Site specific seismic performance of circular tunnels in dry sand

Past earthquakes revealed that underground tunnel structures are exposed to seismic risk and their seismic vulnerability is mainly function of the tunnel structure technology, the soil-tunnel interaction developing during the seismic shaking and the intensity of the seismic event. Each of these factors play an important role in terms of the probability of damage and loss of functionality due to the tunnel deformations in- duced by increments in internal forces. Currently, the fragility curves are among the most widespread methods for the rapid assessment of structural performance at different hazard levels, giving the probability of reaching a defined damage level with respect to a given level of seismic motion. In the present work, a recently developed approach to evaluate the seismic risk has been applied to circular tunnels, whereby the main focus is the expression of the failure annual rate through the convolution of the fragility of the system under investigation and the seismic hazard on site. In this way, a direct link be- tween the performance of the structure with its measuring parameter is established. The procedure has been adopted for some reference tunnel sections of the Metro Line of Naples.