Stability of mine development intersections--a probabilistic analysis approach

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 ore-body 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 intersection 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.sup.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). Les puits d'extractions, les intersections et les galeries sont des lieux de passage necessaires pour extraire les mineraux de la zone d'exploitation dans une mine. Ils relient les fronts d'exploitation aux lieux de decharge et de stockage et doivent par consequent rester stables tout au long de la duree d'exploitation prevue lors de l'etape de planification. Des instabilites des de ces developpements miniers peuvent conduire a des delais d'exploitation supplementaires, des pertes de ressources, une distribution de contraintes induites accrue, ainsi que des dommages aux equipements et au personnel d'exploitation. Cet article presente methode d'affirmation pas a pas une de la stabilite d'une intersection de galeries tout en respectant le plan de production. Une etude de cas du gisement Shear Est #1 dans la mine de Garson exploitee par Vale a Sudbury, Ontario est presentee. Une modelisation numerique trois-dimensionelle en comportement elastique-plastique avec le logiciel FLAC 3D est realisee pour simuler le comportement d'une intersection de galeries a une profondeur de 1500 m. La probabilite de performance insatisfaisante est calculee aux differentes etapes de la sequence miniere grace au ratio contrainte/resistance. Le facteur de securite est fixe a 1,4 (ouvertures temporaires). La methode de << point estimate >>([2n.sup.2] +1) est utilisee pour calculer la probabilite de performance insatisfaisante. Les resultats sont presentes et classes selon les probabilites, le type d'instabilite et l'etape de la sequence miniere. Mots-cles: developpements miniers, modelisation numerique, point-estimation de la methode (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 [...]