Seismic risk evaluation of highway tunnel groups

Tunnels allow the continuity of rural road and urban transportation networks. Their shutdown provokes a loss in the transport system’s level service, which entails higher road user costs. Earthquakes are the hazard that most affect the tunnels’ serviceability. Depending on the structural damage’s magnitude, the serviceability loss can be at different degrees, from marginal changes in traffic flow, associated with minor damages, to traffic interruption, associated with collapsing. Because of seismic phenomena’ randomness nature, its effect on tunnel serviceability is estimated in probabilistic terms. Traffic interruption probability was estimated using fragility curves, representing the probability of achieving a specific damage state regarding the seismic hazard intensity. The calibration of tunnel fragility curves requires large samples of damages, seismic intensities, and geological and constructive data, which are not always available, especially in countries with a small number of tunnels in their road network. This work proposes a simplified procedure for evaluating the tunnels’ traffic interruption probability due to earthquakes. The approach proposed uses existent seismic exposures maps, a strategy for selecting from existing fragility curves the more suitable, and a simple method to estimate the traffic interruption probability. The procedure analysed 20 tunnels affected by the Maule earthquake in Chile. These tunnels experimented PGA between 0.12 and 0.36 g. The highest risk values were obtained in tunnels without alternative routes and high repairing costs.