Abstract: Previous research shows that the stability of open pit mines transitioning to underground mining is a critical issue for practitioners and researchers. However, previous studies have not adequately addressed the effects of geomechanical properties of host rocks on the mine stability. To address this gap, in this thesis has presented a comprehensive investigation of geomechanical parameters, including the angle of internal friction, elastic modulus, cohesion, and Poisson's ratio. The study employs the Finite Difference Method and FLAC3D software with the Mohr-Coulomb structural criterion for the analysis. For this study, the Goshfil mine in Isfahan was chosen as a case study due to its history of both open pit and underground mining. Based on the mine topography data the Goshfil mine geometry was extracted, which was then used to create the numerical model geometry in FLAC3D software. Then, the model excavation was carried out gradually, taking into consideration the elastic behavioral model, and the initial balance of the model was established following pit creation. Considering the mining execution method, gradual pit excavation was deemed necessary to avoid any shocks to the model and prevent any false uplifts in the model's bottom. Once the in-situ stresses in the pit were formed, the behavioral model was changed into the Mohr-Coulomb plastic model, and the model was solved until it reached an equilibrium state. The main objective of this investigation was to analyze the surface displacements and settlements caused by underground mining. After the model achieved equilibrium, all displacements were reset to zero to enable the accurate eva‎luation of post-underground mining displacements. Considering the uncertainty in the eva‎luated geomechanical parameters of the host rock, a sensitivity analysis was conducted on the variations in the geomechanical properties of the mine slopes, specifically the limestone slope. To achieve this, numerical simulations were carried out, where 36 different scenarios of cohesion, elastic modulus, angle of internal friction, and Poisson's ratio were examined. This study examines the influence of geomechanical parameters on the settlement around the pit, maximum settlement within the pit, roof displacement, and uplift of underground stopes. The impact of these parameters varies in different sections of mine, but the angle of internal friction has the most significant effect on displacements resulting from underground mining. Specifically, a higher angle of internal friction reduces the vertical displacement, while a lower angle of internal friction increases both settlement and displacement. At an angle of internal friction of 40 degrees vertical displacement is the lowest, while the impact is particularly pronounced at an angle of internal friction of 20 degrees, where the allowable limit for settlement expands considerably. The results also indicate that increasing cohesion can lead to a maximum settlement reduction of up to 50%, with a relatively smaller impact on the underground stope. In contrast, elastic modulus has a more substantial effect on the underground stopes than on the maximum settlement. Specifically, when an elastic modulus of 1 GPa is applied, the impact is more pronounced than when using elastic modulus of 2 or 4 GPa. Further, Poisson's ratio was examined as another parameter, which was found to have a minor effect on the vertical displacements.

سعيد مهدوي

امين ازهري , ابراهيم قاسمي