Design acceptance criteria for operating open-pit slopes: An update

Macciotta, Renato; Creighton, Ashley; Martin, C. Derek

doi:10.1080/19236026.2020.1826830

Cited by 9 publications

(8 citation statements)

References 24 publications

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“…The challenges can be attributed to several factors, including (but not limited to) rock mass uncertainty, spatial variability, geological complexity, data availability etc. Key sources of uncertainty (following from Macciotta et al 2020) include the geological/geotechnical/hydrogeological models, spatial variability of relevant input properties, applicability of strength criteria, laboratory testing adequacy (scale and bias error), methods of analysis, and human error.…”

Section: Assessment and Communication Of Riskmentioning

confidence: 99%

Critical challenges impacting the advancement of slope design reliability

Moffitt

2023

SSIM 2023: Third International Slope Stability in Mining Conference

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There have been many recent and ongoing advances in the area of slope stability, including tools and processes for slope management, rock mass characterisation, stability assessments, and selection of design acceptance criteria. Despite the many advances and ongoing research in the field, there remain several fundamental unresolved challenges that impact the design and assessment of pit wall stability. In this paper, these have been categorised into six key areas:• Assessment and communication of risk: a risk-based approach to slope design has become more common practice, particularly with advances in approaches to calculating a Probability of Failure (PoF). However, the PoF is not quantified in a consistent manner within our industry and can present a false or misleading view of project risk to stakeholders and decision-makers.• Reliance on technology: new and emerging technologies have provided many benefits to our industry but, in some cases, technology has advanced faster than the ability to answer more fundamental and basic questions related to material characterisation and slope behaviour.• Treatment of damage/overbreak zone: the rock mass strength and hydraulic conductivity of the near-surface 'rind' around the pit wall is impacted by damage resulting from blasting and stress relaxation. The depth and extent of damage/disturbance are very difficult to test/evaluate. Although the assumptions may significantly influence predictions of inter-ramp scale Factors of Safety (FoS), there are no consistent approaches or standards for the treatment of this zone in stability analyses.• Integration/communication: within our complex mining environments, disconnects often exist between disciplines but also between the technical teams, management and stakeholders.There are also obstacles to information sharing and collaboration. These can reduce efficiency, design reliability, and the speed of innovation.• Increased demand for minerals: electrification and the demand for resources are arguably greater than they have ever been. With this increase in demand comes additional challenges related to developing deeper mines and steeper pit walls in increasingly remote environments.• Reducing technical workforce: the industry is currently under-resourced. The talent pool is shrinking while mine complexity is increasing. It is critical that the industry take steps in the short term to address this skills shortage.This paper is not intended to prescribe or present solutions to these issues. Rather it is intended as a means to engage and challenge the industry to discuss and consider these issues. Based on research along with the author's experience and discussions with industry leaders, this paper explores each of these issues, how they may impact the reliability of slope designs, and ideas for consideration to move the industry along a path to overcoming these challenges.

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Section: Assessment and Communication Of Riskmentioning

confidence: 99%

Critical challenges impacting the advancement of slope design reliability

Moffitt

2023

SSIM 2023: Third International Slope Stability in Mining Conference

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“…Another issue of concern for directly applying typical FoS criteria recommended for operations for defining mine closure completion acceptance thresholds is that such FoS limits, particularly where data uncertainty is high, cannot reliably be directly interpreted as an indication of PoF. This has been shown by Macciotta et al (2020) for operating open pit DACs, where data reliability will likely be higher than for closure, where greater longevity is required, and hence where assessing more extreme value statistics becomes a necessity.…”

Section: Design Service Lifementioning

confidence: 99%

“…This concept is not new and is discussed in a study and operational context in many references, including Adams (2015), Hawley & Cunning (2017) and Macciotta et al (2020). Nevertheless, because of the significant difference in perspective between operations and closure and the typical complexity of most large pit slopes, as schematically illustrated in the left diagram in Figure 8, significant inherent variability must be accounted for as potentially existing throughout the slopes.…”

Section: Stability Evaluationmentioning

confidence: 99%

“…In concept, the first two ranking scales, Cf and Cq, mirror the classic confidence-consequence assessment approach outlined in Macciotta et al (2020), with the relative consequence scaled based on the notes shown around the perimeter of the hypothetical pit plan in Figure 8. Including the third dimension of the wall condition per Table 3 allows ready assessment of sectors requiring attention, as summarised in Table 4.…”

Section: Stability Evaluationmentioning

confidence: 99%

See 1 more Smart Citation

Transitioning from mine operations to closure: the dilemma of differing geotechnical design acceptance criteria perspectives

Carter¹,

Graaf²,

Dixon³

et al. 2022

Mine Closure 2022: 15th Conference on Mine Closure

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For open pit mining, understanding and managing slope performance is critical for both operations and closure. Towards the end of mine life, achieving reliability of slope performance in operations often necessitates real-time implementation of active slope stabilisation controls. This situation changes significantly towards closure, when production economics are no longer the priority, and resources for field monitoring control and active slope management diminish. The risk profile also shifts to a greater focus on stakeholder needs, including the environment and social acceptance, as land use changes. Although risk profiles will shift, the safety goal of 'zero harm' needs to continue to be achieved through all phases.Historically, most final pit slopes were not designed for closure. Rather, they tended to be optimised for production efficiency and thus were typically too steep for long-term reliability. The key question then becomes -what happens when the controls that have been put in place for maintaining their stability are decommissioned for closure? With sufficient understanding gained during operations, it may be possible to adequately forecast behaviour and define a Design Acceptance Criteria appropriate for the slope, for post-closure, once operational controls are decommissioned. This paper is hoped will help address this dichotomy and provides suggestions to meet industry objectives. It is also intended to promote discussion on this transition, such that industry and regulator perspectives can be accommodated alongside each other within the forthcoming Large Open Pit (LOP) Guidelines for Mine Closure handbook publication, currently in preparation under the auspices of the LOP initiative.

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“…However, the same FoS does not mean the same for a given degree of uncertainty or level of reliability. In this regard, Macciotta et al (2020Macciotta et al ( , 2021Macciotta et al ( , 2022 identified that mature operating pits had been transitioning to performance-based designs, allowing operators to adopt lower DAC while ensuring adequate safety levels. Furthermore, it was identified that the target FoS-PoF pairs proposed in the 2009 DAC were inconsistent in terms of the statistical relationship between FoS-PoF.…”

Section: Introductionmentioning

confidence: 99%

Probabilistic pit slope stability analysis targeting a reliability-based design acceptance criteria: a parametric study

Velarde,

Macciotta

2023

SSIM 2023: Third International Slope Stability in Mining Conference

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Design of open pit slopes is a decision-making process which aims to maximise the ore recovery while minimising the excavation volumes. The current practice of designing open pit slopes adopts the widely accepted Guidelines for Open Pit Slope Design by Read & Stacey (2009). An optimum design should satisfy a design acceptance criteria (DAC). However, designing open pit slopes is a complex process that involves inherent risks and uncertainties. As a result, reliability analyses are becoming increasingly important for performance-based slope designs. In a reliability approach, the amount of information on the slope materials and behaviour would reflect the reliability of a slope design. This paper presents a parametric study defined by the uncertainties of the rock mass strength properties and the slope geometric configurations at three different design reliability levels targeting a reliability-based DAC (RBDAC). The reliability assessment is performed using probabilistic analysis adopting the two-dimensional limit equilibrium method and Monte Carlo simulations. The input variables for the rock mass strength are defined through probability density functions (PDF) that capture the natural variability, while the input variables of geological structures are defined through kinematic assessments.The PDFs of the rock mass strength properties were modelled based on the generalised Hoek-Brown criterion using the mean, coefficient of variation (COV) and dependence between quantitative properties of the criterion. Results show that most of the resultant pairs of Factor of Safety (FoS) and probability of failure and associated COV of the resulting FoS (COVFoS) are consistent with the RBDAC. Based on this, a redesign is proposed showing the applicability of the RBDAC and comparing it to the current DAC. This approach has significant implications for slope optimisation or mitigation plans for future pushbacks in case of instabilities.

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Design acceptance criteria for operating open-pit slopes: An update

Cited by 9 publications

References 24 publications

Critical challenges impacting the advancement of slope design reliability

Critical challenges impacting the advancement of slope design reliability

Transitioning from mine operations to closure: the dilemma of differing geotechnical design acceptance criteria perspectives

Probabilistic pit slope stability analysis targeting a reliability-based design acceptance criteria: a parametric study

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