Seismic vulnerability of circular tunnels in sand

The paper is focused on the assessment of seismic fragility curves for circular tunnels under moderate to severe earthquakes with aim improving reliability risk underground infrastructural networks. Non-linear two-dimensional dynamic analyses were performed different tunnel and soil configurations by using finite-difference method implemented in Flac2D software. applied input motions selected considering their amplitude frequency content variability. response accelerations predominant frequencies computed at ground level, above tunnel, compared corresponding free-field results distinguish effects attributable presence from those due site amplification. Tunnel safety was assessed through curves, taking into account dependence lining bending resistance axial force variation during earthquake. more effective intensity measure investigated correlating performance peak velocities level bedrock depth, respectively. resulting showed a satisfying matching empirical ones, generated basis observed damage tunnels.