The Stage I construction of the Ross River Dam was completed in December 1973. The reservoir
reached full supply level (FSL) and then spilled in January 1974. In 1976, the left embankment was
raised to Stage II level. Spillway gates were installed in February 1978 with full supply level for
Stage 1A (FSL).
In the years following the first filling of the reservoir after the raising of FSL, salt scalding
downstream of the northern portion of the left embankment occurred. This was attributed to
foundation seepage. Investigations started in 1978 to define what remedial measures were required to ensure the safety of the left embankment. Fissured clays were first discovered in the foundations of the Ross River Dam during these investigations.
Fissures could substantially reduce the overall strength of the soil foundations. Therefore the effect of these fissures needs to be considered when evaluating the acceptable levels of reliability against embankment failure. More extensive fissuring was discovered during the current investigations and a cataloguing system was employed to characterise the foundation conditions.
A simplified layer model was adopted early on in the design but did not fully demonstrate the
complexity of the subsurface conditions. Extensive use was made of historical geological data,
current investigation data and the application of GIS systems. The resulting model more clearly
represents the foundation conditions and high degree of variability and was used in subsequent risk assessments for the upgrade design.
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Now showing 1-12 of 64 2969:
Trevor Allen, Phil R. Cummins, Trevor Dhu, John Schneider
Ground-motion attenuation models have been derived for the Australian crust. These models
employ both empirical and stochastic methods and are the first spectral ground-motion models to be
based entirely on Australian ground-motion data. In the past, these studies have been hampered by a lack of quality ground-motion data given Australia’s relatively low levels of seismicity.
Two key datasets have been employed to derive empirical ground-motion attenuation models for
Australia; one from data recorded in the Palaeozoic crust of southeastern Australia (SEA) and the
other from the Archean shield region of southwestern Western Australia (WA). Empirical ground motion models are derived for each of these datasets. In general, long-period (e.g. 1 sec) ground motion energy appears to attenuate less in WA than in SEA. These empirical models suggest that SEA has similar near-source attenuation with eastern North America. Because of the limited and spatially clustered nature of the WA dataset, however, we could not constrain attenuation models as well as in SEA.
Stochastic methods are employed to simulate ground-motions for larger earthquakes in regions
where recordings from real events are not available. These models are largely based upon source and attenuation parameters derived from empirical studies. Stochastic models are derived for SEA only.
Spectral ground-motion predicted by these models are generally lower than ground-motion predicted
by both eastern and western North American models, particularly at short-periods (T < 0.5 sec).
Results from this study have significant implications for earthquake hazard and risk in Australia. They
suggest that we are currently overestimating earthquake hazard in SEA. Furthermore, they suggest
that we cannot simply rely on North American ground-motion models to predict earthquake ground
motions in Australia.
N. Vitharana and S. Terzaghi
There is a large stock of embankment dams throughout the world needing the assessment of their
safety as required by modern dam safety regulations. Due mainly to economic and site constraints
associated with potential dam upgrading work, it is imperative that a rational approach be adopted in
assessing their safety and in designing the remedial works. One of the most important criteria is the
selection of appropriate geotechnical parameters under different conditions. Predominant loading
conditions in a dam are much different from those in other structures such as bridge and building
foundations and therefore the direct adoption of traditional approaches may not always be valid. This
paper presents the various aspects of issues associated with the stability assessment of dams including
the rational selection of the parameters and numerical codes available to dan/geotechnical engineers
to assess their safety.
Howard and Opper
Dam safety planning is a team game. There are many players involved and there is a need for information to be shared and actions to be properly coordinated. The State Emergency Service is the legislated combat agency for flooding in New South Wales and is responsible for planning for and conducting the warning and evacuation of communities at risk from floods, including floods affected by dams. The successful execution of these responsibilities is dependent upon the continuing development of a strong, cooperative relationship between the dam owners and managers, dam regulators and emergency managers and the effective incorporation of community expectations in dam safety planning.
This paper explores some of the ways that this relationship can help to meet well accepted community expectations in respect of risk to life and property and outlines progress made in dam safety planning to date. The emergency response aspect of dam failure planning is still a relatively immature field in Australia, and it follows that there are lessons to be learned as we proceed. In that context, the paper also describes some of the difficulties the State Emergency Service has encountered in its role as the response planning agency and suggests some guiding principles to enhance future interactions between the key stakeholders.
Martin Pinkham, Robin Dawson, John Grimston
Resource consents for Christchurch’s existing solid waste disposal facility at Burwood expire in May 2005 and the landfill must close. A new, state-of-the-art regional landfill is under construction at Kate Valley, which will accept solid waste from Christchurch and surrounding districts. Investigations and studies for the landfill have attracted considerable public attention, engaging public groups in discussions through resource consent hearings in 2002 and 2003.
The proposed landfill includes two embankment dams in a cascade arrangement below the landfill. The first is a 19m high sedimentation dam designed to retain silt runoff from the earthworks associated with landfill construction and operation, protecting the health of the stream and environment below the dam. The second is a 9m high dam performing dual roles of storing and supplying water for the landfill earthworks activities, and providing an additional safety buffer for silt control and containment of any accidental release of leachate at the landfill.
While the dams are relatively modest in size, they are being built to very high standards with strict peer review as a result of their association with the landfill project, and to minimise any community and environmental impacts. The design and construction of the landfill and dams is being completed using an innovative modified alliancing arrangement which provides the close working relationship that alliances are renowned for, while minimising up-front financial risk to the owner.
This paper deals with key aspects related to the landfill dams, such as community consultation and expectations, environmental impacts as well as the technical features. Construction is underway for the dams and the landfill at the time of writing of this paper.
Brian Simmons, Glen Hobbs, S Muralitharan, Udaya Peeligama
Warragamba Dam supplies up to 80% of Sydney’s water needs and is currently undergoing a range of major infrastructure upgrades. The outlet works upgrade is one of these projects. The outlet works of the dam were constructed in the 1950s and consisted of four 2100mm pipes with isolating gate valves and needle control valves feeding two large aboveground pipelines running 27 kilometres east to Prospect Reservoir in Sydney’s western suburbs.
In the 1990s the then dam owner (Sydney Water) undertook a detailed and extensive risk analysis of the outlet works. The study resulted in a recommendation to remove the existing valves and replace them with a combination of emergency closure (guard) valves and isolating valves. Under the Sydney Catchment Authority (the present dam owner) work subsequently proceeded in 2004 as a design and construct contract with all aspects of construction and water supply risks identified. Stringent controls were developed and placed on work programs and pipeline shutdowns to ensure the safety of all involved and the integrity of the supply to Sydney.
The four outlets required eight large valves, which were manufactured in Germany and were required to meet stringent operational requirements.At the time of writing three of the four outlets have been successfully upgraded and commissioned.Work has commenced on upgrading the fourth outlet, which is due for completion by the time of the conference, approximately 20 months ahead of schedule.
This paper discusses the project from the initiation of the risk analysis study, through the consideration of options, development of the contract, and the supply, installation and commissioning of the large valves and pipe work. It highlights the role of risk assessment in selection of the preferred option and addresses some of the engineering challenges faced during the project.