel lined to minimise the hydraulic gradient. The draft tube-to-tailrace transition steel liner (see Figure 4) was designed taking account of the complex change in geometry over a distance of only 10m, where the length was minimised based on the hydraulic gradient requirements. The steel transition structure was modelled in 3D


using STRAND7. The steel plate is 25mm thick with stiffeners and webs and thicker 40mm plate locally for the corner sections. The weight of each transition piece is about 60 tonnes and will have to be transported in


three pieces and welded on site. Mass concrete will then be placed between the liner and excavation. The twin tailrace tunnels are 330m long, on gradients


of 1in 8, inclined upwards from the powerhouse to the lower reservoir at Eldridge Pit. The tunnels pass through the same undifferentiated gneiss rock mass as at the intake tunnel, although the tailrace passes through some faults and the rock mass changes into a weaker breccia towards the Eldridge pit. Less favourable rock parameters are used for this section. The tailrace tunnels will be constructed by drill and


blast methods, with a primary lining and then fibre reinforced cast in-situ concrete for the secondary lining, again with no bar reinforcement. At the time of the presentation the main access tunnel


was under construction, having started in 2022 and was approaching the powerhouse location (see Figure 5). The Wises Pit (upper reservoir) is under preparation,


including the area where the intake shafts will be constructed and the Eldridge Pit (lower reservoir) is being pumped out for construction access. Construction of the Kidston PSH scheme is due to be


completed in 2024 with electricity generation scheduled to start in 2025. In terms of sustainability, the project is re-purposing


existing infrastructure, and hydroelectric energy storage schemes of this nature have a long design life compared to battery storage. The project has a design life of 50 years and is believed to be the first that uses off-river solutions by re-using the same water minimising impacts on the local river system. Using a combination of mixed renewables, the project


will produce enough energy to power 143,000 homes for at least six hours through a single cycling of upper reservoir emptying. Looking ahead, according to the Australia Renewable


Energy Agency (Arena) there are about 20,000 potential sites around Australia that could be adapted in a similar way and if only a fraction of these were converted to PSH then Australia would be well on the way to complete renewable energy.


QUESTIONS AND ANSWERS


Q: Is there any potential for similar systems to combine open pit with underground storage in old mines? A: Theoretically, yes, as all that is required is the head difference and the capability to store water.


Q: How much electricity is required to return the water to the upper reservoir? A: Energy is supplied by other sources but about 20% of the energy generated is required to pump the water back to the upper reservoir. The scheme can also draw on power from elsewhere if there is limited availability of renewable energy.


Q: Were there any environmental risks with the fact that the facility was previously a mine? A: As the system is closed-loop, there should not be any environmental risk outside the facility. The water may be corrosive hence why there is a corrosion allowance in the steel pipes and a durability report was undertaken.


Q: For the weepholes, was there a layer of drainage in the shaft lining? A: The weepholes extended 500mm into the rockmass and then there is a geotextile lining in the weephole.


September 2023


| 13


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33