Kinchant Dam is a zoned earth and rockfill embankment situated on the north branch of Sandy Creek, approximately 30 km southwest of Mackay in central Queensland. Kinchant Dam was constructed in stages. The ‘Initial Development Stage’ which consisted of an embankment length of approximately 3.3 km and full supply level (FSL) of EL 49.21 m AHD was completed in 1977. Further development completed in 1986 (Stage I) increased the FSL to EL 57.21 m AHD with an embankment length of 5.5 km and a maximum embankment height of 22.3 m. The dam has a storage capacity of 62,800 Ml and a 60 m wide emergency spillway with a fixed crest level of EL 58.21 m AHD, one metre higher than the FSL.
A series of investigations have been carried out since its construction as a consequence of both regulatory safety reviews and observed excessive pore pressures within the foundation that have led to wet patches developing at the toe of the dam. In one area at the toe, pore pressures were such that artesian conditions developed. This paper outlines the history of various stages of construction of the dam, the foundation investigations since construction and the safety review and comprehensive risk assessment process that lead to the upgrade design and construction of remedial works. The remedial works include the extension of the downstream filter material adjacent to the clay core and the provision of additional pressure relief wells at the downstream toe of the dam.
J.P. Giroud, Neil Jacka, Christopher Dann and Jeremy Eldridge
The remediation of a large hydropower canal included the lining of selected reaches of the canal with a geomembrane to extend the life of the canal and enhance seismic resilience. This paper presents a summary of innovative analyses performed to select and design the geomembrane liner system. Two mechanisms that induce tensile stress and strain in the geomembrane following the development of cracks in the supporting subgrade resulting in the deflection of the geomembrane over the cracks under the applied water pressure were analysed. The analysis uses the concept of ‘co-energy’, a geomembrane property that evaluates its ability to withstand stresses and strains together. A range of ballast configurations undertaken to assess the tension, strain and deflection of the geomembrane while evaluating the resistance to hydrodynamic forces and other loads were analysed. Stability analyses showed that geosynthetic reinforcement of the ballast over the upper canal slopes was required.
Keywords: Canal, Lining, Geomembrane, Design, Seismic resilience.
Peter Mulvihill and Ian Walsh
The Falls Dam was constructed in the 1930’s to provide storage for several irrigation schemes in the Manuherikia Valley situated in New Zealand’s South Island region of Central Otago.
The opportunity to retrofit a small hydropower plant to the concrete faced rock fill dam was taken in 2003, utilising existing tunnels complemented by an innovative syphonic penstock system. The key design and construction features of this integrated scheme are described, along with experience from the first 10 years of the generation performance.
Looking ahead, there may be further integration challenges as current investigation of irrigation storage requirements leads to major redevelopment at this dam site and substantial changes to generation parameters.
B. Perrin and J. Vida
The Cotter Dam project represents the most significant infrastructure project in the Australian Capital Territory (ACT) since Parliament House in 1988. Enlarging the Cotter Dam has increased the Cotter reservoir capacity from 3 GL to 78 GL, representing a 35% increase of ACTEW Corporation’s total reservoir capacity for the ACT region and providing water security to facilitate future population growth.
At 87 m high, Cotter Dam is the tallest Roller Compacted Concrete (RCC) dam in Australia. Construction began in October 2009, with excavation of the dam foundation commencing in March 2010. With typically 05H:1V slopes up to 115 m high, excavation posed a number of challenges. RCC placement commenced in August 2011 and continued until December 2012.
Innovation and continuous improvement were crucial to the success of the project. From development of specialised mechanical tools for the abutment excavation, to use of precast, to mechanical paving of the downstream RCC steps, construction practice on Cotter Dam established a number of new benchmarks for RCC dam construction.
This paper will describe the construction innovations used to overcome the challenges associated with construction during foundation preparation and RCC placement for the Cotter Dam Project.
Rob Campbell, Christopher Dann and Mark Foster
Queensland contains some of Australia’s most significant reserves of mineable metallurgical coal, which is an essential raw material used in the production of steel. The area also has large deposits of thermal coal, used for electricity generation.
For the many active open cut and underground coal mines in Queensland, the enduring operational focus is to maximise returns and productivity, while still meeting key safety and environmental responsibilities.
Maintaining open cut pits in a dewatered state is often a key factor in achieving optimal productivity of an open cut mine. In Queensland, for many mines it is not always practical to maintain all pits in a dewatered state, given the subtropical climate and significant rainfall that can occur during the wet season, between the months of November and March. In effectively managing mine water while maintaining production, it is not unusual for excess mine water to be temporarily stored in a designated open cut pit.
The typical scale and arrangement of open cut pits at mine sites in Queensland is such that relatively deep and high volume pits can be separated by relatively narrow “landbridges”, consisting of in-situ material or mine spoil. The situation can therefore arise where a significant volume and head of mine water is stored in one pit, with mining operations continuing in an adjacent pit, and the landbridge is required to perform as a water retaining structure. This is a scenario that might not have been considered when the landbridge was originally constructed. This paper presents a study of two such landbridges at either end of a mine pit in Queensland, over a 5 year period from 2008 to 2013, with mining activities in the pit ranging from dragline pre-stripping to open cut mining, to large scale construction works and underground mining. By employing a long term interactive approach with mine operations personnel and utilising quantitative risk management techniques, risks were effectively managed, helping the mine to maintain operations while meeting safety and environmental requirements.
Jeong Yeul, Lim
For various historical reasons and some technical reasons, the safety of dams has been evaluated using an engineering standards-based approach, which was developed over many years. It was used initially for the design of new dams, but increasingly has been applied over the past few decades to assess the safety of existing dams. Some countries have carried out risk assessments of existing dams that included both the structural and hydraulic safety of the dam and social risk. These methods developed by other countries could be adapted to assist in decision-making for dam safety management. Unfortunately, methods for risk assessment of dams were not established in Korea. This study outlines a beginning risk analysis for structural safety management. The first stage consisted of research on the present domestic dam safety guidelines and reviewing operations for management systems of dam safety abroad. Also, dam risk analysis requires reliable data on dam failure, past construction history and management records of existing dams. A suitable risk analysis method of dams for structural safety management in Korea is use of event tree, fault tree and conditioning indexes methods. A pilot risk assessment was carried out for two dams. The dam risk assessment process was thus established, and we learned the importance of risk assessment. The future includes additional research and risk analysis to develop the system.