Theoretical and Numerical Simulation Study on Train Running Safety of Existing Scoured Bridges in High-Speed Railways Under Seismic Action

Scour has become one of the primary causes of bridge failures. However, the vibration response of train-bridge coupled systems under seismic action in scoured bridges remains unknown, which is critical for train operational safety. This study employed train-bridge coupled vibration theory and the m-method considering pile-soil interaction to establish a coupled train – track – bridge – pile group vibration model for under scour conditions. The influence of scour depth on system dynamics was quantified, and seismic effects were analyzed through ground motion excitation. The results show that bridge foundation scour predominantly amplifies lateral structural responses, affecting displacement more significantly than acceleration and exceeding speed-induced effects. At 300 km/h, rail lateral displacement, derailment coefficient, wheel load reduction rate, and wheelset lateral force approach critical thresholds, recommending a 300 km/h operational limit. Train safety indices increase markedly with speed but exhibit no monotonic trend with scour depth; speed dominates scour in dynamic response influence. Seismic activity proportionally amplifies lateral displacements with scour depth. Seismic effects surpass scour in governing system dynamics. Neglecting earthquakes underestimates safety indices, risking operational misjudgment. Consequently, neglecting the impact of seismic activity may underestimate the train running safety index on the bridge, potentially leading to misjudgment of train running safety.