A Case Study on Tunnel Excavation Stability of Columnar Jointed Rock Masses with Different Dip Angles in the Baihetan Diversion Tunnel

Columnar jointed rock mass (CJRM) formed by intact divided special symmetrical columnar joints is a type of with poor mechanical properties, strong anisotropy, and weak self-supporting ability, severely affecting the excavation safety stability underground tunnels. In this study, taking Baihetan hydropower station as engineering background, CJRM geological numerical models different dip angles that combined well natural were generated based on statistical parameters site verified to have high rationality accuracy. Tunnel overloading tests carried out these models, results showed stress displacement distributions after exhibited anisotropic characteristics under angles, positions where problems are most likely occur side walls, which prone stress-structure-controlled failure mode. The ability at from 45°, 60°, 75°, 90°, 30°, 0°, 15°. factors assessed for 0–90° degrees 2.5, 2.6, 1.8, 2.1, 2.2, respectively, providing valuable reference construction support measures excavation.