Chris Nielsen, Irene Buckman
As individuals, we are concerned about how a risk affects us and the things we value
personally. We may be willing to live with a risk if it secures us certain benefits and if the
risk is kept low and clearly controlled. We are less tolerant of risks over which we have little
ANCOLD’s risk assessment guideline (2003) identifies an individual risk threshold as being
one where “the dam safety risk to an individual should be close to the average background
risk of the population”. This is a principle of equity, where “all individuals have
unconditional rights to certain levels of protection” (HSE, 2001). The definition of
population at risk applied to Queensland’s referable dams (DNRME, 2018), being
individuals within a residence or workplace and typically not participating in any risky
activities such as driving a vehicle or walking through flooded waters, provides further
justification of this right.
In practice addressing societal risk tolerances and duty of care considerations may result in
individual risks being substantially lower than the thresholds. This may not always be the
case and, irrespective, should not distort the purpose of the individual risk tolerance test;
the principle of equity that drives individual risk tolerability has foundations in our societal
values and is easily and widely understood as a core value. This should be succinctly
described when justifying expenditure on risky infrastructure such as dams.
This poster describes aspects to consider when selecting a threshold individual risk
tolerance. Subject to site-specific considerations of the particular age group of individuals
most at risk, the wider benefit of the dam to society and ALARP, a single threshold
individual risk tolerance of less than 10-5 per annum (or 1 in 100,000 years) would appear
The aspects described are elaborated in the revised Guidelines on Safety Standards for
Referable Dams, soon to be published on the Queensland Government website (RDMW,
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Now showing 1-12 of 37 3483:
Dr Mark Leonard
The quantification of the 85% and 95% hazard fractiles, as required by the ANCOLD 2019 Guidelines for design of dams, is investigated. It is found that there are four independent sources of uncertainty in the PSHA input models that have a significant effect on the hazard. So all four need to be quantified, particularly for Extreme and High A consequent dams. It is also found that the uncertainty of many of the other parameters, which are routinely included in probabilistic seismic hazard assessments, have minimal effect on either the mean or the higher fractiles so do not necessarily need to be routinely included. The complexity of the input models required to satisfy the new standards are substantially higher than those routinely used in prior decades.
Jarrad Coffey and John Plunkett
As tailings standards continue to evolve, a greater focus is being placed on the monitoring of tailings storage facilities (TSFs). While this is a positive development for TSF safety into the future, it is only one component of the work required to implement Performance Based Risk Informed (PBRI) management. There is also a significant human element that can be aided by reducing the time spent of personnel sourcing/aggregating data and instead focussing on decision making. It is discussed in this paper how a more holistic approach to monitoring via a dashboard that displays all management data relevant to a portfolio of TSFs can be applied in parallel to risk assessment to work towards the goal of PBRI. The dashboard also facilitates review and governance activities, which are central to the Global Industry Standard on Tailings Management. An example of the dashboard utilised at Rio Tinto Iron Ore is presented to provide an example of such a system and its benefits.
Reza Asadi, Mahdi M. Disfani, Behrooz Ghahreman-Nejad
Rockfill, a granular material with particle sizes usually in the range of 2 cm to 1 m, is commonly used as the main construction material in a range of civil engineering applications such as water and tailings retaining embankment dams. Rockfill’s complex behaviour mainly stems from its inherently large particle size grading on one hand and its discrete and heterogeneous nature on the other hand. The investigation of mechanical behaviour of rockfill requires expensive and time-consuming laboratory testing in large apparatuses, which are scarce. This highlights the importance of numerical investigation techniques such as Discrete Element Method (DEM) in better understanding of rockfill properties. In this paper initially a concise and comprehensive overview of effective parameters on Rockfill behaviour are presented followed by the discussion on analytical and numerical methods for investigation of the mechanical behaviour of Rockfill.
Finally, a combination of Replacement and Bonded-Particles (clusters) methods is proposed so the effects of particle shape and breakage, which are among the most effective parameters, can be adequately investigated. The preliminary results of DEM modelling are also presented which show a good agreement with the expected micro-mechanical behaviour of rockfill.
Anna Hams, Lindsay Millard, Elizabeth Jackson, Zara Bostock, Helena Sutherland
The Queensland dam regulator requires that dam safety risk during construction must not increase from its existing profile. The Stage 2A upgrade of Ewen Maddock Dam required excavation of its homogeneous embankment to retrofit chimney and filter blankets, and also the construction of a concrete parapet wall. Due to the constraints of the embankment profile and a constricted site, it was necessary to excavate the downstream face of the embankment. This excavation increased the risk of embankment failure due to overtopping, piping and instability. This paper discusses the measures taken to manage those dam safety risks, and includes:
● use of a temporary system consisting of six large siphons to regulate the lake level to a Restricted Full Supply Level (Restricted FSL). This encompassed the optimisation of lake level and capacity of siphons required to balance competing risks; dam safety, environmental, community and water security. This optimisation was based on a probabilistic assessment of hydrological inflows and lake levels, the development of a flow management plan;
● implementation of a Dam Safety Management Plan which outlined the roles and responsibilities for
managing dam safety during construction at each pre-determined lake level trigger levels. This includes how the contractor was involved to ensure quick response from the “eyes and ears on the ground”; and,
● development of recommended construction methodologies including a “rolling front” and placing
filters vertically to increase production, maintain quality and limit the extent of embankment excavation underway.
Olle Wennstrom, Andrew White
Over the last few years tailings dams have come under increased scrutiny, partly due to two highly publicised TSF failures in South America, but also because of several other incidents in Australia and elsewhere in the world. As investors came under pressure to positively impact the projects they financed, the Global Industry Standard on Tailings Management (GISTM) was released in August 2020.
Topic 5 of GISTM, “Emergency response and long-term recovery”, comprises Principle 13: “Prepare for emergency response to tailings facility failures” and Principle 14: “Prepare for long-term recovery in the event of catastrophic failure”. The topic further introduces the term “Emergency Preparedness and Response Plan” (EPRP).
This paper explains what the term “Emergency Preparedness” means and how the owner/operator of a mine can achieve it. The paper also delivers a concept for long-term recovery planning.