Experimental and Numerical Investigation of the Effect of Rock Mass Behavior and Stratum Orientations on Horseshoe‐Shaped Tunnel Stability

ABSTRACT This study investigates tunnel stability within sedimentary rock masses characterized by multiple joint sets and challenging geological conditions. The behavior of stratified rock masses around an excavation depends on both the intact rock and the combination of dominant and bedding joints. The main objective of this study is to highlight the convergence and deformation in rock masses around horseshoe‐shaped tunnels using an integrated methodology that combines field investigations, finite element modeling, and pull‐out test results. Statistical analysis confirmed the robustness of the 3D modeling approach for reproducing in situ behavior and creating realistic models of heterogeneous, anisotropic rock masses. The numerical results indicate that the highest displacement ratio is concentrated at the intersection of the bedding and dominant joints with dip angles ranging from 0° to 45°, which should be considered as critical dip angles for mining progress. Indeed, wedge and sliding failure zones developed on the roofs and left rib, respectively. Increasing depth reduced the influence of rock mass quality, particularly for GSI chart values ranging between 35 and 40, resulting in significant convergence around the excavation. The support system emphasizes the effectiveness of systematic bolting in competent rock masses. Moreover, the pull‐out tests revealed that the load‐bearing capacity of the split‐set bolts increased substantially when the bedding approached vertical orientations θ = 90°, and the compressive strength exceeded 39.6 MPa, conditions that promote safer tunneling through vertical stratum orientations. These findings enhance the understanding of tunneling stability mechanisms in stratified rock masses with multiple joint sets under various geological conditions.