Seismic risk of mined tunnels

The seismic response of structures is the main line of research currently being developed by Dr. Gabriel Candia, an academic from the School of Engineering at Universidad del Desarrollo. Recent earthquakes worldwide have caused major direct losses due to damaged infrastructure. The 2010 Maule earthquake alone generated losses over 30 billion USD, and costs skyrocketed for construction, labor, and insurance premiums; however, tunnels and buried pipelines built on stiff soils performed very well, and no major damages were reported. A similar response was observed in the LA Metro (Northridge earthquake 1994), Athens Metro (Athens earthquake 1999), and Taipei Metro (Chi-Chi earthquake 2002). On the other hand, and contrary to the general notion of the seismic safety of tunnels built on stiff soil, the latest experimental results have shown that these tunnels are indeed highly vulnerable systems during strong earthquakes. This apparent discrepancy about tunnel performance is the focus of Candia’s current research.

Despite the recent advances in ground motion characterization and the sophistication of current numerical tools for evaluating the tunnel response, quantifying the seismically induced damage and losses is still cumbersome. Moreover, current design practices provide no estimates of the tunnel performance variability or the rate of occurrence of damage parameters, which makes the seismic loss assessment yet more difficult. The goal of this research is to estimate damage and loss fragility functions for a circular mined tunnel in stiff soil deposits, and test the main working hypothesis “Mined tunnels in stiff soil designed for static loads can withstand severe ground motions without significant damage”. For this purpose, and to constrain the number of variables involved, the study will focus on circular dual track tunnel in stiff soils, excluding any form of ground failure.

 Finite element mesh of circular mined tunnels in stiff sand modeled in OpenSees