Journal of Korean Tunnelling and Underground Space Association ISSN:2233-8292(Print) 2287-4747(Online) 한국터널지하공간학회 논문집

This research investigates the mechanical impact of shaft inclination, an unavoidable construction tolerance, on the structural stability of deep shafts in multi-layered geological formations. Circular shafts are generally designed to secure stability through the stress arching effect based on geometric symmetry. However, in practice, inclinations often exceed design tolerances due to the mechanical limitations of drilling equipment, asymmetric distribution of discontinuities, and geological heterogeneity. In this study, numerical analyses were performed using the Three-Dimensional Distinct Element Method (3DEC) to evaluate the impact of shaft inclinations (0°, 5°, 10°, 15°) on composite strata consisting of weathered, soft, and hard rock. The results demonstrate that increasing inclination disrupts symmetric stress states, significantly accelerating shear stress concentration at geological interfaces where material stiffness changes abruptly. Notably, the displacement amplification rate in weak weathered rock layers reached up to 210% compared to the perfectly vertical state. Furthermore, asymmetric loading on rock bolts and shotcrete indicated a potential risk of support capacity failure in specific sectors. These findings provide a theoretical foundation for differential reinforcement strategies based on geological profiles and construction tolerances in deep shaft projects.