Design acceptance criteria for operating open-pit slopes: An update (original) (raw)
Related papers
A risk consequence approach to open pit slope design
The Journal of the Southern African Institute of Mining and Metallurgy, 2006
Open pit slope design has conventionally been effected as a bottom up function utilizing available geotechnical information. This results in a decision criterion based on probability of failure and factor of Safety with a risk assessment being carried out on the proposed design slopes. The design approach recommended reverses the process using fault event tree decision methodology. The consequences of this approach are that acceptable risk criteria have to be determined by mine owners. Slopes are then designed by the technical staff to achieve these corporate goals. Benefits that arise from the process are that the owners take a proactive decision on the risk-benefit relationship allowing the technical staff to optimize the geotechnical exploration programme and design.
Pit Slope Configuration for Open Pit Mining – A Case Study
American journal of science, engineering and technology, 2024
To achieve stable pit wall slopes, it is imperative to obtain a fair knowledge of the rock mass characterisation before designing the pit. Insufficient knowledge of the competency of the country rock could lead to using unsupported slope configuration in the design process which can consequently lead to slope failure. In this study, the geomechnical properties of the Bremen-Nkosuo concession are analysed using Bieniawski's classification scheme to determine the Rock Mass Rating (RMR) for defining safe pit slope configuration of the Nkosuo pit. The findings show that the rockmass are best described as 'fair' for the two main lithologies existing at the concession. Subsequently, localised adjustment factors are applied to the calculated RMR to arrive at Mining Rock Mass Ratings (MRMR). These MRMR values are correlated with 50 m fixed stack height and 1.2 safety factor to determine optimum Bench Slack Angle (BSA) of 54° and 57° for host sedimentary and granitic rocks respectively. For individual benches, optimum slope design configurations were 10 m, 800, and 6.6 m respectively for bench height, bench face angle and catch berm for metasedimentary rocks. Likewise, that for granitic formation were 10 m bench height, 800 face angle and 6.0 m catch berm width. These configurations are in conformance with mineral and mining regulations of Ghana. Slope stability assessment was performed which included Slope Mass Rating (SMR), Kinematic and Limit equilibrium analysis. From the analysis, multi-bench scale slope instability occurrence was found to be rare but single-double scale could be possible at the western wall of the planned pit with probability of failure of about 0.4. Presplit and trim shots perimeter blasting techniques are recommended to maintain the integrity of the final pit walls at certain areas.
Critical challenges impacting the advancement of slope design reliability
SSIM 2023: Third International Slope Stability in Mining Conference
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.
Governing risk elements through open pit slope optimization
Journal of the Southern African Institute of Mining and Metallurgy, 2018
With the increasing competition in global mineral markets, designers are attempting to drive down overall mining costs. The demands for steeper pit slopes have triggered developments in the field of modern and comprehensive slope design. Risk-based optimization techniques are one of the most challenging state-of-the-art solutions for enhancing conventional procedures. Recognizing risk aspects has a fundamental role in updating the methods. Considering geotechnical and mine planning issues, this study describes the consequences of varying slope angles on final pit walls. Twenty-three risk elements are introduced and discussed in four groups: economic, technical, strategic, and regulatory compliance. Related examples are given on the state of the elements, and possible ways to achieve them from overall slope optimization studies of the Sungun copper mine in Iran. The circumstances indicate that decisions on optimized slopes do not relate only to geotechnical studies, but that relevant consequences depend on the four groups. Evaluation of the elements can promote slope optimization based on the concepts of risk. pit slope design, risk evaluation, slope stability, mine planning, Sungun copper mine.
Risk Assessment of Open Pit Slope Design at PT Adaro Indonesia
2014
Risk assessment of open pit slope stability is an important aspect to be considered in a decision making of slope design. The risk of slope failure that occurred on the slopes of the mine affect two factors namely the failure probability (FP), and consequences (C) of slope failure. FP is obtained from the collection of the value of Safety Factor (SF) < 1 compared to the total value of SF, while the consequences is estimated from the sectional area multiplied by the width of slope failure. Physical and mechanical properties of sandstone was collected from PT Adaro Indonesia, and tested by “Kolmogorov-Smirnov (K-S)” fitting method to obtain an assumed theoretical distribution that be sued with the character of the original distribution data. “Monte Carlo (MC)” and “Latin Hy- percube (LH)” sampling method is used as a tool to generate sample data, and both methods were compared. Finally Validation is conducted in order to propose an acceptable criteria of FP for single slope of sand...
Resilient Design of Large Open Pit Slopes
Although significant advances have been made in understanding the mechanics of pit slopes, numerical modelling hasn't significantly impacted on the reliability of the design process. It is well known that legacy modelling approaches don't simulate large slopes well. In recent times, the emergence of very large Finite Element (FE) models with more than ten million degrees of freedom and the ability to simulate a large number of discrete structures, has allowed a step change in the simulation precision for slopes. The model size allows global and local effects to be realistically simulated in one model for the first time and the process can be better integrated into normal open pit slope engineering processes. Some examples of simulation of very large open pits are shown that demonstrate the challenges and some recent advances in modeling large slope behavior. Significant limitations in the current measurement and observation regimes of open pits have been identified.
Inter-ramp and bench design of open-pit mines: the Portage pit case study
Canadian Geotechnical Journal, 2011
Using a case study, this paper presents an integrated methodology for assessing structural slope stability at the inter-ramp and bench levels. Robust algorithms have been developed and implemented to compute, at inter-ramp and bench levels, slope orientations and slope stability using input data compatible with a commercially available mine-design software tool database structure. Multi-criteria stability analyses were performed based on various design criteria. Susceptibility maps were produced enabling the identification of zones of concern in the designed pit. The obtained results suggest that inter-ramp angles do not present instability concerns over the entire pit surface. At bench levels, potential instability zones were identified within two structural domains totalling 6% of the total pit surface.
2020
A transparent, pragmatic geotechnical design system is outlined that presents a selection of risk options with associated risk/reward for decision makers. Risk options termed ‘robust’, ‘balanced’ and ‘aggressive’ have been defined appropriate to ‘critical infrastructure’, ‘typical industry’ and ‘low risk’ mining environments (where the safety risk and the consequences of failure on the budgeted mine plan are acceptably low), respectively. The geotechnical model includes ‘most realistic’ and ‘reasonable lower case’ conditions. A ‘realistic’ design principle requires reporting a Factor of Safety on the realistic case, rather than to reduce design inputs due to uncertainty. Uncertainty is transparently covered by the ‘lower case’ in sensitivity analyses. Indicative probabilities of failure are estimated and a simple empirical tool estimates the consequence of failure in terms of the area of mining floor impacted. These together with indicative value or tonnage estimates are presented t...
REM - International Engineering Journal
The traditionally and widely used Lerchs-Grossmann algorithm presents wellknown limitations that newer propositions attempt to overcome. The direct block schedule (DBS) methodology, which has gained relevance with computational advances, obtains the final pit as a natural result of production sequencing, different from Lerchs-Grossmann-based algorithms. This process flow applies constraints in the final pit definition stage attempting to provide a more realistic result and to minimize risks. Slope instability is a common and inherent risk to open pit mining and may affect the project's net present value (NPV). A study of the impacts of slope angle variations on safety indexes and final pit NPV provides an auxiliary tool for the overall slope angle definition process. This article presents a case study in which the effects of variations of the overall slope angle on the safety factor (SF) and project NPV were analyzed. A total of 25 pits were generated by each studied final pit definition methodology, and each pit had the sections with the varied slope angles analyzed in the stability assessment, resulting in a total of 150 slopes analyzed. A comparison between the results obtained by the two different methodologies implemented in commercial software is presented. The results show no relationship between the NPV and the overall slope angle using the DBS methodology. An analysis of the results for each geotechnical sector obtained by the traditional methodology was conducted and may contribute to the trade-off analysis between the best slope angle to achieve a reasonable SF and the maximum NPV.