Water inflows through fracture networks are a major economic and safety issue in underground mines. Although pre-grouting of pilot holes during mine development efficiently reduces water inflows into mine excavations, current design methods remain empirical. We used a finite-element numerical model to simulate groundwater inflow into a stope with the objective of finding the best configuration to increase pre-grouting efficiency for sealing faults while decreasing the associated costs. We designed simulations to test various grout injection scenarios for two different major fault locations around the stope, based on the site characteristics of the Éléonore mine (Québec, Canada). Sensitivity analyses show that, for a fault located above the stope, grouting the zone between the fault and the stope reduces inflow more than directly grouting the fault. Also, in the case of a fault intersecting a stope, the simulations suggest that the fault itself should be grouted as widely as possible, instead of sealing only the immediate surroundings of the stope. © 2019, Springer-Verlag GmbH Germany, part of Springer Nature.