ARTICLE Stability of mine development intersections — a probabilistic analysis approach Wael Abdellah, Hani S. Mitri, Denis Thibodeau, and Lindsay Moreau-Verlaan Abstract: Mine developments, such as haulage drifts, cross-cuts, and intersections, are the only way to access valuable ore from mining zones; they link mine developments with the nearest ore access points. Thus, they must remain stable throughout their service life or production plan. Mine development instability can cause production delay, loss of reserves, as well as damage to equipment and injury to miners. This paper presents a stepwise methodology to assess the stability of mine development intersections with respect to the mine production plan. A case study, the #1 Shear East orebody at Vale Garson Mine in Sudbury, Ontario, is presented. A three-dimensional, elastoplastic, finite difference model (FLAC 3D) is created to simulate the development of an inter- section situated 1.5 km below ground surface. The unsatisfactory performance of the intersection is evaluated in terms of strength- to-stress ratio with respect to mining sequence. A failure criterion is defined by a minimum strength-to-stress ratio of 1.4, and is used for mine developments (temporary openings). The intersection stability is evaluated at various mining stages and the modified “point-estimate method” (PEM) of (2n 2 + 1) is then invoked to study the probability of drift instability at the intersection. The results are presented and categorized with respect to probability, instability, and mining stage. Key words: mine developments, numerical modelling, point-estimate method (PEM). Résumé : Les puits d’extractions, les intersections et les galeries sont des lieux de passage nécessaires pour extraire les minéraux de la zone d’exploitation dans une mine. Ils relient les fronts d’exploitation aux lieux de décharge et de stockage et doivent par conséquent rester stables tout au long de la durée d’exploitation prévue lors de l’étape de planification. Des instabilités des de ces développements miniers peuvent conduire a ` des délais d’exploitation supplémentaires, des pertes de ressources, une distribution de contraintes induites accrue, ainsi que des dommages aux équipements et au personnel d’exploitation. Cet article présente méthode d’affirmation pas a ` pas une de la stabilité d’une intersection de galeries tout en respectant le plan de production. Une étude de cas du gisement Shear Est #1 dans la mine de Garson exploitée par Vale a ` Sudbury, Ontario est présentée. Une modélisation numérique trois-dimensionelle en comportement élastique–plastique avec le logiciel FLAC 3D est réalisée pour simuler le comportement d’une intersection de galeries a ` une profondeur de 1500 m. La probabilité de performance insatisfaisante est calculée aux différentes étapes de la séquence minière grâce au ratio contrainte/résistance. Le facteur de sécurité est fixé a ` 1,4 (ouvertures temporaires). La méthode de « point estimate » (2n 2 + 1) est utilisée pour calculer la probabilité de performance insatisfaisante. Les résultats sont présentés et classés selon les probabilités, le type d’instabilité et l’étape de la séquence minière. Mots-clés : développements miniers, modélisation numérique, point-estimation de la méthode (PEM). Introduction The sublevel stoping mining method with delayed backfill has been widely adopted by many Canadian metal mines. In this method, ore is mined out in stopes (blocks) that are drilled and blasted. The blasted ore from each stope is mucked out with load- ers and transported from a draw point to a nearby ore pass or dumping point. Mine development such as haulage drifts, cross cuts, and intersections are the only access where loaders and (or) trucks travel through, and thus must remain stable throughout their service life (Zhang 2006; Zhang and Mitri 2008; Wei et al. 2009, 2012; Abdellah et al. 2011, 2012, 2013). Mine development instability can result in production delays, loss of ore reserves, equipment damage, and even injuries. High and low stress levels that develop around mine developments due to mining activity can lead to a number of mining-induced failure mechanisms such as strainburst, caving, and closure, etc. Thus, it is important to properly use an efficient and timely ground sup- port system to mitigate these instability issues to provide safe access to production areas. Also, it is imperative to implement the ground support systems in combination with conventional geo- mechanical instrumentations (e.g., microseismic monitoring sys- tems, multiple position borehole extensometers (MPBX) and load cells) (Bawden et al. 2002; Charette 2012; Wei et al. 2012). Stability methods Stability assessment is one of the most important issues in min- ing ground control. Already recognized by rock mechanics prac- titioners; analytical methods such as those provided by Kirsch (1898), Ladanyi (1974), Brady (1977), and Brady and Lorig (1988) cannot provide adequate solutions for complex mining problems. Therefore, empirical methods, such as the stability graph method, have become widely used in Canadian underground mines. These methods are based on past experiences and rockmass classifica- tion systems. They employ certain geomechanical characteristics of the rockmass to provide guidelines on stability performance and to determine the rock support requirements. Received 29 March 2013. Accepted 7 November 2013. W. Abdellah and H.S. Mitri. McGill University, Montréal, QC H3A 0E8, Canada. D. Thibodeau and L. Moreau-Verlaan. Vale Ltd., Sudbury, ON P0M 1N0, Canada. Corresponding author: Wael Abdellah (e-mail: wael.abdellah@mail.mcgill.ca). 184 Can. Geotech. J. 51: 184–195 (2014) dx.doi.org/10.1139/cgj-2013-0123 Published at www.nrcresearchpress.com/cgj on 18 November 2013.