The instability of underground excavations developed in serpentinite rock masses at the Bou-Azzer cobalt mine in Morocco has long been a critical concern for geotechnical engineering. The challenges encountered in two previous strategic projects, at depths of ۳۶۰ meters and ۵۱۰ meters, were mainly attributed to stress conditions exceeding the rock strength, leading to significant reductions in the cross-sectional area of the excavations and severe deformation of the installed support systems. Conventional empirical support design approaches applied at the mine have shown clear limitations when dealing with serpentinite rock masses. Another limitation of these methods is that they do not allow for the assessment of support system performance and deformation control to improve the stability of such deep excavations. The primary objective of this study is to develop a reliable support system capable of ensuring a safe working environment for personnel and equipment through numerical modeling of excavation behavior at a depth of ۵۴۰ meters, corresponding to the new mine extension. The adopted methodology is based on detailed two-dimensional finite element modeling, explicitly accounting for the variability in the mechanical behavior of the serpentinite rock mass and its interaction with the proposed support systems through a site-specific analysis. Numerical simulations were conducted for different serpentinite types under two analysis scenarios: excavations during development and excavations with installed support. The results indicate that maximum displacements are critically high in type ۴ serpentinite and remain substantial in type ۱ serpentinite. By contrast, moderate displacement values were observed in type ۲ and type ۳ serpentinites. However, once the proposed support measures were implemented, the maximum displacements were reduced to acceptable limits with respect to the excavation span and height, and the safety factors improved to between ۱.۱۰ and ۱.۳۰ for the crown and from ۱.۱۰ to ۱.۶۰ for the sidewall. Numerical modeling has proven to be an effective decision-support tool for deep underground excavations in complex rock conditions. The findings of this study provide a practical and reliable basis for designing support systems in deep mining environments, with approaches that can be extended to other sites facing similar geotechnical challenges.
