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Stress-induced failure is among the most common causes of instability in Canadian deep underground mines. Open stoping is the most widely practiced underground excavation method in these mines, and creates large stopes which are subjected to stress-induced failure. The probability of failure (POF) depends on many factors, of which the geometry of an open stope is especially important. In this study, a methodology is proposed to assess the effect of stope geometrical parameters on the POF, using numerical modelling. Different ranges for each input parameter are defined according to previous surveys on open stope geometry in a number of Canadian underground mines. A Monte-Carlo simulation technique is combined with the finite difference code FLAC3D, to generate model realizations containing stopes with different geometrical features. The probability of failure (POF) for different categories of stope geometry, is calculated by considering two modes of failure; relaxation-related gravity driven (tensile) failure and rock mass brittle failure. The individual and interactive effects of stope geometrical parameters on the POF, are analyzed using a general multi-level factorial design. Finally, mathematical optimization techniques are employed to estimate the most stable stope conditions, by determining the optimal ranges for each stope’s geometrical parameter. Keywords: Stope stability, Stope geometrical parameters, Probability of failure, General factorial design, Numerical modeling, Sublevel open stoping

Study region: The study of groundwater chemistry of the Charlevoix/Haute-Côte-Nord (CHCN) region in the province of Quebec in Canada is part of a regional hydrogeological characterization project. Study focus: Groundwater was sampled in 113 wells over the 4500 km2 study area and analyzed for 39 parameters including major, minor, trace and inorganic constituents, plus stable isotopes 2H and 18O. Two multivariate statistical methods, hierarchical cluster analysis (HCA) and R-mode factor analysis (RFA) were combined with graphic methods to classify the samples according to plausible levels of groundwater evolution in that region. New hydrological insights for the region: Four sample clusters were identified. Cluster 1 is composed of low-salinity Ca-HCO3 groundwater corresponding to recently infiltrated water in surface granular aquifers in recharge areas. Cluster 4 Na-(HCO3-Cl) groundwater is more saline and corresponds to more evolved groundwater probably from confined bedrock aquifers. Cluster 2 and Cluster 3 (Ca-Na)-HCO3 and Ca-HCO3 groundwater, respectively, correspond to mixed or intermediate water between Cluster 1 and Cluster 4 from possibly interconnected granular and bedrock aquifers. This study identifies groundwater recharge, water–rock interactions, ion exchange, solute diffusion from marine clay aquitards, saltwater intrusion and also hydraulic connections between the Canadian Shield and the granular deposits, as the main processes affecting the hydrogeochemical evolution of groundwater in the CHCN region.