Ryan Singh, Jiri Herza, James Thorp, Michael Ashley
Performance-based risk-informed decision making is an underlying principle of the Global Industry
Standard on Tailings Management (GISTM). While owners make significant efforts to align with this
principle, commonly used risk assessment and management practices in the mining industry have largely been based on the HSE principles, which consider more frequent, lower consequence incidents.
As a result, the existing risk assessment frameworks do not provide the owners with a comprehensive understanding of the risk profiles of their tailings storage facilities (TSFs). Without the understanding of a facility’s risk profile, the owners cannot appreciate how changes to their facility, processes and operational activities may impact the risk profile. A large step-change in thinking is therefore required in risk assessment practices for the owner to align their TSF management with GISTM requirements.
Beyond risk assessments, the mining industry has other valuable concepts to manage the safety of their tailings management practices, such as Critical Controls, however, commonly used risk assessment and management practices do not incorporate these concepts.
This paper explores commonly used risk assessment practices and the concepts of Critical Controls. It proposes how these concepts can be linked, with Critical Controls being embedded in the risk assessment process. The outcomes of linking these concepts result in an estimation of the effectiveness of the Critical Controls and how they can be improved to demonstrably reduce the risk presented by a TSF. A case study has been included to demonstrate the benefits of linking risk assessment with Critical Controls and how owners can readily identify deficiencies and efficiently manage the risk profiles of their facilities.
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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,
Mark Pearse, Mark Foster, Peter Hill, Sam Banzi, Muhammad Hameed, Benson Liu
Determining which risk control measures are required is one of the top issues for dam owners as they contend with limited resources generally and capex in particular. The key issue addressed in this paper is how a dam owner can both identify the control measures that they should implement and demonstrate that they are acting reasonably and responsibly. The Framework developed in this paper provides a practical and transparent way to address the relevant matters that are required to be considered under common law, work, health and safety (WHS) legislation and the NSW Dams Safety legislation for determining whether a risk control measure is reasonably practicable. It provides dam owners with a transparent and defensible way of both identifying the controls and demonstrating that they are acting in a reasonable and responsible manner.
David Reid, Andy Fourie, Riccardo Fanni, Cristina Vulpe, Alexandra Halliday
Recent failures of a number of tailings storage facilities (TSFs) has highlighted the need for better
governance and operational management of these structures. One means to improve their safety is clearly better and more focussed monitoring. Significant efforts are underway in this area, with a number of technologies being deployed. In particular, the monitoring of deformations through a variety of means (direct, satellite inferred) is increasingly being applied. While deformation monitoring to warn against failure has a long history in geotechnical engineering, some aspects of the rapid triggering and resulting flow of some TSFs may not be amenable to deformation monitoring, in the sense that actionable warning of an impending failure is not assured.
To examine this issue, a series of numerical models of an idealised TSF are carried out. This idealised TSF is brought to failure by means of a rising phreatic surface – often referred to as the constant shear drained (CSD) stress path. Deformations of the outer slope and crest of the numerical model – i.e. those that could be monitored for a real TSF – are tracked and analyses for the models carried out. It is seen that under CSD loading distinct deformation patterns indicative of impending failure are not always clear. Rather, minimal deformations and indeed swelling of the crest is seen leading to failure. The importance of recognising the minimal pre-failure deformation patterns that may manifest with a rising phreatic surface is noted.
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.
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.