Development of Seismic Fragility Curve for Railway Tunnel Crossing Fracture Zone

This study investigates the seismic fragility of railway tunnels intersecting fractured geological zones using a nonlinear numerical approach. A series of dynamic analyses was performed on tunnel models subjected to multiple ground motions with varying frequency contents. The structural response was evaluated in terms of maximum bending moment, and the resulting damage indices were used to classify damage states. Based on these classifications, seismic fragility functions were developed for tunnels passing through fractured zones using a lognormal cumulative distribution with peak ground acceleration (PGA) as the intensity measure. The fragility curves indicated that the probabilities of exceeding minor, moderate, and extensive damage states surpassed 50% at PGAs of approximately 0.289 g, 0.578 g, and 0.91 g, respectively. These findings highlight the elevated seismic risk in tunnels intersecting fractured ground and emphasize the necessity of incorporating geological conditions into seismic design frameworks.