Seismic fragility analysis of reinforced concrete tunnels considering soil–structure interaction

This study aims to investigate the seismic fragility of reinforced concrete tunnels using pseudostatic analysis and equivalent linear site response analysis. Curvature ductility was adopted as the seismic damage index (DI), while the peak ground acceleration at the ground surface served as the intensity measure (IM). Both high- and low-frequency ground motions were considered to assess their effect on the structural fragility of tunnels. Fragility functions were derived using power law and exponential fitting, which is commonly employed for underground structures. The exponential fitting provided a stronger correlation between the IM and DI than the power-law fitting. Additionally, actual site profiles in South Korea, categorized by depth of bedrock and the stiffness of subsurface, were analysed. Results indicate that the tunnels in site profiles with deep bedrock and soft subsurface are more vulnerable to earthquakes than those in shallow bedrock with stiff subsurface. Furthermore, low-frequency ground motions caused a higher probability of tunnel damage compared to high-frequency ground motions.