Chriselyn Kavanagh, David Stephens, Peter Hill
Two-dimensional hydraulic models are now widely used to simulate flooding downstream of dams as part of dambreak assessment studies. These models provide high resolution information on velocity distribution across the floodplain, which is of paramount importance to accurate estimation of the depth-velocity product required when undertaking loss of life assessments. In addition, the outputs from these models are much more readily presented as maps and animations, which can be an important tool in the dam safety emergency planning process.
Recently, the United States Army Corps of Engineers released a new version of the popular hydraulic model HEC-RAS which includes the ability to conduct two-dimensional simulations. Other widely used two-dimensional models include DHI’s MIKE suite and TUFLOW. This paper presents a review of the capability, functionality and useability of these models for the specific purpose of dambreak modelling. Key features considered as part of the review include model stability, run times, methods of simulating dam breaches, outputs and the ability to link to loss of life simulation models. A case study comparing the performance of three commonly applied models is presented and discussed, and advice is provided on model selection.
Dr Matthew Sentry, Nabeel Elias
Although permanent ground anchor technology has advanced in leaps and bounds over the past two decades, the focus of anchor technology has been on developing techniques to minimise the risk of component and system failure due to corrosion. The advancements in structural materials available in the market in recent years have enabled research into alternative materials for permanent ground anchor systems.
Carbon fibre has become a significant structural alternative throughout North America for bridge and building construction as well as repair and structural strengthening of deteriorated/corroded structures. These advancements and the necessity to investigate alternative materials for anchor systems have led to research in understanding the long term performance effects of using carbon fibre products as an alternative to steel tendons in permanent ground anchors.
Following on from the advanced research works at Monash University and Geotechnical Engineering which investigated the durability performance of various available CFRP strands when used as an alternative to conventional steel tendons in permanent ground anchor systems, Geotech developed the first post tensioned ground anchor system using CFRP strand.
Following laboratory based trials and small scale bun barrel tests, Geotech was able to successfully design, construct, install and stress the first 27 strand post tensioned CFRP ground anchor installed into Yass Dam. The CFRP strand was stressed and locked off at 4,000kN. Real time monitoring has been installed to monitor the load throughout the anchors service life.
This paper provides the details of the construction, installation and stressing of the first CFRP anchor installed into a dam structure.
Kelly Maslin, Richard Rodd
As an industry there have been many advances in the assessment of the probability of failure associated with a range of failure modes including embankment piping and stability. However, little work has been done on the development of a meaningful tool to assist in the assessment of probabilities of failure for embankment breach due to overtopping.
In the development of this paper a number of embankment overtopping case studies were reviewed and these were used to anchor the suggested probabilities of failure. The case studies assessed were all low to medium height, homogeneous earthfill embankment dams. Consideration has been given to a range of factors including embankment material and construction, embankment geometry, duration of overtopping and the presence and condition of vegetation on the embankment face.
The results of the analysis of the case studies indicate that the probability of breach due to overtopping, particularly for short duration events, is actually relatively low compared to the typical values being adopted within the industry.
It is the intended purpose of this paper that it provides guidance to the industry on the assignment of the probability of embankment breach due to overtopping to allow more consistent, robust and defensible estimates for dam safety risk assessments.
Amanda Ament, Thomas Ewing, Frank Nitzsche
The automatic operating buoyancy type spillway gates at Lenthall Dam did not operate properly since installation. This paper discusses the problems encountered, the investigation conducted using computational fluid dynamics to quantify the problems and develop solutions. It describes the design of the modifications to the gate and flow regime and results after construction.
Russell Mills PhD,Rebecca Freeman, Malcolm Barker
The global mining industry lives with the risk of catastrophic events such as water storage or tailings dam failures as part of its daily operations, and has developed a number of approaches to enable mine management to understand the nature of the risks and the ways in which they are being managed. One such approach involves the use of bowties for the understanding of the hazards and risks. Building from bowties, the second approach involves the selection and management of controls critical to the prevention or mitigation of the catastrophic event. The Australian mining industry is a world leader in this regard and the purpose of this paper is to illustrate how bowties are constructed, how risks can be semi-quantitatively estimated, how critical controls are selected and managed, and how, if all this is done well, risks can be demonstrated to be as low as reasonably practicable (ALARP).
This paper sets out key themes and presents an example for a tailings dam failure to illustrate the role of bowties and critical controls in management of catastrophic events. It will also highlight the role of bowties in the anticipated introduction of a Safety Case approach to dam risk management. Bowties provide a useful tool for the transfer of risk management knowledge from the designer, to allow dam owner / operators to better understand their risks and to recognise the link between design and operational controls and how they are used to manage those risks to ALARP.
The key differences between probabilistic seismic hazard analysis (PSHA) and deterministic seismic hazard analysis (DSHA, preferably referred to as a scenario-based analysis) are that, unlike DSHA, PSHA takes account of all magnitudes on all earthquake sources that may affect the site, including the frequency of occurrence of each earthquake scenario that is considered, and fully considers the random variability (epsilon) in ground motion level. The result of a DSHA is the ground motion at the site resulting from a single earthquake scenario (or a few scenarios) having a preselected value of epsilon (usually 0 or 1), and the annual frequency of exceedance (or return period) of this ground motion level is undefined. In contrast, the hazard curve produced by PSHA yields the mean annual rates of exceedance (or return period) for each ground motion level. The complementary nature of PSHA and DSHA is manifested in the fact that practical application of PSHA, especially using ground motion time histories, results in scenario earthquakes that resemble the products of DSHA. Application of the period dependence of epsilon using the conditional mean spectrum (CMS) avoids the inaccurate and overconservative representation of the hazard by the uniform hazard spectrum (UHS) obtained in PSHA.