Stability Analysis and Design of Support System for Adits of the Gold Deposits of Mazraeh-Shadi Using Numerical Modeling

The present study proposes a suitable support system for the underground tunnels of the gold deposits of Mazraeh-Shadi in the East Azerbaijan Province of Iran using numerical modeling. The stability of the tunnels was evaluated using the data obtained from the numerical modeling, the ground reaction curve (GRC), the longitudinal deformation profile (LDP), permissible displacements according to the Sakurai relationships, and the load imposed on the support system of the tunnels. Due to the very large dimensions and high computational costs, the adits were modeled at the depths of 1830 and 1870 meters. According to the results and the diagram of the proposed support system based on Q and the cross-section of the tunnel, a support system made from fiber shotcrete with a thickness of 90-120 mm, along with rock bolts regularly installed, is proposed. At the intersections and the tunnel portal, a stronger support system had to be used, and in the tunnel portal the reinforcement system, such as the implementation of shotcrete on the sloped surface, should be taken.  At the level of 1870 meters, implementing shotcrete with a thickness of 12 cm and a safety factor of 1.2 was sufficient. At the level of 1830 meters, the shotcrete required to be strengthened. For this purpose, a layer of steel mesh or a restraining lattice with a spacing of 2 meters was used. The proposed support system is sufficient and appropriate given the relatively small dimension of the tunnels and their temporary use and according to the Sakurai criterion, the experimental methods, and the engineering judgment.