Empirical Runout Prediction for Open Pit Slope Failures

John Whittall, Erik Eberhardt, Oldrich Hungr, Derek Kinakin

In the proceedings of: GeoRegina 2014: 67th Canadian Geotechnical Conference

Session: Mining Geotechnics

ABSTRACT: Runout Prediction for Open Pit Slope Failures John Whittall, Erik Eberhardt, Oldrich Hungr Geological Engineering - Department of Earth, Ocean & Atmospheric Sciences, University of British University of British Columbia, Vancouver, BC, Canada Derek Kinakin BGC Engineering Inc., Kamloops, British Columbia, Canada ABSTRACT Predicting the travel path and zone of influence of an open pit slope failure is a key tool in a mine's hazard assessment. Empirical runout prediction methods established for natural landslides have not yet been validated for open pit slopes. This paper compares the results of established runout prediction models for natural landslides to a dataset of 40 rapid open pit slope failures. Like natural landslides, the mobility of open pit slope failures increases with failure volume. Volume to angle of reach and volume to planimetric deposit area relationships show a promising correlation for open pit failures. Together these empirical relations could be used to predict the debris runout zone of influence and can be integrated into the mine hazard management plan. RÉSUMÉ Prédire le parcours de mouvement et la zone d'influence d'un glissement dans une mine à ciel ouvert est un outil essentiel pour l'évaluation des aléas associés avec l'opération d'une mine. Les méthodes de prédiction de parcours empirique, établies pour les glissements de terrain naturels n'ont pas encore été validés pour les pentes de mines à ciel ouvert. Cet article compare les résultats des modèles de prédiction de parcours établis pour des glissements de terrain naturels à un ensemble de données de 40 glissements rapide dans des mines à ciel ouvert. Comme pour les glissements de terrain naturels, la mobilité des glissements dans les mines à ciel ouvert augmente avec le volume de la rupture. Les relations entre l'angle de parcours et volume et entre la surface de dépôt planimétrique et le volume démontrent une corrélation prometteuse pour les glissements dans les mines à ciel ouvert. Ces relations empiriques peuvent être utilisées en tandem pour prédire la zone d'influence de parcours des débris et peuvent être intégrées dans le plan de gestion des risques associés avec l'opération d'une mine. 1 INTRODUCTION Recent experiences and consequences resulting from large open pit slope failures have increased regulatory and industry interest in the prediction of the corresponding runout and areas affected. A common approach to assessing the hazard posed by rockslide runouts involves the use of empirical models (Scheidegger, 1973; Li, 1983; Cannon, 1993; Corominas, 1996; Iverson, 1997; Fannin and Wise, 2001). The utility of these methods has been recognized for open pit failures (Rose, 2011) however they were developed solely based on natural rock slope failures and have not been validated for open pit slopes. Empirical models are amenable to slope hazard assessments and decision making in an operating open pit mine. Safety and economic constraints related to personnel, equipment withdrawal, and lost production leave little time for detailed deterministic analyses. Important site specific influences may be neglected or treated holistically, but at the same time geological uncertainty limits the degree of precision that can be expected. Empirical methods are quick, repeatable, and useful for bracketing site conditions where detailed data is limited. This paper qualitatively compares a dataset of 40 open pit slope failures with established empirical methods for landslide runout prediction. A variety of slope failure modes, rock types, slope geometries, and debris volumes are included in the dataset. Differences between open pit and natural slope runouts are discussed to highlight possible limitations to the applications of these empirical runout models in open pit mining. 2 DATASET The dataset of failed open pit slopes presented here was compiled using public domain sources. Various failure modes, rock types, and wall configurations are represented. If unspecified, volume estimates are assumed to be in-place. For consistency, where references provide both in-place and bulked volumes, the failure is plotted as its in-place volume. Primary references are included in Table 1. Where possible additional geometric estimates were taken from satellite imagery. 2.1 Types of Open Pit Slope Failures Case histories included in this assessment are pit wall instabilities that failed with a runout component. Primarily these failures were rapid, 'catastrophic', movements that meet Hungr et al.'s (2013) description of a rock avalanche. One case slumped with toe runout (case 14; see Table 1). Low energy and small volume (<100,000 m3) failures retained by effective slope hazard management measures (e.g., Highland Valley Copper, Sons of Gwalia, Lake Asbestos, Cadia Hill) were excluded from the dataset.

RÉSUMÉ: ical Runout Prediction for Open Pit Slope Failures John Whittall, Erik Eberhardt, Oldrich Hungr Geological Engineering - Department of Earth, Ocean & Atmospheric Sciences, University of British University of British Columbia, Vancouver, BC, Canada Derek Kinakin BGC Engineering Inc., Kamloops, British Columbia, Canada ABSTRACT Predicting the travel path and zone of influence of an open pit slope failure is a key tool in a mine's hazard assessment. Empirical runout prediction methods established for natural landslides have not yet been validated for open pit slopes. This paper compares the results of established runout prediction models for natural landslides to a dataset of 40 rapid open pit slope failures. Like natural landslides, the mobility of open pit slope failures increases with failure volume. Volume to angle of reach and volume to planimetric deposit area relationships show a promising correlation for open pit failures. Together these empirical relations could be used to predict the debris runout zone of influence and can be integrated into the mine hazard management plan. RÉSUMÉ

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Cite this article:
John Whittall; Erik Eberhardt; Oldrich Hungr; Derek Kinakin (2014) Empirical Runout Prediction for Open Pit Slope Failures in GEO2014. Ottawa, Ontario: Canadian Geotechnical Society.

@article{GeoRegina14Paper226,author = John Whittall; Erik Eberhardt; Oldrich Hungr; Derek Kinakin,title = Empirical Runout Prediction for Open Pit Slope Failures,year = 2014}