Optimization of Tunnel Support Systems in High-Stress Geological Zones: A Case Study of Diamer-Basha Dam

Excavating large-scale tunnels in tectonically active regions, such as the Himalayan seismic zone, challenges the stability of underground structures due to high in-situ and induced stresses. The Diamer-Basha Dam (DBD) project involves complex tunneling through heterogeneous bands of granite and diorites, necessitating an engineered support system to mitigate progressive rock mass failure. In Pakistan, the tunnel support often relies on empirical classifications like the Rock Mass Rating (RMR) and Q-system. These systems provide a useful initial estimate; however, their direct application without site-specific calibration frequently results in conservative or over-designed support systems. This study investigates an optimized support framework by integrating empirical characterization with numerical Finite Element Method (FEM) analysis. Using geological data acquired from the site, including face maps and borehole logs, we classified rock mass and simulated its response to excavation using RS2 software. The research specifically evaluates the mechanical efficacy of Fiber Reinforced Shotcrete against optimized combinations of plain shotcrete and active rock bolts. Numerical simulations indicate that the in-situ rock mass possesses sufficient self-supporting capacity in specific zones to allow for a reduction in shotcrete thickness when supplemented with bolting. The models demonstrate that optimized designs maintain the required structural stability while reducing material consumption. These findings suggest that a hybrid empirical-numerical framework offers a cost-effective engineering solution for large excavations. By validating support performance through numerical modelling, this study provides a repeatable framework for optimizing tunnel support in complex geological environments.