Geotechnical Risk Management

To reduce business and safety risk at Anglo American, it is imperative that mine waste dumps and stockpiles are strategically managed to ensure all design objectives are met. These objectives must be aligned to deliver value through integrated, risk-and opportunities-based closure planning and execution, to establish safe, stable, and non-polluting post-mining landscapes that leave a positive and sustainable legacy for stakeholders. A structured approach according to engineering design principles is suggested for the design and implementation of these facilities. Key characterisation and design aspects are discussed including hazard classification and risk assessment. The risk management process is subsequently applied to ensure adequate controls (risk based) are put in place during the design phase and that said controls are effective during operations. The process is supported by a global information management system aligned with FutureSmart Mining™, Anglo American's innovation-led pathway to sustainable mining: technology, digitalisation and sustainability working hand in hand. It leverages innovative and sustainable methods to drive safe, responsible production with high performance teams.

Recently, the mining sector in Brazil and worldwide is facing challenges to advance on digital transformation and industry 4.0 , in general, focused on Risk Management of Geotechnical Mining Structures (pits, dams, dumps, tunnels and other retaining structures). These challenges are bottlenecks to the achievement of the main goal of promoting operational efficiency needed for a predictive management system and, consequently, delivering safer mining to society. Key bottlenecks include: superficial risk assessment with ineffective controls; poorly defined processes with ineffective data entry and delivery; superficial indicators (data), lack of data engineering concepts; many manual inputs throughout the process, culminating in many error inputs and inefficiency; data dispersion across multiple systems and databases; and, ultimately and most important, the inefficient, untraceable risk information and communication flows at all levels of corporate governance. The aim of this work is to present a methodology and case study applied to deal with these In order to promote an efficient usage of the tools, the strategical objectives of geotechnical monitoring must be defined, including Geotechnical risk management, failure mechanisms and monitoring strategy, instruments specifications, reference levels and data integration. Furthermore, Geotechnical data analytics must be addressed, including correlation and sensitivity, trends, forecasting and visual interface dashboards and communications. So that, the entire risk process is covered, since risk assessments methodologies up to governance criteria, exposing the importance of each step of building a reliable risk management, prior to selecting and implementing digital transformation measures. Finally, a roadmap is presented, empowering the concept of continuous improvement for the achievement of promoting the operational efficiency essential for a predictive management system and, consequently, delivering safer mining to society.

The Ground Control Plan (GCP) for geotechnical structures comprises a management program to address potential damage related to Fall of Ground (F.o.G.) events in a mining complex. Usually, the GCP covers only structures located inside the mining lease, such as open pits, mining waste dumps, underground excavations, and others. However, in many cases, geohazards related to linear transport infrastructures, can represent some of the most critical risk scenarios to the business, including safety, environmental, social, legal, and material consequences. In this context, The Minas-Rio Slurry Pipeline, belonging to Anglo American Iron Ore Brazil (IOB), is the longest ore slurry pipeline in the world, and transports iron ore mined at the Serra do Sapo Mine up to The Açu Port, comprising 528,00 km. Throughout its course, the pipeline Right of Way (RoW) servitude, covers more than 30 municipalities, with diverse geological-geotechnical, environmental, social and economic contexts. The aim of the paper is to present the GCP in such context, covering the identification of exposure to geohazards, governance best practices and continues improvement, inherently embedded in the GCP process. Additionally, tools and processes enabling effective risk management are discussed, including Failure Mode Effect Analysis (FMEA), Event and Fault Tree Analysis (ETA & FTA), as well as Bow Tie-and Baseline risk assessment. The main failure mechanisms posing a risk to the pipeline, include landslides, rock falls, debris flows and tunnels / retaining structures anomalies. Based on these assessments, processes for the development and review of reliable geotechnical designs, the clear definition of roles and responsibilities, are defined before effective procedures are put in place. Finally, a well-defined strategy in terms of monitoring, emergency plans, risk reduction plans and audits, are essential for both mitigatory and preventive controls to ensure effective geotechnical risk management.

Summary paper discussing the necessity of 3D analysis in open pit, rock slope, stability analysis.

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.

Fall of Ground management at Venetia is through Anglo American Plc slope safety critical controls. Each critical control has defined key performance indicators and standardised number metrics that are monitored and reported on. Through application of the hierarchy of controls, rockfall risk management is addressed in several elements of the slope safety critical controls. This case study defines the design acceptance criteria for the rockfall retention metric and the minimum required effective bench width to satisfy the design acceptance criteria determined through calibrated rockfall analysis. Demonstrated in the paper is a documented approach for evaluating and reporting on effectiveness of design objectives linked to a Trigger Action Response Plan to intervene where objectives are not achieved and/or runout exceeds the controls. This approach provides a basis to objectively measure and report to management on compliance to a key safety critical control and its effectiveness.

Venetia Open Pit Mine, after 30 years of production, will be transitioning to underground production in Q4 2022. This presents an interesting conundrum: aggressively maximise pit ore recovery and short-term revenue or follow a more conservative, high reliability slope design and defer ore to later underground recovery. Preferences are weighted towards high reliability plans with limited 'surprises', as there exists limited stockpile contingency options if unplanned slope failure occurs. Ore delays cannot be afforded. An inter-ramp scale slope failure, 130 m high and 85 m wide, occurred on the south wall of Venetia Diamond Mine in July 2020. The failure impacted the principal haulage ramp to the orebody as well as a substantial resource of high-grade ore. Back analyses were subsequently completed to verify failure mechanisms as well as refine foliation shear strength contributing to slope failure. The results of the back analyses were then used to determine an acceptable mine plan for recovering the ore below the failed section of slope, without compromising further slope instability and minimising deferred ore volumes. The back analyses process applied three-dimensional limit equilibrium slope stability models to replicate the behavior of a strong, but highly anisotropic rock mass and cross-cutting geological features that contributed to the failure. Once a calibrated model was developed a series of pore pressure scenarios were applied to a suite of final pit slope designs at incremental face angles (with veracious pore pressure scenarios) for bench-by-bench progression to ultimate pit geometry. These model scenarios provided the mining operation to follow quantitative risk-based decisions as ground conditions and slope performance unfolded in real time mining. This paper outlines the back analysis, model calibration and forward planning post slope failure. The risk management and mining processes used to successfully mine the remaining ore from open pit methods is also documented.

Slope failures are an inevitable and often an economically attractive aspect of pit slope design in the mining industry. Industry design standards typically accept up to 30% of benches in surface mines to collapse, provided that they are managed so that no personnel are at risk. Too many failures impact on productivity, and larger scale failures are less tolerable due to their economic impacts to mine schedules and negative publicity, irrespective of how well they were managed. The ability to monitor and predict slope failures in surface mines is paramount for safe design execution. In the 2020's high frequency, near real-time surface deformation monitoring systems include ground-based synthetic and real aperture radars, prisms, GNSS points and extensometers. An array of subsurface monitoring is also available, some of which is also high frequency. Each monitoring system needs to be calibrated to local ground conditions and climates to serve as an effective early-detection device for predicting 'as small as possible' sized fall of ground events with sufficient warning to enable the removal of personnel, and where practicable, mining equipment prior to collapse. This paper discusses the Slope Monitoring and Response protocols developed for Moore and Monte Negro large open pits at Pueblo Viejo gold mine in the Dominican Republic, and how they are integrated with mining practices to significantly improve safety and minimize operational delays. These pits are unique since ground conditions vary, such that both brittle and ductile ground behavior occur on various scales.

Slope failures are an inevitable aspect of economic pit slope design and execution in the mining industry. Industry standards typically accept up to 30% of benches in surface mines to collapse, provided that they are managed such that no personnel or critical infrastructure are at risk. For larger scale instability, the acceptable limits reduce to 5-10% and 3-5% for inter-ramp and overall pit slopes. Ground control measures in large surface mines typically include real time monitoring systems and comprehensive response protocols to prevent personnel and equipment being exposed to safety risks associated with slope failures. Economic risks are often managed with attempts to reduce slope design uncertainty with ongoing site investigations including drilling, mapping, photogrammetry and also the use of monitoring data. Our ability to collect and manage various forms of data is increasing rapidly, although our ability to critically analyze all of this data and its potential significance to slope stability is not (yet) increasing at the same rate. This paper investigates the Cumba slope failure, a 70 meter high non-daylighting planar rock slide, which occurred in the Dominican Republic in 2019. The investigation and technical review utilizes and integrates all available data to improve the geotechnical model, inclusive of key geological inputs, major structure, rock mass constitutive models and groundwater. Data from aerial photogrammetry and ground-based synthetic aperture radar data are used in conjunction with three-dimensional limit equilibrium analysis techniques to develop realistic simulations of ground behavior that are qualitatively and semi-quantitatively. Three-dimensional analysis results are compared with two-dimensional cross-sectional analyses. With the strategic combination of available information, it was possible complete this technical review in less than one week, and demonstrates the benefits of technology integration in geotechnics.

Slope stability modeling techniques and deformation monitoring technology has significantly improved in the last decades. Three-dimensional modelling is rapidly becoming standard practice for the design and optimization of open pit mines and waste rock dumps. This paper presents a case study demonstrating the use of 3D limit equilibrium analysis for predicting stockpile failure mechanisms and stability for the construction of Hondo waste rock stockpile in the Dominican Republic. Slope stability analysis results are used to facilitate a risk appraisal to provide guidance for mine planning and stockpile optimization.

Slope stability modelling by practicing geotechnical engineers has mostly been limited to 2D cross-sections. Faster computers and improved user interfaces of 3D software are now facilitating the routine application of 3D limit equilibrium and finite element analysis for slopes in complex ground conditions. Deformation monitoring technology has rapidly developed with real-time interferometric radar now capable of providing updates every minute across an entire slope. This is a step-change in risk management compared with manual surveying of prisms going back as little as 10-15 years. Radars are geo-referenced to the same coordinate system used in stability models. This paper presents a case study to illustrate the effectiveness of integration and interoperability between 3D stability models with interferometric radar data for understanding ground behaviour and managing landslide risk.

Resumo: O presente estudo apresenta a implementação de um sistema de monitoramento geotécnico nos cinco túneis pelos quais passam o mineroduto do sistema Minas Rio, propriedade da Anglo American, por meio da utilização de instrumentação discreta e contínua. Com o objetivo principal de ter um controle geomecânico dos túneis e visando garantir seu objetivo de transporte, optou-se em utilizar a convergenciometria e medidores de trincas (crackmeters) como ferramentas de monitoramento. Neste contexto, este trabalho irá apresentar as diretrizes e definições necessárias ao monitoramento, a metodologia aplicada e as etapas para realização deste serviço, como a definição dos locais de monitoramento, a instalação do sistema em campo e os procedimentos para coleta de dados. Concluída a etapa de implementação do sistema, foi realizada a etapa em que os instrumentos foram acompanhados por um período (operação assistida), garantindo os padrões de qualidade da instrumentação. Correções de leituras e revisão de dados plotados mostram que a tecnologia de medição proposta é um sistema simples e objetivo para aquisição de dados, se mostrando confiável para medições de convergência de túneis e adequado para o processo de monitoramento de juntas e fissuras nas estruturas estudadas. 1 INTRODUÇÃO Mesmo que os empreendimentos hoje contem com uma excelente investigação geológica e geotécnica do terreno e já na parte do projeto são apresentados diversos estudos prévios de campo e laboratório, tais como os mapeamentos geológicos, sondagens e ensaios geofísicos e geotécnicos, a engenharia de escavações subterrâneas tem um grande desafio a frente, uma vez que o comportamento do terreno pelo qual avança a escavação contém incertezas. Neste cenário, para reduzir a imprevisibilidade do comportamento do maciço rochoso, procura-se estudar a resposta do terreno frente à escavação e para isso, faz-se uso da instrumentação geomecânica.

Interferometric synthetic aperture radar (InSAR) application has recently benefited from an increased number of service providers (with more diverse satellite constellations), advances in algorithm processing methods and, with reductions in costs, is becoming a widely accepted method of surface deformation monitoring in the mining industry. InSAR monitoring is consequently being applied to a wide array of mine infrastructure and geotechnical risk management scenarios ranging from construction to operating and closed mines, including natural slopes traversed by mine access roads, rail and pipelines, to engineered open pits, waste dumps and tailings dams, as well as identification of subsidence and onset of potential collapse due to either active or legacy underground mining and/or karstic terrain sinkhole development. With this increased interest from a growing array of diverse technical disciplines, it has been shown that InSAR monitoring is complex and there are many variables to consider and levels of monitoring possible. Furthermore, making sense of vendors’ claims on system deliverables versus demonstrated outcomes can be challenging. These aspects need to be considered and aligned with the anticipated mode of instability, size, magnitude and rate of movement, and the business risk. Using a premium InSAR product (as high resolution data with two look directions and high frequency reports) when budget is not a limiting factor or using a budget constrained product (such as low resolution freely available Sentinel data), unless appropriately matched to the business risk profile (and deformation characteristics), will likely lead to underwhelming and possibly misleading results. This paper describes how decision trees were developed to assist in selecting the level of InSAR monitoring considering the asset infrastructure risk and the physical characteristics of the area of interest. The decision trees were built such that the user, without extensive technical knowledge of how InSAR functions, can make an independent evaluation of what InSAR product is adequate. A simple cost versus risk trade-off tool is discussed, outlining how the decision trees were developed to determine whether InSAR would be a viable solution at the site and what the appropriate resolution, acquisition frequency, report frequency, and orbit/s should be. This provides a consistent framework for firstly evaluating and matching monitoring rigour with geotechnical risk, secondly a process to facilitate alignment and ideally optimisation of monitoring outcomes between disciplines, and finally for communicating these to management to demonstrate an effective business case for monitoring. Keywords: InSAR, slope stability, tailings dams, displacement monitoring, risk management, decision tree

The challenges of representing geotechnical failure mechanisms in software is being gradually addressed as search algorithms and computing power advance, especially to deal with complex anisotropic rock masses in which failure mechanisms are commonly three-dimensional (3D). This paper presents a case study of an iron ore mine with highly anisotropic rock mass strength that has been back-analysed using 3D limit equilibrium analysis methods. In order to provide as realistic model inputs as possible, field characterisation data and the reconstruction of the failed surface were used, as well as the material properties available from laboratory tests or bibliographic references. A probabilistic approach was applied to the initial parameters, resulting in a series of stochastic simulations that provided scenarios for the failure moment, when the Factor of Safety achieved close to 1.0. Then, based on the knowledge of the local geological-geotechnical context and failure mechanisms, a range of values for the geomechanical parameters were achieved to enhance the constitutive model of the rock mass.

Closure planning is a fundamental requirement for all existing and planned future mines. However, there are no accepted industry guidelines for how to assess options for open pit closure or for advancement of the closure plan in parallel stages with overall project development and operation. Ideally, closure planning needs to consider the site setting, develop the “big-picture” strategy, and work downward from there; balancing the objectives of the operator, regulator and community. At present, too much inappropriate detail is being included in “early-stage” closure plans that, when approved, become committed. This paper outlines the “State-of-Practice” geotechnical and hydrogeological guidelines for closure planning and implementation being developed by the Large Open Pit (LOP) project research group. The new guidelines are intended for use by geotechnical and hydrogeological mining professionals addressing closure design criteria, risk management, detailed planning and implementation. Benchmarks are provided for stakeholders, including regulators and the community, to judge whether adequate investigations and planning have been completed for appropriate stages of overall project development. Three case studies are provided to illustrate how changes of closure approach produced a substantially better outcome.

The ability to monitor and predict slope failures in a surface mining setting is paramount for safely executing economically feasible open pit slope designs. Ground-based monitoring systems have proven to be effective for decades; however, with the geographical extensive nature of some mineral deposits, multiple open pit mining operations typically incur additional challenges of deploying and maintaining ground-based systems (compared with a single, large open pit). Monitoring strategies in the 2020s have significant opportunity to integrate satellite based InSAR (interferometric synthetic aperture radar) as part of the control measures depending on the expected failure mechanisms and risk profile. This paper uses case studies to explore the practical application of InSAR to ‘unveil unknowns’ for multiple open pit mining operations where ground monitoring capacity was previously constrained. Case studies include the retrospective analysis of historic slope failures, improving understanding of existing geotechnical hazards and improving engineering geological and slope stability models based on real slope performance data.

The Ground Control Plan (GCP) for Minas-Rio System is a process to address risks related to Fall of Ground (F.o.G.) events along the complex, including Open Pits, Waste Dumps, Slurry Pipeline and Industrial Assets. As per preconized by the Anglo American (AA) Group Technical Standard AA TS 401 001, the content includes processes maps, roles and responsibilities, risk management, design processes, operational water management, procedures, hazard identification and mitigations, monitoring system, data collection, functional trainings, emergency plans, learn from incidents and risk reduction plans. Besides, the document's content is in line with Brazilian National Mining Agency (ANM) resolutions as well as best practices from regulatory guidelines worldwide.

Slope stability modeling techniques and deformation monitoring technology has significantly improved in the last decades. Integration between modelling and monitoring is becoming seamless enabling practicing geotechnical engineers to validate their stability models with actual slope performance data. This paper presents a case study demonstrating the use of aerial photogrammetric settlement analysis, satellite and ground-based radar data from a ductile slope failure mechanism on an overburden stockpile to validate a geotechnical model applied in 3D limit equilibrium analysis. Following the calibration of 3D models, stockpile design options are reviewed to minimize instability risks to ensure safety and protect the mine plan.

Assessing geotechnical stability in rock masses is challenging using 2D analysis methods when the failure mechanisms are driven by 3D geometry and anisotropy. For such cases, it is necessary to use 3D analysis to correctly assess slope stability in such environments. This work aims at presenting a methodology and a case study in Serra do Sapo soft iron ore deposit using 3D Limit Equilibrium method. The paper will examine 3D implicit geological models with anisotropic rock masses. To capture the failure mechanism correctly, the work identified the main structural drivers, such as structural geological contacts and internal features or "lenses" such as filonites. Finally, the authors compared 3D limit equilibrium results to 2D limit equilibrium out�comes. The comparison showed that 3D analysis provided a reliable way to predict instabilities due to 3D interactions.

Rock slope failure has the potential to cause multiple fatalities in open pit coal, iron ore, base and precious metals mining operations. Rigorous geotechnical design, inspection and monitoring are critical to preventing and managing slope failure. The risk of slope failure should initially be engineered to a tolerable level during the design process considering the economic impacts of an event on the operation. Should instability then be observed during or post excavation, the risk to operations must be quantified so appropriate control measures can be implemented to manage residual risk. This risk to operations can be quantified using numerical analysis or empirical relationships. This paper presents new empirical relationships for estimating the volume and runout distance of an open pit slope failure using slope geometry as a predictor. The aim is to provide practicing geotechnical engineers and engineering geologists a starting point for selecting appropriate stand-off distances or exclusion zones until additional control measures, such as slope remediation, can be implemented. Case studies are sourced from a range of slope geometries (up to 800 m overall height) and commodities (coal, iron ore, copper, gold, boron).

RESUMO: Atualmente, a maior parte dos estudos de estabilidade de escavações subterrâneas são compostos por análises do comportamento elasto-plástico dos maciços rochosos, e/ou análise cinemática das possíveis cunhas e blocos formados na parede da escavação, sendo que as duas análises são feitas separadamente. Este trabalho apresenta uma metodologia de estudos de estabilidade de escavações subterrâneas projetadas em meios descontínuos, por meio de testemunhos de sondagem, ensaios de laboratório e dados levantados in-situ. A metodologia tem como foco o estudo de estabilidade em galerias, realces de lavra ou quaisquer outros tipos de escavações subterrânea feita em meios descontínuos, onde os eventos de rupturas ocasionados pela presença de descontinuidades geológicas são comuns. A primeira etapa da metodologia consiste no levantamento das orientações espaciais, através de camadas guia, ou seja, descontinuidades cujas a direção de mergulho e inclinação são conhecidas e pouco variáveis. Essa técnica de obtenção aproximada das orientações espaciais é denominada "semi-orientação". Em seguida, são obtidas as características geotécnicas das descontinuidades, por correlação com o grau de rugosidade, além da natureza e grau de alteração do material de preenchimento das mesmas. A partir daí, são elaborados os modelos geológico-geotécnicos com a determinação das famílias de descontinuidade e suas respectivas resistências. Os estudos de estabilidade são feitos por meio de análises cinemáticas de cunhas e análises por elementos finitos com a discretização das descontinuidades e, posteriormente, sugerido um sistema de contenção adequado. 1. INTRODUÇÃO Os estudos de estabilidade em escavações subterrâneas são feitos, em sua maioria, por meio de métodos numéricos que consideram os maciços rochosos como meios contínuos, como o método dos elementos finitos, e/ou utilizando métodos de análises cinemáticas de cunhas. Basicamente, os métodos numéricos utilizam os parâmetros geotécnicos elásticos e plásticos do material, sendo que os meios descontínuos (com presença de fraturas, acamamentos e falhas geológicas) são comumente correlacionados a meios contínuos, através de parâmetros geotécnicos equivalentes. Já as análises cinemáticas de cunhas avaliam o equilíbrio das cunhas e blocos formados pela interseção descontinuidades nas paredes das escavações, com base nos parâmetros de resistência das famílias de fraturas, acamamentos ou falhas presentes. Os dois métodos possuem limitações intrínsecas às suas concepções. As análises numéricas, por meios contínuos, não conseguem reproduzir o comportamento mecânico das descontinuidades presentes no maciço rochoso, enquanto que, nas análises cinemáticas, somente os blocos e cunhas superficiais, nas paredes da escavação, são avaliadas. Ao longo da última década, muito tem se evoluído no sentido de criar códigos com conceitos mistos, para que seja possível reproduzir um cenário mais próximo da realidade, onde o comportamento geotécnico de rocha e das descontinuidades sejam avaliados ao mesmo tempo. A obtenção das orientações espaciais de descontinuidade a longo prazo, ou seja, em fase de pesquisa, quando ainda não existem escavações abertas na área de interesse, pode ser custosa e muitas vezes difícil de se adaptar a uma rotina de mina em operação. Este trabalho apresenta uma metodologia para modelamento geológico-geotécnico de maciços rochosos descontínuos, a partir de testemunhos de sondagem "semi-orientados", ou seja, por meio de camadas-guia, culminando em estudos de estabilidade em meios dessa natureza.

Purpose: promotion of the operational efficiency necessary for a predictive Risk Management system and, consequently, deliver a safer mining to society - Digital Transformation Process is a key issue; • Bottlenecks: Basic challenges of the Mining Sector to advance in digital transformation process: - Shallow risks analysis with ineffective controls; - Poorly defined processes, with ineffective data entries and deliverables; - Un-switched indicators (data) - the absence of data engineering concepts; - Many manual entries throughout the process, culminating in many error entries and inefficiency in the use of labor force; - Inefficient, non-traceable risk information and communication flows at all levels of corporate governance.

This paper discusses the engineering, hydrogeology, operational practices and TARPs that facilitated deeper mining and goodbye cuts at the De Beers Canada Victor Diamond Mine. A number of technical challenges related to water management and adverse geology late in the mine life were overcome in order to successfully meet and exceed the planned mining depth. Extensive pit dewatering and a pit water management program were implemented not only to maintain dry working conditions for operations but to ensure highwall stability and reduce the formation of hazardous ice columns along the highwalls. After a 15 m tall ice column failure, bench design was optimised to ensure perched aquifers occurred as low on the highwall as possible. Where the uppermost ice columns formed, strategic reinforced meshing was installed to eliminate the possibility of sudden ice column failures that could not be predicted with the monitoring systems in use. Excellent limits blasting outcomes and better than expected conformance to design also allowed for inter-ramp limestone slope optimisation. Additionally, a 'ploughing' style failure mode was of concern due to blocky limestone underlain by saturated clays and mudstones. Here, a pit redesign and highwall depressurisation thresholds were used to prevent this failure mechanism from occurring, as well as developing vibrating wire piezometer trigger action plans. The overall results of the integrated hydrogeological and geotechnical designs and slope management practices were positive and contributed significantly to slope design optimisation and safely recovering additional ore. What worked technically and in terms of people and procedure are shared.

The De Beers Canada Victor Diamond Mine is located in the James Bay lowlands of Northern Ontario. This case study presents the evaluation of geotechnical stability and pit lake filling. The work was used to support decisions that informed risk assessments and the closure plan for two key phases: 1. Active closure, with personnel undertaking rehabilitation activities in and surrounding the pit. 2. Post-closure, when personnel and equipment have been demobilised from the mine site. Risk-based monitoring plans were developed along with Trigger Action Response Plans (TARPs) to ensure that closure of the pit proceeds safely and efficiently while satisfying regulatory requirements. Active mining operations in the open pit ceased in mid-2019 and pit filling is underway. The pit required the installation of a major dewatering system, with up to 94,000 m 3 /day, pumped mostly from dewatering wells. Considerations for closure included the site remoteness, safety, global and local stability, water quality of the pit lake, permitting commitments, and closure regulations in the province of Ontario. A major consideration was the rate of pit filling. Rapid pit lake filling using water from the nearby Attawapiskat River leads to more favourable stability and environmental outcomes. A simple hydrogeological model was used to predict the filling rate and the final pit lake level for a number of potential closure options. This was used to schedule a phased geotechnical monitoring approach to ensure the safety of the operators as the pit walls became increasingly pressurised. A trade-off study has informed the preferred approach for pit lake development. Active pit closure has recently been completed and closure reclamation is ongoing.

Currently, most studies on stability of underground excavations include two separate analyses: the elastoplastic behavior of rock masses and/or kinematic analysis of possible wedges and blocks formed in the excavation walls. This paper presents a case study carried out at the Vazante Zinc Mine in Minas Gerais, Brazil, where studies on stability of underground excavations in discontinuous media included survey reports, laboratory tests and in-situ collected data. In this context, where galleries and mining stopes are excavated in discontinuous media, collapse events caused by the presence of discontinuities are common. First, the spatial orientation, geometric arrangement and mechanical characteristics of the discontinuities intercepted by the core samples were collected. The spatial orientation was based on guide layers, which are discontinuities with known dip direction and variable and dip. The geotechnical characteristics of the discontinuities were obtained by correlation with the roughness degree and the nature and weathering degree of the filling material. From there, the geological-geotechnical models were developed, which were the basis for the finite element analysis in discontinuous media of the designed excavations in the sections 13225 and 13300, between levels 210 and 345 of the mine. For comparison and complementation, wedge kinematic analysis and finite element analysis in equivalent continuous media were performed and, later, an arrangement for the reinforcement system was suggested. The results of these studies show that, in general, continuous models tend to be more conservative and have wider deformation zones, while discontinuous models are able to show in more detail where the displacements occur, and how the families of discontinuities affect the stability of excavations. © 2018, Associacao Brasileira de Mecanica dos Solos. All rights reserved.

Historically, the mining sector in Brazil and worldwide is one of the last to implement innovative processes and technologies in its operations. In the current Brazilian context, due to the catastrophes that have occurred in recent years, Risk Management of Geotechnical Mining Structures (pits, dams, piles, tunnels and other retaining structures) faces some basic challenges to advance on digital transformation process. These challenges are bottlenecks to the achievement of the main goal of promoting operational efficiency needed for a predictive management system and, consequently, delivering safer mining to society. Key bottlenecks include: superficial risk assessment with ineffective controls; poorly defined processes with ineffective data entry and delivery; superficial indicators (data), lack of data engineering concepts; many manual inputs throughout the process, culminating in many error inputs and inefficiency; and, ultimately and most important, inefficient, untraceable risk information and communication flows at all levels of corporate governance. The objective of this work is to present a methodology and case study applied to deal with these specific challenges in Risk Management of Geotechnical Mining Structures, using techniques already established in other sectors, as well as new technologies available and viable in the market. Specific objectives include: efficient risk analysis methodologies and practices for the identification and implementation of efficient controls; methodologies and practices for mapping effective processes; use of data engineering techniques for switching and correlation of indicators; elimination or reduction to acceptable levels of manual inputs throughout the process to promote team efficiency and optimization and, finally, use of applied technologies (software, sensors and equipment) that allow the systematization of data acquisition, correlation and interpretation, workflows and predictive and online risk indicator updating.

Commercial 3D limit equilibrium and 3D finite element analysis software has been available to geotechnical engineers for nearly a decade. Current 3D modelling software allows the direct importation of as-built designs to back-analyse slope stability. The same 3D modelling software allows the direct importation of deformation data recorded by slope stability radars. This interoperability between modelling software and monitoring data provides geotechnical engineers an invaluable method to back-analyse material properties and refine slope stability models. This paper presents a case study showing the integration of 3D limit equilibrium, 3D finite element and synthetic aperture radar monitoring data to determine suitable remediation actions to stabilise an identified deforming section of slope in an open cut gold mine.

Papua New Guinea (PNG) is host to several topographically, geologically and climatically different environments. The central and western provinces of the mainland (‘the highlands’) are topographically elevated between 1,000 and 4,000 m above sea level. The terrain is very rugged and the climate is cool all year round. This region is hosted by uplifted sea floor sedimentary rocks, some of which have been metamorphosed. There is no wet or monsoon season. Rather, rainfall occurs quite steadily all year round. Annual rainfall can easily exceed 10,000 mm in some areas and low magnitude earthquakes are frequently experienced. The smaller outer islands are topographically flatter, seismically active and receive in the order of 5,000 mm annual rainfall. Rainfall usually occurs in the form of high intensity thunderstorms. The climate is very hot and humid. These islands often comprise a combination of volcanics and some sedimentary rocks. Mining is a major industry in PNG and very large open pits have been constructed with excavated slope heights ranging from 300 to 1,000 m. Open pit mine slopes are designed with a serviceable life of no more than 10 to 20 years. As such, predicted and well-managed failures or landslides are usually considered acceptable. Waste rock and low-grade ore are often placed in constructed rockfill dumps and stockpiles which range in heights from 50 to over 300 m. High rockfill slope heights developed on often steep foundations, coupled with the erosive and pore pressure effects of rainfall and seismicity can create significant landslide hazards. This paper presents the cumulative efforts of practitioners managing risks associated with rockfill dumps and stockpiles in PNG.

The observation of an existing structure supporting a particular maximal load provides a direct constraint on the possible range of values its resistance capacity may take. The implied update of structural reliability allows monitoring and maintenance planning to be done from a risk optimal perspective. Existing proof load-based reliability updating techniques require multiple numerical computations which are often too cumbersome for routine use. By building on the assumptions of the first order reliability method, this study develops and validates a first order reliability updating approach which is computationally efficient. The resulting formulation is shown to be applicable to reliability problems tractably considered using the first order reliability method. This method is illustrated for two example structures: a reinforced concrete beam forming part of a highway bridge to which traffic loading data is applied, and a granular embankment forming a seawall on a shoreline mining operation for which the phreatic surface level is monitored.

Newcrest Mining Limited open pit operations at Telfer (Western Australia) have excavated steep slopes. Current and future planned mine designs also intend to implement steep slopes in order to maintain profitable ore to waste strip ratios. When not adequately considered in the design process, rock falls can present a significant hazard in open pit mines. The management of rock fall hazards becomes particularly vital for steep slopes. Numerical models are often used to assess the effectiveness of benched slope designs or rock fall barriers to minimise risk to personnel or equipment. Commonly used numerical modelling software and simulation impact theories include: • ‘RocFall’ — two-dimensional lumped-mass impact model (2DLM). • ‘Trajec3D’ — three-dimensional rigid body impact model (3DRB). Numerical models use coefficients of restitution to characterise the amount of energy lost due to the inelastic deformation during the collision of a rock with the slope or bench. The input parameters are vastly different for 2DLM and 3DRB and they are seldom calibrated with any site-specific rock fall case studies or field test data during project feasibility studies, and often remain uncalibrated through the operating life of the mine. In order to best manage rock fall hazards for steep slopes through design, a series of rock fall trajectory field tests were carried out to facilitate the development of calibrated 2DLM and 3DRB numerical models. The calibrated models were then utilised to assess the effectiveness of various slope design geometries. The influence of model selection was found to have a significant impact upon the results. This paper compares rock fall trajectory predictions obtained from calibrated 2DLM and 3DRB models for steep slope designs in hard rock.

Papua New Guinea (PNG) is host to rugged terrain with high rainfall and seismic activity. This combination of environmental and climatic factors results in a high frequency of landslide activity in both in-situ, natural slopes, excavated mine pit slopes and even more so, in rock fill dumps and stockpiles. This paper presents the cumulative efforts of practitioners managing and operating high risk rock fill dumps and stockpiles in PNG.

Working stress design (WSD) has long been used in geotechnical practice. However, in the past decade this has, to a significant extent, been replaced by limit state design (LSD) which is the basis for Eurocode 7, and presents a more robust approach in dealing with uncertainties. Factually, however, none of these approaches quantify the degree of uncertainty in design parameters or their cross correlation; aspects which directly affect the reliability of a design, especially geotechnical designs since soil is amongst the most variable of engineering materials. This paper introduces underlying concepts for the response surface - first-order reliability method (RS-FORM) and provides a demonstration of how this reliability technique can be implemented to analyse the stability of homogeneous slopes in practice.

For the last 20+ years, slope stability modelling by practicing engineers and basic software users has mostly been limited to 2D cross-sections. Faster computers and improvements in the user interface of 3D software are now facilitating a shift towards the routine use of 3D stability modelling. Deformation monitoring technology has also been rapidly improving, with real-time interferometric radar now capable of providing updates every minute across an entire slope. This is a step-change in risk management compared with manual surveying of individual survey prisms going back as little as 15 years. Radars are also geo-referenced to the same coordinate system used in slope stability models. This paper presents case studies to illustrate the benefits of routinely adopting 3D modelling for slope stability as well as the added advantage of integrating the 3D models with interferometric radar data, thereby bringing together predictive models and live monitoring data.

De Beers is currently developing closure plans for two open pit mines. At first glance they appear quite similar; both are relatively remote, have operated for 10 years, have similar pit dimensions (250-300 m deep and 1.5 km wide) and have Palaeozoic sedimentary host lithologies with weak upper units overlying more competent lower materials. However, Victor Mine in the sub-Arctic Canada, is one of De Beers wettest mines (dewatering volume of 75,000 m 3 /d) and is hosted predominantly in good quality limestone with excellent final wall performance. While Voorspoed Mine, in semi-arid Southern Africa required virtually no dewatering, has poor wall performance associated many with mudstone and country rock breccia instabilities. Victor Mine is expected to achieve stable pit lake in less than 10 years (and less than 2 years with supplementation from a nearby river), while Voorspoed will take over 100 years to reach ultimate pit lake level (due to low groundwater inflows, high evaporation and limited opportunity for flow supplementation). This paper describes a process to determine closure stability design acceptance criteria (DAC) and characterise the zone of long-term surface disturbance surrounding the pit (i.e.: potentially unstable pit edge zone to define the closure exclusion zone). This involved: 1) Pit break back-analysis using i) industry guidelines; ii) an empirical approach based on historical slope instabilities; and iii) stability analysis using predicted post-closure phreatic surfaces. 2) Estimates of erosion potential. These results along with the well documented historical slope performance provided the basis for detailed Geotechnical Risk Assessments which addressed two periods. • Active closure with personnel undertaking rehabilitation activities in and surrounding the pits, and • Long-term closure, personnel and equipment not permitted within the long-term break back zone. Risk-based monitoring plans were developed along with Trigger Action Response Plans (TARPs) to ensure that closure of the pit proceeds safely and efficiently while satisfying the regulatory requirements.

The geometry and structural history of high-grade granite-gneiss units, which host the Venetia diatremes in South Africa, have been modelled in 3D using an implicit, rules-based, conditional geometrical technique. The volume contains a pervasive, dominant foliation, which forms the main plane of strength anisotropy in ongoing design and mining of the Venetia pit, which has a planned final depth of approximately 465 m below surface. The well-developed S 2 foliation is a continuous feature that was locally re-oriented during D 3 and D 4 and localised ‘wrapping’ around competent amphibolite/hornblendite lenses or boudins. These local variations have important implications for pit design and operational risk management, particularly where they dip adversely out of the slope, or occur at the base of bench stacks, or in inter-ramp areas. These structures, when undercut by dips steeper than their friction angle, may result in planar sliding, presenting an operational safety risk. Best practice requires early identification of these occurrences, to make design adjustments where warranted. Lithological contacts, which have been transposed into parallelism with the S 2 foliation, and a robust set of structural data collected over the last 10 years, are analysed to quantify and represent the variable orientation of S 2 in 3D space. This contribution describes several methods, using leading software packages such as Leapfrog Geo™, Micromine™ and Python, to generate representative S 2 form surfaces and anisotropy block models, both of which are used for downstream geotechnical engineering analysis. Outputs are also translated into apparent dip “heat” maps that show the angular interaction between S 2 foliation and a pit design surface. These methods augment, and lessen the dependence on, typical 2D wedge-shaped design sectors that are commonly employed in pit design. This approach has important safety and economic benefits. As the rock mass fabric is characterised, it supports quick identification of potentially higher-risk areas (e.g. adverse undercut fabric with greater likelihood of slope instability) in current mine plans, which justifies more detailed analysis and/or additional monitoring controls to ensure safe and efficient mining. It also allows rapid mine design optimisation.

Historic underground workings can be a source of unexpected collapse or subsidence of ground when being mined via open pit methods presenting a safety risk to personnel and an economic risk to achieving planned reserves or disruption to the mine plan. Processes for managing these risks in active open pit operations have been developed in many mine sites around the world, however an engineering and monitoring solution for bridging underground workings below permanent haulage ramps in open pit operations has not been well established. The gold mine in this case study has been mined using both underground and open pit mining methods since its commencement in the 1970's. The current active open pit excavates through extensive historic underground workings. Recently a design constraint was implemented to avoid placing haulage ramps above historic underground working without an engineering and monitoring solution in place. This constraint limited the potential extraction of the mine resource. Several methods were investigated to either engineer out the exposure or change the failure mechanism from brittle to ductile and thus allow for deformation monitoring as a means of risk mitigation. The options selected involved a woven geotextile in combination with RSSI SMART markers as an innovative solution to this unique risk. The paper discusses the investigation, implementation and ongoing performance of the geotextile and SMART marker system.

Landslide monitoring and management is a challenging task in the remote, rugged and sparsely-populated Ok Tedi Mine area of Papua New Guinea (PNG). Ground elevations are 500–2200 m above sea level. Annual rainfall is 8000–13000 mm. Earthquakes may exceed magnitude 7 on the Richter scale; but are commonly 3–6. Avalanche debris from an ancient landslide dating back to 6700 BC underlies much of the existing terrain. Recent landslides often involve reactivation of old debris materials. The stability situation is compounded by local inhabitants’ deforestation of rugged hillsides to establish gardens. Limitations of various monitoring systems are discussed and case studies presented.

Since the turn of the century, advances in the computing, information technology and telecommunication sectors have empowered geotechnical engineers to collate vast and large amounts of data on a daily basis. More recently, with instability in commodity prices, most mining companies have been reluctant to proportionally increase staffing levels. Effectively and logically storing this wide array of data, and moreover, enabling the validation, analysis and subsequent presentation of the data are paramount in an ever faster paced mining environment where we aim to proactively manage emerging risks and uncertainty. Geotechnical databases for open pit and underground mining operations have been created on a combination of the acQuire Geoscientific Information Management System and Navstar Geoexplorer. The purpose of these systems is to establish and maintain a central source of data that is easily collected, entered, analyzed, visualized or exported by relevant stakeholders. This paper presents an overview of the system capability and flexibility to meet geotechnical engineers ‘requirements at unique and complex mining operations. Through system upgrades and the training of personnel, the output from geotechnical sections has markedly increased while staffing levels have remained relatively constant over last three years.

Underground mining in gold, base metals and coal deposits has occurred for centuries, and even millennia in some parts of the world. The mechanization of mining and economic appeal of open pit mining in the last 30 years has facilitated the conversion of many historic underground mines into large open pits. Historic underground workings or voids below the working floor of an open pit and voids behind or intersected by pit slopes have the potential to collapse and induce uncontrolled ground movement which may cause harm to personnel or equipment as well as impact upon the economic profitability of the operation. Identification and demarcation of controlled exclusion zones from potential voids beneath the working floor is common practice to prevent personnel and equipment entering at-risk areas. However, the way these potential void risk areas are determined and managed vary significantly from operation to operation. Risk management strategies for working in close proximity to historic underground workings are dependent on several factors including ground conditions, historic underground mining method and size of voids (open or filled stopes, room and pillar, caving, horizontal and vertical developments) and void status (open or filled, surveyed or estimated size). Blasting to collapse void areas and controlled excavation practice are paramount for safe mining. This paper discusses various approaches of managing risk in open pits with historic underground workings below from gold and base metals deposits in Australia and Africa.

The Telfer underground sub-level cave (SLC) operations are located approximately 600 to 1000 m below the west wall of Main Dome open pit at the Telfer Gold Mine, Australia. The Telfer SLC commenced caving in 2006 and broke through to the surface in 2009 forming a large subsidence zone that has progressively developed above the SLC operation. Surface deformations within the subsidence zone continue at a rate of 500 mm to 2000 mm per month and are dependent to the rate of underground mining in the SLC operation. Underground and open pit operations have continued concurrently with the progressive enlargement of the SLC subsidence zone. The stage 4 open pit orebody was solely accessible via the West Ramp, which is located adjacent to the SLC subsidence zone with notable steady state ductile deformation occurring on ramp. Risks were managed by understanding the cave propagation mechanism through modelling and monitoring, and the use of comprehensive TARPs (trigger-action-response-plans) and an array of real-time surface and sub-surface deformation monitoring instruments. This paper discusses the monitoring systems used to track the cave subsidence and monitor ground deformation. These include slope stability radar, automatic total stations with survey prisms, shape-accel arrays, time-domain reflectometers, seismicity monitoring arrays, networked SMART markers, surface extensometers, automated crackmeters and monthly aerial surveys. These monitoring systems were used to determine the cave subsidence zone shape, location, rate of propagation and the direct response in the slopes adjacent to the West Ramp. The monitoring systems and TARPs are critical for identifying approaching hazards and taking proactive risk mitigation measures.

Ok Tedi Copper-Gold mine is a large open pit mine in the Western Province of Papua New Guinea that typically receives in excess of 10,000mm annual rainfall. Surface water runoff generated during high intensity rain events initiates localized erosion on benches and bench faces on a daily basis. In regions of friable and highly fractured rock, the erosion rapidly undercuts geological structures; enabling larger instabilities to occur. When uncontrolled, the problem progressively worsens leading to the development of large chasms along major geological structures on pit slopes. Chasms up to 450m high and 250m wide have developed at Ok Tedi. Over the last decade, several remedial projects involving improving surface water management, slope depressurisation and targeted ground support campaigns have been undertaken to reduce chasm enlargements. During the progressive enlargement of these chasms, landslides and slope instabilities involving several hundred-thousand tonnes of debris are initiated and sent towards the mining area below. Slope deformation monitoring systems and geotechnical hazard awareness measures are used to manage the risk to personnel and equipment operating in the pit. These comprise two separate near real-time slope stability radar (SSR) systems, survey prisms monitored with automatic total stations (ATS), tension crack extensometers and visual inspections where practicable. Deformation threshold alarms for SSR and ATS, trigger-action-response-plans and 24-hour geotechnical engineer presence are utilized to monitor slope deformation, predict instability and provide a safe operating environment.

https://www.ausimmbulletin.com/feature/erosion-driven-slope-instabilities/

Ok Tedi Copper-Gold Mine is a large open pit mine in the Western Province of Papua New Guinea that typically receives in excess of 10m annual rainfall. Surface water runoff during high intensity rain events initiates localized erosion on benches and bench faces on nearly a daily basis. In zones of friable and highly fractured rock, the erosion quickly proceeds to the undercutting geological structures; enabling small-scale block toppling as well as planar and wedge sliding mechanisms to occur. When uncontrolled, the problem progressively worsens leading to the development of large chasms along major geological structures on pit slopes. Chasms of up to 180m high and 220m wide have developed at Ok Tedi as illustrated in Figure 1. With high inter-ramp slopes and the progressive loss of bench containment capacity, the chasms forming on pit slopes present a number of short-term risks to the operation including rock falls, debris flows and temporary loss of access to the ore body. Continued growth of the chasms has also had the potential to erode across and permanently destroy main haul roads. Effectively managing surface water runoff has been the most successful method of preventing the development of chasms. However, in some areas this has either not been possible or the rock was so friable that it had a limited success. As a result, numerous ground support methods including mesh & shotcrete, grouted piles, gabion baskets and lined drainage systems have been trialed in critical areas to reduce chasm enlargement. Safety is being managed through the use of real time slope monitoring systems including automatic total stations and slope stability radar.

A planar failure of approximately 600 kT occurred on the north wall of Centre Pit North (CEPN) at West Angelas Mine site in February 2010. The failure impacted a substantial resource of high grade iron ore and left a number of significant geotechnical hazards on and adjacent to the failure surface. These presented a series of challenges which had to be overcome in order to remediate the failure and reclaim the bulk of the buried ore. A number of recovery options were investigated and presented to management. This paper outlines the plan which was adopted, the challenges encountered during its implementation and the risk management and mining procedures used to bring the remediation and recovery to a successful conclusion.

Geotechnical design is characterised by a relatively large number of uncertainties, even if industry best practice is followed during the design process. Regulatory and corporate standards require appropriate geotechnical design and slope management. Rio Tinto Iron Ore (RTIO) have addressed this challenge by developing a geotechnical reconciliation process carried out during mine implementation. Design assumptions are verified and actual slope performance assessed to close the design cycle. Typically, geotechnical reconciliation includes checking design assumptions and implementation recommendations by mapping pit walls in addition to monitoring actual slope performance. RTIO Western Australia, has over 260 individual open pits at 13 operations across the Pilbara. As such, it is impractical to physically map geotechnical and geological parameters on all slopes. Instead, a risk based approach is taken to focus efforts on high risk slopes whilst still checking lower risk slopes for unforeseen hazards. In order to assess geotechnical risk, RTIO has developed risk assessment tools specifically tailored to support the practical slope management of multiple operations. The geotechnical reconciliation process has been successfully implemented in RTIO pits and is fundamental to effective geotechnical slope management. Improved verification of design assumptions has allowed for re-assessment of the pit design and improved hazard management in high risk pits. Two case histories are presented that illustrate the benefits of early identification of changes in actual conditions; one positive (better than expected) and one negative (poorer than expected) both leading to improved outcomes in terms of safety, design reliability and protection of the business plan.

Ongoing weathering of high rock slopes overlooking the DeCew Falls Generating Station No. 2 Powerhouse and transformer yard pose a risk to personnel and infrastructure. Originally designed and constructed as an unsupported cut slope more than 60 years ago, continued exposure to the elements has resulted in loosening, ravelling and undercutting of the slope and a steadily increasing frequency of rockfalls. As part of Ontario Power Generation's (OPG) long term vision for this plant, a permanent low maintenance rockfall mitigation programme was required. RÉSUMÉ La dégradation continuelle du haut talus en roc surplombant la centrale génératrice de DeCew Falls (station no. 2) et la cours de transformation adjacente pose un risque au personnel et aux infrastructures. Conçu et construite il y a plus de 60 ans comme pente sans support, l'exposition aux éléments a résulté en une dégradation de la surface du roc et un accroissement continuel de la fréquence d'éboulements rocheux. Un élément de la vision à long terme d'Ontario Power Generation (OPG) pour ces installations a été de commander un programme de réfection et de stabilisation permanente à faible entretien du talus de roc.

SYNOPSIS Namdeb's Southern Coastal mining operation is located in Southern Namibia, just north of the Orange River mouth. Diamonds were fi rst discovered in the area in 1928 and mining of diamondiferous onshore raised beaches has been the mainstay of Namdeb's production for nearly 90 years. The onshore beaches are now largely mined out but mining operations have systematically followed the ore zones westward, from land-based reserves into the sea. To access diamondiferous ore up to 30 m below sea level a beach reclamation process, called beach accretion, has been developed. Accretion advances the coastline westward and enables dry overburden stripping to bedrock using conventional load and haul fl eet. The mining operation is protected from the Atlantic Ocean by a western wall comprising in situ marine sands, overlain by recently dumped accreted beach material, and fi nally a 7m high constructed sand seawall. Namdeb's Southern Coastal Mine has been mining successfully below sea level for more than two decades , providing extensive empirical support for the sea wall slope design. However, as the mine moves westward, becoming progressively deeper, the limits of precedent experience are challenged and previous assumptions of homogeneous in situ materials are no longer appropriate. This paper describes the operational procedures and systems adopted to ensure safe and economic mining, as well as outlining the current empirical designs.

Rio Tinto's Western Australian expansion, combined with mining within structurally complex geology and increasingly below the water table, presents challenges in effective slope management to ensure safe and economic mining. The Geotechnical Management System (GMS) was developed by Rio Tinto Iron Ore (RTIO) to manage geotechnical risks identified during the design process and implementation, and to ensure feedback based on the 'as-found' conditions. The GMS utilizes a risk-based approach to geotechnical risk management and is centred on the geotechnical risk and hazard assessment management system (GRAHAMS). GRAHAMS is used to assess pre- And post-control risk for future potential risks (planned slopes), current risks (as-built slopes), and actual geotechnical hazards (realized risks) identified in the pit. This serves as a core operational risk management tool in identifying and prioritizing key risk sectors and management of critical controls. The system's database reporting functionality supports effective communication of operational risks to operational personnel, as well as reporting the risk profile across operations to management. A rigorous engagement process between design engineers and sitebased engineers is implemented to ensure that key design assumptions, limitations, risks, and opportunities are understood by the site teams. This information, together with mine plan schedule details, is used to assess the design risk and develop appropriate controls. These controls typically include slope performance monitoring and slope reconciliation. The design feedback loop is closed through sharing of key slope performance and reconciliation data with the design teams. The GMS has been successfully implemented in RTIO pits and is fundamental to successful geotechnical slope management. Improved characterization of design assumptions has allowed for re-assessment of the pit design and improved hazard management in high-risk pits. The GMS, GRAHAMS, and other processes reduce the incidence of unexpected slope instability. Improved understanding of rock mass conditions has allowed for economic optimization through redesign of slopes, allowing for an improved understanding of risk and fewer unexpected conditions (surprises), hence an increased realized value. © The Southern African Institute of Mining and Metallurgy, 2016.