The tailings deposition management plan (TDMP) provides the methodology for optimal deposition of tailings slurry. It forms an integral part of the design of a tailings storage facility (TSF). This paper focuses on subaerial (air-dried) tailings deposition, which is extensively utilised within Australia.
The correct implementation of the TDMP determines the condition of the tailings deposit in terms of trapped moisture, deposited dry density (which directly affects storage capacity), saturation/excess pore pressure (which influences static liquefaction), strength/stability (risk), the deposited beach slope and the difficulty/cost of rehabilitation. Correct design and implementation of the TDMP is necessary to achieve the design requirements, to reduce risk, and to enable cost-effective rehabilitation.
Once implemented, the TDMP is validated by observation and adjustment of spigot discharge duration (per spigot in some cases) and the number/location of spigots to provide the required beach shape to minimise the pond area in the TSF. This in turn maximises deposited dry density and hence TSF storage, increases flood routing capability, reduces risk of static liquefaction, non-compliant discharges/overtopping and high rehabilitation costs.
Other aspects of the deposition which are recorded during this process include channel erosion and incorrect beach slope which are often due to spigot type, the number of spigots open and/or decrease in percent solids of the tailings. The first two aspects are handled by operator training, the third will require a revision of the TDMP as a ‘change management’ measure.
This paper presents the testing conducted and typical results for a metalliferous mine in western NSW (site unnamed) showing the most recent implementation of the TDMP design. This TDMP is about to be implemented. The paper also presents a case study for a coal tailings TSF in the Western Coalfields of NSW west of Lithgow (site unnamed), which has successfully been implemented and achieved deposited subaerial beaching meeting the required (estimated density) as per the TDMP design.

Minerals Council of Australia (MCA) has adopted the Towards Sustainable Mining® (TSM®) system in recognition of evolving community expectations of the Australian minerals industry’s environmental, social and governance (ESG) performance. TSM was established by the Mining Association of Canada (MAC) and is recognised globally with adoption in 11 countries.

TSM builds on existing industry commitments in Enduring Value – the Australian minerals sustainable development framework – by providing a consistent approach to assess, demonstrate and communicate site level performance in a transparent and accountable way, building community confidence and trust. TSM protocols have been adapted to suit the Australian context through the inclusion of local guidance, reference to regulatory requirements and input from key industry stakeholders.

Tailings management has been central to the TSM program since its inception in 2004. The MAC Tailings Guide and the Operation, Maintenance and Surveillance Manual (OMS) Guide pre-date TSM, having been introduced in 1998 and 2003, respectively. The TSM requirements and guidance for tailings management provide a systematic approach to tailings management enabling companies to benchmark against good practice, supporting improved performance. Tailings requirements have continued to improve. For example, significant revisions were completed after the 2014 failure at the Mount Polley Mine in Canada, which was informed by an independent review.

Following the release of the Global Industry Standard for Tailings Management (GISTM), MAC undertook a gap analysis that informed further improvements while noting there is a high degree of alignment between TSM and the GISTM. TSM takes an integrated approach, helping to ensure a systematic, holistic approach to tailings management. TSM also has well-established tools for detailed performance criteria, reporting, and third-party verification, providing a high level of rigour.

Slope stability analyses using the ‘Factor of Safety’ (FoS) approach have been considered as a main method in the industry when assessing the stability of tailings storage facilities (TSFs). Typically, risk mitigation measures and actions are recommended where the FoS for a slope is less than the values recommended by (ANCOLD, 2019), based on deterministic limit equilibrium (LE) modelling.
The deterministic LE modelling undertaken for the TSF considered in this paper indicated additional buttressing was required to meet minimum FoS requirements for future embankment raises. This paper presents a case study where a quantitative risk assessment (QRA) approach was used to estimate the probability of failure (p[F]) for the same TSF slope, with the intent to demonstrate that the risks are acceptable without additional buttressing.
Various triggers for slope instability were identified and fault trees developed to support estimates of the likelihood of each of these events occurring. The p[F] for each of these triggering events was estimated based on the product of the probability the event occurring, the probability slope instability would trigger given the trigger occurs and the p[F] from stability modelling for each condition. The potential loss of life (PLL) was assessed based on a time-based risk exposure based on discussions with the site owner.
The assessment indicated the TSF would remain in the zone where risks are tolerable only if they satisfy the ‘As Low As Reasonably Practicable’ (ALARP) principle, as per the f-N chart from the ANCOLD risk guidelines (2022) for ‘New Dams’. The QRA results indicated that no additional buttressing was required for the next embankment raise as the TSF remained in the broadly acceptable zone indicated by (ANCOLD, 2022). Additional studies, including a numerical deformation model, were recommended to further assess the likelihood of catastrophic release of tailings under the triggers considered in the QRA and to identify if other reasonably practicable risk reduction measures could be installed.

This paper presents a retrospective commentary of two case studies of the Engineer of Record (EOR) role in the context of projects undertaken within a ‘capital project’ framework and presents areas of the process that could be improved in the context of dam safety. The capital project framework is largely focused on proving the feasibility of a project and gaining funding approval, with motives such as accurate cost estimation and value optimisation, where the design consultant is primarily encouraged to demonstrate solutions that reduce capital expenditure. A feasible, compliant design is required but risk management design improvements are typically only considered if there is an accompanying cost reduction. Under this focus, the role of EOR (as defined by the Global Industry Standard on Tailings Management (GISTM) by the International Council on Mining and Metals (ICMM, 2020)) is often to confirm alignment with standards, with the integrity of the facility during design, construction, operations and closure having a diminished focus.

The first case study was for detailed design of an embankment raise to a TSF where the author was the study lead and the EOR was from the same consultancy as the author. Two design features are discussed. One feature reduced risk but added cost. The second feature reduced costs for the embankment raise, increased tailings and flood storage capacity, but resulted in a perceived increase in the risk profile to the owner. The case study demonstrates that the value optimisation framework needs improvement to consider risks and the EOR’s perspective.

The second case study was for a design of a buttress around an upstream raised TSF where the author was the study lead and the EOR was from another consulting firm. An example is discussed where the author’s team proposed solutions they considered would significantly reduce capital expenditure, whilst maintaining the integrity of the facility, that were ultimately not endorsed by the EOR at the time of publication. The case study demonstrates that, in the author’s view, the design of a TSF, and any improvements, should be undertaken by the EOR. However, where this is not feasible, due to resource constraints or other reasons, the capital project framework needs to improve how the design consultant is able to interact with the EOR and the owner to achieve a ‘best for project’ outcome.

A significant spoil pile failure occurred at Goonyella Riverside Mine in the Bowen Basin Coalfields of Queensland, Australia, between 1 and 5 July 2022. The spoil pile consisted primarily of Tertiary silts and clays excavated from the adjacent pit and occurred during a rainfall event that was preceded by several large rainfall events over the 24 months prior to the failure. These rainfall events led to the wetting up and degradation of the silty and clayey spoil, forming soft layers. The failure was captured using various instruments and field monitoring techniques. It was concluded that wet spoil layers with high clay mineral content behaving undrained during shearing played a key role in the failure. The failure has been the subject of back-analysis using the finite element method, sampling and laboratory testing, and a piezocone investigation, aimed at understanding the degradation and strength loss on wetting up of the clay mineral-rich spoil and preventing similar failures in the future. The paper describes the construction and composition of the spoil pile, the impact of rainfall events, the failure, and the results of the investigations. The investigations have led to an improved understanding of the degradation and strength loss of the clay mineral-rich spoil. Recommendations are made to prevent similar failures occurring in the future.

The value of good planning is undeniable; however, it can be challenging to know exactly what to plan for. In the case of a tailings facility, the list of potential changes that may occur over the life of a project can be long and convoluted. Deposition rates, wall raises, alternate flow paths, changes in ore mineralogy, and technology advances can all significantly impact operations.
The design of tailings infrastructure, such as pumps, piping, power supply and control systems, does not often receive the same level of rigour as the design of the dams or upstream processing plants. Often, these systems are designed to manage a specific set of conditions with limited flexibility. This can lead to cases where significant investment in retrospective upgrades is required.
However, decisions can be made in the design phase to improve the flexibility of tailings infrastructure systems and assist with future-proofing the operation. This paper outlines common pitfalls encountered in tailings and decant return infrastructure design and presents mitigation strategies that can be used to avoid these. Examples of this include the installation of multiple tailings pipelines, selection of piping materials, sizes and rating, pump selection, and capacity requirements for electrical and control system infrastructure.
The paper also presents the economic case for strategic investment in key areas by considering different upgrade scenarios across the project’s life. These scenarios and the costs shown are based on the authors’ experience across several projects of this type.

The last decade has been characterised by some of the worst environmental and loss-of-life disasters in the history of tailings dam failures. As a result, the Global Industry Standard on Tailings Management (GISTM) has been introduced as a multi-stakeholder effort to prevent future tailings storage facilities (TSF) related disasters from happening again. Many mining companies, ICMM (International Council on Mining and Metals) members and non-members have committed to comply with the Standard.

Operationalising this governance framework will require regular self-assessments to identify and manage gaps toward standard compliance. In that respect, different requirements are provided for implementing and auditing the standard. This undertaking, combined with the additional effort to comply with jurisdictional legal requirements, other standards and guidelines as well as internal policies can be extensive and resource laden.
Even though there are many requirements derived from all these standards-related demands, there are also many resemblances. In that direction, Vale has taken this challenge as an opportunity to streamline the efforts and, in collaboration with Forwood Safety, built a platform to simplify the compliance journey against multiple standards.

This paper presents an innovative approach to merge requirements from multiple standards into a single integrated verification process, thereby reducing the number of assessments and introducing a new attempt to differentiate the best practice from standard practice. The equivalency study completed by ICMM and MAC (Mining Association of Canada) as well as Vale’s internal normative documents and local regulatory compliance were used to develop this solution.

Vale also designed an active action management approach to link the resulting action plans from the gap analyses with the compliance score, gaining real-time compliance visibility, allowing the system to forecast when a TSF will be 100 per cent compliant against the chosen standard.