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Peter Buchanan, Malcolm Barker, Paul Maisano, Marius Jonker
Kangaroo Creek Dam located on the Torrens River, approximately 22 km north east of Adelaide, is currently undergoing a major upgrade to address a number of deficiencies, including increasing flood capacity and reducing its vulnerability to major seismic loading.
Originally constructed in the 1960s and raised in 1983, recent reviews have indicated that the dam does not meet modern standards for an extreme consequence category dam.
The original dam was generally constructed from the rock won from the spillway excavation. This rock was quite variable in quality and strength and contained significant portions of low strength schist, which broke down when compacted by the rollers. The nature of this material in places is very fine with characteristics more akin to soil than rock. Review of this material suggests that large seepage flows (say following a major seismic event and rupture of the upstream face slab) could lead to extensive migration of the finer material and possible failure of the embankment. However, it is also envisaged that the zones of coarser material could behave as a rockfill and therefore transmit large seepage flows, which may result in unravelling of the downstream face leading to instability.
This paper addresses the design of the embankment raising and stabilising providing suitable protection against both these possible failure scenarios, which tend to lead to competing solutions. The final solution required the embankment to be considered both as a CFRD and a zoned earth and rockfill embankment.
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2016 Papers
2016 – Kangaroo Creek Dam Embankment Raising and Stabilisation – Balancing Competing Objectives
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Peter Buchanan, Malcolm Barker, Paul Maisano, Marius Jonker
Kangaroo Creek Dam located on the Torrens River, approximately 22 km north east of Adelaide, is currently undergoing a major upgrade to address a number of deficiencies, including increasing flood capacity and reducing its vulnerability to major seismic loading.
Originally constructed in the 1960s and raised in 1983, recent reviews have indicated that the dam does not meet modern standards for an extreme consequence category dam.
The original dam was generally constructed from the rock won from the spillway excavation. This rock was quite variable in quality and strength and contained significant portions of low strength schist, which broke down when compacted by the rollers. The nature of this material in places is very fine with characteristics more akin to soil than rock. Review of this material suggests that large seepage flows (say following a major seismic event and rupture of the upstream face slab) could lead to extensive migration of the finer material and possible failure of the embankment. However, it is also envisaged that the zones of coarser material could behave as a rockfill and therefore transmit large seepage flows, which may result in unravelling of the downstream face leading to instability.
This paper addresses the design of the embankment raising and stabilising providing suitable protection against both these possible failure scenarios, which tend to lead to competing solutions. The final solution required the embankment to be considered both as a CFRD and a zoned earth and rockfill embankment.
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2021 Papers
2021 – Analysis of an embankment dam on permeable rock foundations
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Jonathon Reid, Brendan Trebilco
The dam reviewed was designed and constructed in two stages, with the embankment completed in 1965. The dam comprises a 37 m high earth and rockfill maximum section on the creek alignment and zoned earthfill embankments of varying arrangements on the abutment flanks with a total crest length over 2km.
A Dam Safety Review was undertaken as part of the owners on-going commitment to maintain its portfolio of dams in a safe and functional state. The dam has suffered from high seepage rates that were first observed in 1971 after the reservoir rose to a historic high level, which was then exacerbated in 2011 after the reservoir rose a further 10m to reach the Full Supply Level for the first time. Reviews of the embankment stability at this time resulted in operating restrictions being placed on the reservoir level.
Detailed instrumentation data collected over a range of filling events showed the rock foundations to be highly responsive in the areas of observed seepage. This resulted in rapid pore pressure responses in foundation soils and the lower portion of the embankment after a rise in reservoir level, but a much slower pore pressure response in the upper parts of the embankment.
Seepage and stability analyses were undertaken based on the high quality instrumentation data to review the stability of the sections for various operating levels and with projected pore pressure increases for rapid flood loading scenarios. The paper explores the sensitivity of the analyses completed and how different construction standards applied to varying sections on the same embankment resulting in acceptable and undesirable outcomes.
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