The Geological Influences of Glacially Rafted Clearwater Formation on the Design and Operation of an External Tailings Facility

Andrew I. Bayliss, Lucy Philip, Karen Masterson, Raymond Wong, Mohd Rahman, Daniel Hepp, Michael Clarke, Scott Martens, Mahmoud Elbanna

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

Session: Engineering Geology and Rock Mechanics

ABSTRACT: Glacial rafts are glaciotectonic structures that can exhibit similar geotechnical properties and fabric to that of the parent geological unit. They can present a significant geohazard for the design and operation of dams and infrastructure. The Jackpine Mine External Tailings Facility, which is operated by Shell Canada Energy, is underlain by glacial rafts derived from the Clearwater Formation. The Clearwater Formation is a weak, overconsolidated clay-shale known to influence the stability of several existing tailings dams in the Fort McMurray region due to mobilized residual strength and a high pore pressure response to loading. A previous case study by the authors focused on the distribution and geotechnical parameters of glacial rafts beneath the eastern component of the external tailings facility, known as Sand Cell 2. This paper builds on the findings of that earlier study and summarizes the use of drilling programs, laboratory testing, geological modelling, instrumentation data, and the Observational Method to manage geotechnical uncertainty in the design of the entire external tailings facility. RÉSUMÉ Les blocs erratiques sont des structures glaciotechtoniques qui peuvent présenter des propriétés géotechniques similaires à celles de l'unité géologique mère. Ils peuvent poser un géorisque significatif lors du design et de l'opération de digues et d'infrastructures. Le complexe de résidus miniers externes de la mine Jackpine, opéré par Shell Canada Energy, comporte des blocs erratiques enfouis provenant de la formation de Clearwater. La formation de Clearwater est composé d'un shale argileux surconsolidé et faible, reconnu comme influençant la stabilité de plusieurs digues à stériles dans la région de Fort McMurray en raison de sa force résiduelle mobilisable et d'une pression interstitielle réactive à l'application d'une charge. Une étude de cas précédente, des mêmes auteurs, se concentrait sur la distribution et sur les paramètres géotechniques des blocs erratiques sous la partie Est du complexe de résidus miniers externe, connu sous le nom de Sand Cell 2. Le présent article se fonde sur les conclusions de cette précédente étude, et décrit brièvement l'utilisation de campagnes de forage, de tests en laboratoire, de modélisation géologique, de données d'instrumentation et de méthodes observationnelles afin de gérer les paramètres géotechniques incertains dans le design de l'ensemble du complexe de résidus miniers externe. 1 INTRODUCTION A previous study by the Authors (Bayliss et al, 2013) focused on the distribution and geotechnical properties of the glacially rafted bedrock (PgKc1) beneath the easternmost component of an External Tailings Facility (ETF) at Jackpine Mine (JPM), Fort McMurray, Alberta, Canada, known as Sand Cell 2 (SC2). The PgKc was thought to be derived from the Clearwater Formation (Kc), which is a weak, overconsolidated, clay-shale known to influence the stability of several existing ETF's in the Fort McMurray region due to mobilized residual strength and a high pore pressure response to loading. PgKc is also present beneath the operational components of the ETF, known as the Dedicated Disposal Facility 1 (DDA1) and Sand Cell 1 (SC1). The design of the ETF has been a continual process since 2007 and our understanding of the PgKc has evolved through performance and drilling data. This paper builds on the 1 Geological codes are based on SCE's reference system findings of the SC2 study and summarizes how drilling data, laboratory testing, geological modelling, performance data and the Observational Method (OM) has been used in the design process to manage geotechnical uncertainty of the PgKc. 2 GLACIAL RAFTS Glacial rafts are stratigraphically out of sequence, glaciotectonic structures that exhibit similar geotechnical properties and fabric to that of the parent geological unit. Ruszczynska-Szenajch (1997) described rafts as 'fragment of unconsolidated or poorly cemented substratum with preserved lithological character, detached from its primary bed and transported due to glacial activity, and which occurs within or immediately adjacent to corresponding deposits'. Glacial rafts are typically associated with micro-glaciotectonic structures such as slickensides, boudins, folds, faults and brecciation. On the macro-scale, glacial rafts can form part of landforms such as thrust moraines or hill / hole pairs.

RÉSUMÉ: eological Influences of Glacially Rafted

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Andrew I. Bayliss; Lucy Philip; Karen Masterson; Raymond Wong; Mohd Rahman; Daniel Hepp; Michael Clarke; Scott Martens; Mahmoud Elbanna (2014) The Geological Influences of Glacially Rafted Clearwater Formation on the Design and Operation of an External Tailings Facility in GEO2014. Ottawa, Ontario: Canadian Geotechnical Society.

@article{GeoRegina14Paper262,author = Andrew I. Bayliss; Lucy Philip; Karen Masterson; Raymond Wong; Mohd Rahman; Daniel Hepp; Michael Clarke; Scott Martens; Mahmoud Elbanna,title = The Geological Influences of Glacially Rafted Clearwater Formation on the Design and Operation of an External Tailings Facility ,year = 2014}