Risk-Based Design and Management of Open Pit Slopes Workshop

15 May 2020 | Freshwater Bay Room, Hyatt Regency Hotel Perth | Western Australia

Within the mining community, geotechnical risk is often underappreciated, sometimes ignored and seldom properly quantified. In all areas of geomechanics, the uncertainty and variability that engineers need to deal with necessitate a rigorous process of quantification or, in the very least, robustly qualifying likelihoods and consequences. There appears also to be a large gap between the state-of-the-art and the state of general practice when it comes to the qualification and quantification of geotechnical risk. The aim of this workshop is to provide a forum to discuss the methods used to design for geotechnical risk and those used to manage these risks; to identify shortcomings; and to close the gap between the state-of-the-art and the state-of-practice.

 

Preliminary Programme

 

07:30REGISTRATION
08:20Welcome and introductionProfessor Phil Dight, Australian Centre for Geomechanics
08:30The future of risk-based design in the era of prescribed factors of safetyAdjunct Professor Tim Sullivan, Pells Sullivan Meynink
09:00Risk-based water management in open pit miningJon Hall, AQ2 Pty Ltd
09:30Failure investigations – where do you start?Emrich Hamman, AngloGold Ashanti Ltd
10:00Uncertainty, design reliability and slope riskMichael Dunn, Debswana
10:30Slope risk and collaborative decision-making under uncertaintyDr Stephan Arndt, Dassault Systèmes
11:00Risk identification and management in a large open pitDr Felicia Weir, Pells Sullivan Meynink
12:00LUNCH
13:00Practical considerations for applying and understanding risk-based designJulian Venter, AngloGold Ashanti Ltd
13:30Risk management: is it a number’s game, a process or judgement?Alex Duran, Pells Sullivan Meynink
14:00Accounting for sources of uncertainty in slope design: from theory to practiceArturo Maldonado, BHP
14:30AFTERNOON BREAK
15:00How to determine the minimal number of specimens required for laboratory testing of rock properties and support the classification of rock mass domainsDavid Gaudreau, Newmont Goldcorp
15:30Lower and upper bounds for slope stability analysis based on the Hoek-Brown criterionAssociate Professor Ali Karrech, The University of Western Australia
16:30WORKSHOP WRAP UP
 

 

Workshop Facilitator

Professor Phil Dight
Professor of Geotechnical Engineering
Australian Centre for Geomechanics
The University of Western Australia, Australia

Workshop Presenters

Michael Dunn
Debswana

Abstract title: Uncertainty, design reliability and slope risk 
Click to view the abstract summary

The relationship between geotechnical uncertainty and design reliability for open pit slopes will be will discussed and these will be linked to the impact they have on slope risk from safety and economic perspectives. Slope design acceptance criteria will be discussed in this context,  as they may not adequately relate to slope risk unless the geotechnical uncertainty and design reliability are understood. This leads to the use of risk-based design methods and this will be demonstrated using briefcases studies.

Michael has 25 years’ mining geotechnical engineering experience in operational, corporate and consulting roles. He has experience in South Africa, Australia, New Zealand, Indonesia, Ghana and the USA, covering a range of deep to near surface underground mining methods and small to large open pits. Michael has held several senior roles at AngloGold Ashanti, Newmont and SRK Consulting. In November 2015, he joined Evolution Mining as the Group Manager – Geotechnical and was responsible for providing geotechnical oversight and guidance for several underground and open pit operations and tailings storage facilities. Michael joins Debswana in 2020. Michael has a strong interest in the geotechnical design process, especially with respect to understanding geotechnical uncertainty and managing geotechnical risk. Michael is a Fellow and Chartered Professional of the AusIMM and has published 28 technical papers.

Alex Duran
Principal Geotechnical Engineer
Pells Sullivan Meynink

Abstract title: Risk Management – is it a numbers game, a process, or judgement
Click to view the abstract summary

The mining industry has a diversity of experience, views and approaches in managing risk at the operational level. The scope of risk mitigation at an operational level largely covers; personnel and equipment. A shift over the last decade has seen the emergence at a corporate level of “delivering value to shareholders” and role of “a better global citizen”. This shift has trickled down to operations such that risk mitigation has seen a change in approach coupled with embracing, the public, environment and perceived corporate image. The question this presenter poses is “risk management – is it a number’s game, a process or judgment?” This presentation focusing on the authors experience on how the risk mitigation process is addressed through different approaches, some of the shortcomings and learnings.

Alex is a principal with PSM. Alex has been actively engaged in providing geotechnical advice to the open cut mining industry for over 30 years and has worked on a diverse range of projects both within Australia and overseas. Within the last 10 years, focus has been on providing advice to the coal sector for both dragline and truck /shovel operations. Part of this experience has been with steeply dipping strata, uncommon to Australia, and has brought a raft of challenges in design the slopes and managing the risk.

David Gaudreau
Director Mining
Newmont Goldcorp

Abstract title: How to determine the minimal number of specimens required for laboratory testing of rock properties and support the classification of rock mass domains. Click to view the abstract summary

The workshop focuses on a procedure using statistical inference leading to the determination of practical laboratory strength, deformability and quality parameters obtained on rock specimens.

Upper or lower bounds of rock mass properties can be obtained following a methodology involving chosen confidence interval and precision index.

This enables planning of rock mass characterisation sampling for wall design as well as adjustments should the chosen sample size not fit the intended statistical confidence.

Course notes will be available and practical examples will be shown to demonstrate the approach.

David has over two decades of mining, geotechnical and mine production management experience. He serviced sites and projects in Australia, Canada, Indonesia, China, Laos and India. He was involved in several projects spanning diverse geographical areas for surface and underground operations, ranging from conceptual studies to mine closure planning and execution. David has had leadership roles in mine operations management, geotechnical engineering, technical services management as well as consulting. He joined Newmont in September 2017 as Director Mining for the Australian region.

Emrich Hamman
VP Geotechnical Engineering, Mining and Technical
AngloGold Ashanti Ltd

Abstract title: Failure investigations – where do you start?
Click to view the abstract summary

The aim of the presentation is to provide an overview on some of the assessments that will be completed during the investigation of a failure in an open pit.  These assessments requires the investigator to delve into a number of processes that are typically employed by an operation to manage the Ground Control hazard. In order to evaluate these processes, the investigator needs to understand the context within which these processes are defined, implemented and applied.  In this overview the main focus will be on geotechnical engineering processes and those immediate, external inputs that will impact it.

Emrich has been working as a geotechnical engineer in the mining industry since graduating as a civil engineer from the University of Stellenbosch in 1996. He’s career spans designing and implementing excavations in materials ranging from weathered and saturated surficial to ultra-deep highs stress underground environments.
He started work as a seismologist in the South African Deep Level mines, while working in the Savuka rock engineering department, assisting with what is still the world’s deepest shaft pillar extraction. The new millennium provided a change of scenery, when in 2000, Emrich started working on open pit mines in Tanzania and Namibia, before doing expat work for a couple of years in Mali (West Africa). He transferred to Australia in 2004, working on the Sunrise Dam Gold Mine open pit and the then underground feasibility project.
Since he has slowly moved away from the coal face into a more corporate role – first as the regional geotechnical engineer for AGA Australia, and then as a principal engineer in a corporate governance role for AGA. Currently he leads a team of principal geotechnical engineers in providing service and support to the International Operations of the AGA group.

Jon Hall
Consulting Hydrogeologist
AQ2 Pty Ltd

Abstract title: Risk-based water management in open pit mining
Click to view the abstract summary

Open pit water management takes many forms, ranging from low yield pit wall drainage to achieve reduced pore pressures, to groundwater interception or sump pumping to minimise wet pit floor conditions, up to diversion of surface runoff to prevent significant pit flooding. The drivers behind each are many and varied and each needs to be investigated when designing open pit mining and developing ongoing water management plans.

Jon is a hydrogeologist with over 30 years in local and international mine water management consulting experience. Much of this work has been associated with open pit and underground mine inflow control, and pit slope and underground pore pressure control. Over the last 15 years or so, he has been commissioned by many international mining companies to provide high level technical and due diligence reviews relating to mine dewatering and depressurisation.
Over his professional career he been a mine geologist and a hydrogeologist with the Geological Survey of WA before starting his consulting career with Australian Groundwater Consultants in 1983. He was a founding director of Aquaterra in 1998 and continued with the group as a Technical Director after it after became part of the RPS Group in 2010. He recently left RPS to join a number of his old Aquaterra work colleagues at AQ2, a specialist mine water management group.

Associate Professor Ali Karrech
Associate Professor and Graduate Reseach
The University of Western Australia

Abstract title: Lower and upper bounds for slope stability analysis based on the Hoek-Brown criterion Click to view the abstract summary

The stability of slopes in open pit mines is a major problem that challenges geotechnical engineers where optimum pit shapes are critical. The parameters that influence slope stability and the criteria of failure are fairly understood but over-conservative design approaches are often preferred, which can result in excessive overburden removal jeopardizing profitability. Numerical methods such as Finite Element and Discrete Element modeling are instrumental to identify specific zones of stability but they remain approximate and do not pinpoint the critical factors that influence stability without extensive parametric studies. The large number of degrees of freedom and input parameters may make the outcome of numerical modeling obsolete and subprime compared to analytical solutions.

In this paper, we propose a simple method of slope stability analysis based on the yield design theory and using the Hoek-Brown criterion. The yield design theory offers rigorous lower and upper bounds describing the behavior of slopes under specific loading conditions. The former condition derives from the compatibility of equilibrium and strength and the latter results from the application of the principle of virtual work. The proposed approach describes, for the first time, the stability of heterogeneous slopes using the yield design theory and Hoek-Brown criterion. The results are presented as rigorous mathematical expressions and in the form of stability charts involving the loading conditions and the rock mass properties emanating from the plasticity criterion.

The model is applied to an open pit mine located at Mt Isa (Queensland, Australia) where the rock formation includes eight geological units (including shale, siltstone, and volcanic strata) of various mechanical properties. Those geological units are interested with three sub-vertical faults. The data used for modeling have been extracted from published paper that investigated the stability using finite element modelling. This example showcases the applicability of the model for two mining stages of respective depths 77 and 180m.  

Ali has more than 15 years of research experience in materials and structures for resource engineering applications. His research interests include computational geo-mechanics, poromechanics, plasticity, damage mechanics, and multi-physics coupling. He has published about 100 peer refereed journal articles and book chapters and has contributed to over 50 national and international conferences. Ali worked for the Petroleum of Abu Dhabi (2007-2009), CSIRO-Earth Science and Resource Engineering (2009-2012), The University of Western Australia (since 2012)

Arturo Maldonado
Principal Geotechnical Engineer
BHP

Abstract title: Accounting for sources of uncertainty in slope design: from theory to practice
Click to view the abstract summary

This is an experience design-risk approach where slope design is focused to account for diverse sources of uncertainty like geology models, hydro models, strength properties and gradually explore in how all of that is translated into a design choice where a trade between risk and economics are further thought by risk-owner, design engineer and ground control owner in the way that optimal design is pushed forward.

Arturo has gained 18 years of experience applying geotechnical engineering within varying surface mining environments across several commodities (Copper, Nickel and Iron Ore). This also includes its application within both Along-Strike Shallow Open cuts (Iron Ore mines) and Deep Open pits (Antamina, Tintaya and Mt Keith mine sites). His experience spans all aspects of geotechnical work including the design of field investigations, standardisation of data collection, Life of asset slope design process development, setting up reconciliation requirements and standardisation of ground control practices. Arturo holds a MSc degree in Structural Geology from the University of Brasilia (Brazil), and has an Engineering degree, with Honours, in Geology (Peru). More recently, he is a part time student at the University of Western Australia and a PhD Candidate in Rock Mechanics through his research in the determination of bedding shear strength of shale materials in the Pilbara. Arturo is currently the Principal Geotechnical engineer at BHP in Western Australia Iron Ore, with previous exposure within the Glencore and Rio Tinto teams across his career.

 

Tim Sullivan
Principal, Pells Sullivan Meynink
Adjunct Professor, UNSW

Abstract title: The future of risk-based design in the era of prescribed factors of safety
Click to view the abstract summary

Since the inception of probabilistic approaches to slopes over four decades ago, risk-based design has been the gold standard for slope design. However, throughout that time even some of the most rigorous attempts have often failed to achieve the design aims. In parallel some regulatory authorities have attempted to mandate rigorous design standards. There has been a further change more recently where many of the larger mining companies have prescribed minimum design standards. These approaches are all concerned with controlling risk, but how successful are they? This presentation examines many of the contributing factors underlying actual performance and critically evaluates the main stumbling blocks to achieving better outcomes. The aim is to attempt to reconcile the future of risk based designs in the era of prescribed factors of safety.

Tim has more than 40 years experience in large open pit design. Tim worked with Coffey for 18 years before establishing his own firm in 1993. He is a Fellow of both the Institute of Engineers and the Australian Institution of Mining and Metallurgy and is currently Adjunct Professor of Geotechnical Engineering at UNSW. Tim has worked throughout Australia, Asia-Pacific, Africa and Central America; notable appointments include Coroner’s Advisor on the Thredbo landslide. Tim was a Mining Warden by the Victorian Government for the Yallourn Inquiry.

Julian Venter
Manager Geotechnical Engineering
AngloGold Ashanti

Abstract title: Practical Considerations for Applying and Understanding Risk Based Design Click to view the abstract summary

This presentation provides practical guidance on applying risk based design. The presentation starts with a practical useable definition of probability that is not contained in most engineering textbooks, but borrowed from Economics. This definition helps the user to understand what probabilities mean and how to evaluate them. The definition is demonstrated through a practical example. Guidance is then provided on selecting probabilistic parameters for analysis using the Principle of Maximum Entropy through a practical example.  The presentation concludes with a section on practical decision making using probabilistic concepts.

Julian Venter graduated from the University of Pretoria (UP) in 2000 with a Bachelor’s degree in Civil Engineering. Subsequently he obtained Master’s degrees in Geotechnical Engineering from UP in 2004, a Graduate Diploma in Rock Mechanics from the University of the Witwatersrand in 2007 followed by an MBa and a Master’s degree in Mineral Economics from Curtin University in 2017. He started his working career with SRK Consulting in Johannesburg in 2002 where he gained a well-rounded geotechnical exposure to a variety of problems including open pit and underground mining and construction. For geotechnical risk work carried out at SRK he was co-recipient of the SAIMM Gold medal in 2007 and also co-recipient of the ARMA Award for Applied Rock Mechanics Research in 2009. In 2008 Julian and his family moved to Tom Price in Australia where he joined Rio Tinto’s Tom Price Iron Ore mine as Senior Geotechnical Engineer accountable for Tom Price and periodically Marandoo and Brockman 2 operations. After carrying out further roles in Rio Tinto in Mine Planning, Technical Services Superintendent at Tom Price, Technical Serves Superintendent at Brockman 2 and Geotechnical Superintendent for the East Pilbara, he left Rio Tinto in 2015 to join SRG Limited as National Manager Geotechnical Engineering. In 2016 Julian started with AngloGold Ashanti as Geotechnical Manager for the Continental Africa Region. A position he still holds. Throughout his career Julian has served on open pit design teams in roles including: contributor, technical lead, project manager, project director and third party reviewer for more than 200 open pits and cut backs. Based on this experience he has become a champion of rigorous data based design processes based on a proper understanding of risk.

Dr Felicia Weir
Principal
Pells Sullivan Meynink

Abstract title: Risk identification and management in a large open pit
Click to view the abstract summary

Risk identification and management is critical for the successful operation of open pit slopes. This presentation looks at the identification and risk management of two different large-scale slope instabilities at a case study site. This site also utilizes numerous large “failing” waste dumps, which are a significant source of risk. The presentation looks at how these waste dumps are managed, through operational techniques and monitoring, including the use of drones.

Felicia Weir is a Principal Engineering Geologist of Pells Sullivan Meynink Pty Ltd, with over 12 years’ experience in her field. Felicia joined PSM after completing her PhD in Geomorphology. Felicia’s primary areas of practice include engineering geology, 3D geotechnical models and stability assessments for open cut mining.
Felicia enjoys a spectrum of projects from short life operations to large scale pits in complex risk settings. The development of accurate ground models and appropriate slope designs is her greatest pleasure. With recent work as Acting Geotechnical Superintendent at Ok Tedi Mine she has a good appreciation of the challenges faced in operations.
Felicia has worked on numerous major mining projects across Australia, Asia and Africa, including a number of large and technically challenging projects including Olympic Dam Open Pit Expansion, Ok Tedi operations and design in geothermal conditions at Lihir Gold Mine.

Dr Stephan Arndt
Portfolio Senior Technical Manager
Dassault Systèmes GEOVIA

Abstract title: Slope risk and collaborative decision-making under uncertainty
Click to view the abstract summary

The importance of geotechnical risks and risk-based design for slope stability has been well established in the industry. Still, there remain large gaps between expert analyses and the technically possible and acceptance criteria at different stages of a project from study to implementation and production. With the industry moving to more integration and automation the need for quantitative tools and better understanding of the geotechnical reality of a mine is fast becoming a bottleneck.

Stephan has over 25 years’ experience in advanced simulation methods in applications of rock mechanics, seismicity, discrete fracture networks, coupled multi-physics simulations, fracture mechanics and constitutive models. His interests include emerging technologies in Geomechanics; cross-industry synergies; scalability of modelling methods; integration of machine learning and optimisation; better quantification of risk under uncertainty; and using high performance computing, visualisation and virtual reality in decision making. Stephan has extensive consulting experience in the mining sector consulting for major mining projects in Australia and overseas.