In seismically active regions with active fault systems, the safe design and construction of tunnels consistently pose significant technical and geotechnical challenges. Segmental tunnels, as one of the most common tunneling methods in underground projects, are highly susceptible to fault-induced ground movements. Understanding how various tectonic fault types—including reverse, normal, and strike-slip faults—affect the structural stability of tunnels, particularly under varying geotechnical and geometrical conditions, plays a key role in enhancing their safety and durability.In this study, the behavior of segmental tunnels subjected to active faults is investigated through numerical modeling using FLAC3D software. A parametric sensitivity analysis was conducted on segment thickness, soil mechanical properties, tunnel depth, and fault dip angle, evaluated through four types of numerical errors: discretization, convergence, rounding, and modeling errors. The results showed that a mesh size of 10 cm reduces the discretization error to 4.09%, and applying an unbalanced force criterion less than 1×10⁻⁵ ensures model convergence. In reverse faults, increasing the segment thickness and employing soft soil conditions reduce displacement. In normal faults, tunnel depth and fault angle have the greatest influence on ring separation. For strike-slip faults, loose soils combined with vertical fault angles contribute to minimizing deformations. These findings provide valuable guidance for optimizing tunnel design in active seismic zones.