Impact of soft or stiff igneous intrusions and contact properties on the stability of room-and-pillar mines

In room-and-pillar mining, pillar stability depends on both the mechanical properties of the rock mass and the excavation geometry. While empirical methods typically assume homogeneous and isotropic conditions, many stratiform ore deposits are intersected by igneous intrusions, introducing heterogeneity. This study presents a comprehensive parametric analysis, implemented in COMSOL Multiphysics, to quantify the effect of dyke geometry, stiffness contrast, and contact strength on the stress distribution within rock pillars. Using the Arqueros Mine in Chile as a case study, we demonstrate that lithological contacts act as stress raisers and can locally increase the maximum compressive stress by up to 58% when the contact is relatively week, and by up to 29% when the contact is strong, relative to homogeneous conditions. Based on these results, we propose a set of correction factors to adjust safety factor estimations derived from traditional models. These correction factors provide a practical and replicable approach for evaluating the geomechanical performance of pillars affected by subvertical intrusions. Although stiffness parameters for host and intrusive rocks can be measured in the laboratory, contact stiffness remains difficult to quantify directly. We therefore recommend that future studies integrate numerical modelling with laboratory and field data to refine the representation of lithological contacts and improve design reliability in heterogeneous mining environments.