Evaluating 2D and 3D slope stability in a complex open-pit mine: a CAD-based numerical study

Accurate slope stability assessment is essential for the safe and economical operation of deep open-pit mines, especially in areas with complex geological and hydrological conditions. While two-dimensional (2D) analyses are still widely used in engineering practice, they struggle to accurately reflect true failure mechanisms in three-dimensional (3D) environments. This study offers a comprehensive comparison between 2D and 3D slope stability analyses specifically for the Sungun open-pit copper mine in Iran. A detailed 3D base model was developed using Rhinoceros and Griddle to accurately represent the pit geometry, geotechnical domains, and groundwater surface. This model facilitated the generation of a hexahedral mesh for FLAC 3D simulations and allowed for the extraction of multiple 2D cross-sections for FLAC analyses in various directions. The 3D model predicted a rotational failure mechanism, yielding a global safety factor ( FS 3D ) of 1.285, which was validated against field observations of tension cracks and active slope deformation. In contrast, the comparative 2D analyses produced varying results based on the orientation and location of the sections, with FS 2D values ranging from 1.04 to 4.11. While some 2D sections approximated FS 3D values reasonably, none accurately captured both the geometry and extent of the failure surface. Notably, sections aligned with the primary direction of displacement (North-South) yielded the most representative results. These findings underscore the limitations of relying solely on 2D analyses for pit slope design in geologically complex settings. The integration of 3D numerical modeling with CAD-based geometry management is crucial for achieving reliable slope stability assessments and for minimizing design uncertainties in large-scale mining projects.