Seismic risk evaluation of highway tunnel groups.

Abstract

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 usercosts. Earthquakes are the hazard that most afect the tunnels’ serviceability. Dependingon the structural damage’s magnitude, the serviceability loss can be at diferent degrees,from marginal changes in trafc fow, associated with minor damages, to trafc interruption, associated with collapsing. Because of seismic phenomena’ randomness nature,its efect on tunnel serviceability is estimated in probabilistic terms. Trafc interruptionprobability was estimated using fragility curves, representing the probability of achievinga specifc damage state regarding the seismic hazard intensity. The calibration of tunnelfragility curves requires large samples of damages, seismic intensities, and geological andconstructive data, which are not always available, especially in countries with a small number of tunnels in their road network. This work proposes a simplifed procedure for evaluating the tunnels’ trafc interruption probability due to earthquakes. The approach proposeduses existent seismic exposures maps, a strategy for selecting from existing fragility curvesthe more suitable, and a simple method to estimate the trafc interruption probability. Theprocedure analysed 20 tunnels afected by the Maule earthquake in Chile. These tunnelsexperimented PGA between 0.12 and 0.36 g. The highest risk values were obtained in tunnels without alternative routes and high repairing costs.