The National Seismic Hazard Assessment 2018 (NSHA 18) project intends to revise the existing seismic hazard map (AS1170.4 2007) for Australia. Geoscience Australia (GA) are leading the project along with a consortium of seismologists, geologists and earthquake engineers.
The NSHA 18, due to be released in 2018 is of great importance to dam owners and operators. The project intends to incorporate a comprehensive approach to seismic hazard, particularly in modelling uncertainty and variability.
The Global Earthquake Model (GEM) is an international consortium of scientists, engineers and policy makers. One of the primary aims of GEM is to provide a uniform set of tools for analysis in seismic hazard and risk. GEM was established to provide a framework for global standards in comparing risk analysis, awareness and actions in an effort to increase resilience to vulnerable communities.
The NSHA 18 will use the GEM framework in order to meet its own objectives for the new upcoming hazard map. The Seismology Research Centre will contribute to the NSHA 18 in three areas. Firstly, to produce a unified earthquake catalogue where GA will homogenise magnitudes to a uniform scale. Secondly, to produce a number of applicable alternate seismotectonic models, and thirdly, through the contribution of ground motion data collected over the last forty years within Australia.
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Matthew Ind, Kate Brand and Mark Ferrier
The framework for undertaking a dam breach analysis for water dams is reasonably well established with a depth of information and software available to guide practitioners on a consistent approach to undertaking failure impact assessments. In contrast, dam breach modelling for tailings dams is currently a developing field with a wide range of modelling approaches taken and an inconsistency in the quality of the failure impact assessments undertaken. Recent tailings dam failures at the Mt Polley Mine in British Columbia, Canada and the Fundäo and Santarém dams at the Samarco iron ore operation in Minas Gerais, Brazil have provided a sobering reminder of the hazards presented by tailings dams and the clean-up challenges that are significantly more complex than a similar failure of a water dam.
Current guidelines and approaches to dam breach modelling are often done assuming the run-out material from the breach is just water without due consideration of the impact from tailings loss. There is limited analysis undertaken on credible failure modes of tailings dams with an assumption that the embankment just “breaks” at some random point without appreciation of the failure mechanism. The misunderstanding of failure modes leads onto inconsistencies with application on whether a ‘sunny-day’ or extreme flood event modelling should be applied, with one or the other selected without explanation.
This paper outlines a framework that can be applied when undertaking a dam breach study for tailings dams to enable a consistent and credible assessment of potential failure impacts. The following tasks are discussed in detail in support of this framework:
Kate Brand, Matthew Ind
Failure impact assessments of tailings dams are largely pre-determined by the input assumptions and, due to lack of supporting data, the results can be highly subjective. Despite numerous guidelines available for undertaking failure impact assessments of water dams, there are very few technical guidelines on how to form the above assumptions and how to undertake dam breach modelling of a tailings storage facility (TSF).
Tailings dam failure databases are limited, with the available information generally not analogous with the TSF under assessment, especially given the rising volume and height of modern tailings dams. ‘Rule of thumb’ methods are often referred to, with a percentage of tailings and water assumed to be discharged along with assumptions of the breach height and width made.
Using a case study, this paper compares a range of potential failure impact assessments generated using typical methods of analysis and runout modelling to demonstrate the reliance on engineering judgement in failure impact assessments. Given the subjectivity observed within the results, consideration should to be given to the level of reliance on tailings dam failure impact assessments in formulating emergency action plans. It is recommended that regulators take an active role in formulating tailings dam impact assessment guidelines.
Jason Needham, John Sorensen, Dennis Mileti, Simon Lang
The potential loss of life from floods, including those caused by dam failure, is sensitive to assumptions about warning and evacuation of the population at risk. Therefore, the U.S. Army Corps of Engineers engaged with social scientists to better understand the process of warning and mobilizing communities that experience severe flooding. This improved understanding enables dam owners to better assess the existing risk posed by their assets and investigate non-structural risk reduction measures alongside structural upgrades.
In this paper, the U.S. Army Corps of Engineers research is summarised to provide general guidance on the warning and mobilization of populations at risk for practitioners assessing the potential loss of life from dam failure. This includes commentary and quantification of three primary timeframes: warning issuance delay, warning diffusion, and protective action initiation. A questionnaire for estimating these parameters is also introduced, alongside a case study application for an Australian dam.
This paper also summarises the current understanding of how to reduce delays in determining when to issue warnings, increase speed at which warnings spread through communities, and decrease the time people spend before taking the recommended protective action. These insights will help all people involved with emergency management, including those tasked with developing Dam Safety Emergency Plans.
There is a significant body of knowledge in relation to assessing the impacts of earthquakes on earth and rock fill dams which has led to a number of widely recognised and accepted methodologies for the calculation of potential deformations from an earthquake event. However, limited research has been conducted into the assessment of blasting impacts on earth structures. This has led to an adoption of earthquake analysis methods in the assessment of blasting impacts on earth structures without adequate consideration to the difference between the stresses and displacements imposed on an embankment as a result of a blast as opposed to an earthquake. Adopting earthquake analysis techniques may result in conservative vibration limits being imposed when undertaking blasting near embankment dams which may have negative financial impacts.
This paper explores the risks associated with blasting adjacent to earth fill dams and details the difference between stresses and displacements imposed on an embankment by a blast versus an earthquake.
This paper also discusses previously adopted approaches to assessing potential impacts associated with blasting and the limitations associated with adopting a pseudo-static and simplified permanent deformation analysis for blasts modelled as equivalent earthquakes. Finally, the paper proposes an alternate risk based analysis approach.
Woodrow Lee Fields
Although flooding can lead to many types of severe consequences, the primary objective of the US Army Corps of Engineers (USACE) dam and levee safety programs are to manage risk to the public who rely on those structures to keep them reasonably safe from flooding. Thus, reducing the risk associated with loss of life is paramount. This paper discusses new methods that have been developed for estimating life loss with uncertainty from flood events.
HEC-LifeSim is a dynamic simulation system for estimating life loss with the fundamental intent to simulate population redistribution during an evacuation in conjunction with flood wave propagation. The population redistribution process has been revised from the ground up as an agent based model. In addition to the agent based model, uncertainty analysis has been enhanced. Through Monte Carlo sampling, the natural variability of warning and mobilization timing and likelihood of fatality varies delivering a range of potential life loss from a hazard. Knowledge uncertainty about parameters, such as warning issuance time, can also be defined. To accommodate the new HEC-LifeSim computation engine, an innovative GIS interface has been developed to quickly summarize and animate results. The methods that are discussed in the following provide new tools to estimate life loss and educate local authorities.