Keynote Speakers

Christian Cancino
Geomechanics Engineer
Itasca Consulting Group Inc., USA

Christian is a mining engineer with experience performing slope stability analyses with traditional constitutive models as well as strain softening models and time-dependent behaviour. He has been involved with some of the largest open pit and caving operations and projects in the world. He has consulting experience on geotechnical aspects of the mining industry, including strain-softening and creep mechanisms, and has worked on open pit and underground metalliferous mining problems in Chile, Peru, Brazil, Argentina, Botswana, South Africa, Canada and the United States.

Presentation title: Numerical assessment of an overall instability at Bajo de la Alumbrera mine

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In May of 2017, an instability at overall scale occurred in the southwestern wall at Bajo de la Alumbrera mine. A cessation of mining followed due to unstable material reaching the pushback planned to mine the ore located at the bottom of the open pit. This paper describes the numerical modelling analyses developed to back-analyse the instability and to study the options to continue mining the remaining ore at the bottom of the open pit. In 2012, Itasca carried out a predictive analysis using numerical modelling (3DEC), suggesting that a large-scale instability was possible in the area. A new numerical model was developed in 2017 to back-analyse the instability in terms of Factor of Safety (FS) contours, achieving a good match with field observations. To continue mining the pushback below while meeting the acceptance criterion of the slope design, defined by a FS ≥ 1.2 at inter-ramp scale, sequential excavations were simulated from top to bottom. The model showed that an excavation 204 m high would be required to meet the acceptance criterion to resume mining in Pushback 12.

 

Dr Will Darlington
Principal Geotechnical Engineer
Grange Resources

Presentation title: Novel techniques for rockfall management using remote equipment at Savage River Mine

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Rockfall is a hazard in open pit mines with the potential to cause significant consequences. In December 2020, a rockfall event occurred at the Savage River Mine in Tasmania. In this event a 765-tonne block detached from the highwall, and rocks subsequently landed onto an active work area 210 m below.

Post-event investigations indicated that several additional controls were required prior to the resumption of mining in the area.  These included the installation of a rock fence, shear pins and a revised monitoring strategy to facilitate continued safe mining operations. However, installation of the rock fence and shear pins by traditional construction methods would expose personnel to an unacceptably high rockfall risk. Mitigation of this risk therefore required innovative techniques.

These included pre-fabrication of a sea-container fence and installation by use of remotely operated machinery. The shear pins were also installed using a remote drill rig, a remote excavator with a custom attachment and grouting by use of a long reach boom pump, thereby eliminating the previously required presence of exposed personnel in the elevated risk area.

This paper describes the construction and remote installation of the rock fence and shear pins.

Ian de Bruyn
Principal Consultant (Geotechnical Engineering)
SRK Consulting

Ian has 21 years’ experience in the fields of engineering geology and geotechnical engineering in both the mining and civil sectors. He has strong expertise in geotechnical assessment and provision of design parameters for open pit mining operations and has worked on projects involving large pits in challenging rock mass and hydrogeological conditions. He is well versed in rock mass characterisation and domain modelling for input into fragmentation analysis, selection of mining method and support design for underground mines. Ian’s projects have involved site investigation, characterisation, analysis, evaluation, design, risk assessment and reporting at all levels – from conceptual through pre-feasibility, feasibility and working design.

Keynote title: Building useful geotechnical models

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The success of any geotechnical design is dependent on the geotechnical model used in the design assessments. No matter the methodology adopted, the budget allocated, or the expertise assembled for the design analyses, an unsuitable geotechnical model will result in a sub-optimal outcome or misleading results.  The nature of any geotechnical model must be dependent on the type, amount, and spatial distribution of the information available and the purpose for which the model is constructed.  A geotechnical model for an open pit must allow for the generation of slope design parameters that are most appropriate for the geotechnical environment, taking into account the dominant mode(s) of failure, the level of confidence in the data and acceptable levels of risk. It may require a significant amount of evaluation, interpretation, and judgement to develop a model that is fit-for-purpose, even for one that appears simple. It is better for it to be approximately “right” than precisely “wrong”!

This paper discusses the conception and development of appropriate geotechnical models for slope design. It considers the types of information available, the level of study, the shape of the excavation, controlling failure mechanisms and uncertainties. It discusses how a model can be spatially defined and how the data can be best used to characterise each zone.  The lithology, alteration, structural and hydrogeology models that contribute to the geotechnical model, and the likely slope failure mechanisms, are important in selecting appropriate software or analysis methods that should be employed for slope design analyses. In this context, typical pitfalls in geotechnical models are examined.

Dr John Read
Independent Consultant
John R Read Associates Pty Ltd

Dr Read is a geological engineer with over 45 years’ civil and mining engineering project experience as a practitioner, consultant and mining research manager in a number of locations around the world, including Australia, Indonesia, Papua New Guinea, Fiji, USA, Canada, Brazil, Chile, Argentina, South Africa, and Zambia.

His particular expertise is in slope stability and since 1980 he has been specifically concerned with the stability of rock slopes in large open pit mines. In 1994 he was appointed deputy chief of the CSIRO Division of Exploration & Mining and executive manager of the Queensland Centre for Advanced Technologies, Brisbane. However, in 2004 he stepped back from both of these positions to first establish and then manage CSIRO’s industry funded Large Open Pit (LOP) project. The principal objective of the project is to perform research that improves our current methods of predicting the stability of rock slopes in open pit mines. Dr Read retired from CSIRO and leadership of the LOP project in 2014 but continues working with the mining industry as an independent consultant.

Presentation title: 3D limit equilibrium slope stability analyses, method and design acceptance criteria uncertainties

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A review of the information available in the public domain has shown that there are geological and mathematical uncertainties in the method used and the design acceptance criteria for 3D limiting equilibrium stability analyses offered to prepare slope designs in asymmetrical, closely jointed and interbedded and folded rocks. The geological and mathematical criteria assumed are concluded to be impracticable and not well enough understood with respect to the slope configurations that they are being applied. It is recommended that a geotechnical research project be undertaken to resolve these issues and uncertainties.

Rob Thomas
Principal Consultant
Absolute Geotechnics Pty Ltd

Rob’s career in mining began in a Brazilian gold mine in 2005 before a period in civil geotechnics in the UK. Since moving to Australia in 2008, Rob has been immersed in the engineering geology and geotechnics of WA’s resource sector, working in a range of site and office-based roles. Rob lead the mining geotechnics team of an international consultancy before founding Absolute Geotechnics in early 2016. Rob continues to provide geotechnical and engineering geological services globally across a wide range of commodities.

Keynote title: Visualising bias of structural orientation data

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Structural discontinuities represent an essential component of the geotechnical model for rock slope design. The bias associated with structural orientation data collected from different sources is reviewed, and existing methods of understanding and overcoming this bias are discussed. An alternative method of visualising the bias is presented. This method can be applied to single drillholes, datasets derived from multiple drillholes and scanlines, face mapping or combinations of multiple sources (e.g. a combination of drillholes and mapping data). The method provides a graphical presentation of the structural orientation bias within the selected dataset. The visualisation allows identification of areas of the stereonet in which discontinuities may be under-represented and enables consideration of potential methods to reduce the associated bias. The technique assists the geotechnical designer in understanding whether datasets selected for geotechnical analysis are representative and provides an opportunity to account for the bias.