Vulnerability analysis of subsea immersed tunnels considering seismic motion ensembles with different spectral characteristics

The immersed tunnel of the Hong Kong–Zhuhai–Macao Bridge was used to investigate how ground-motion spectral characteristics affect seismic vulnerability assessment. A two-dimensional model considering soil–structure interaction was established, and incremental dynamic analysis was conducted under far-field and near-field record sets. Fragility curves were developed using inter-story drift ratio as the damage measure and PGA as the intensity measure. Results show that record ensemble spectral characteristics significantly influence the estimated post-earthquake failure probability of immersed tunnels, with the effect increasing at higher seismic intensity. Compared with near-field records, far-field records predict lower failure probabilities, supporting performance-based seismic design of immersed tunnels.