The seismic response and resilience of nearby underground infrastructures

To assess the seismic resilience of civil structures and infrastructures, a detailed investigation of their response to strong motions is required. However, while the effects of major and minor earthquakes on above-ground infrastructures (e.g. road bridges) are relatively well-known, fewer studies have addressed underground ones (e.g. shallow or deep tunnels). In fact, while many bridges are heavily instrumented, few tunnels are equipped with the sensor networks needed for proper structural health monitoring. On the one hand, it is well-expected that both underwater and mountain tunnels will suffer much less significant structural damage than bridges. Nevertheless, research works on their respective responses, analysing comparatively different kinds of tunnels under the same seismic input, are lacking. This is even more true for studies involving recorded data and quantitative measurements. Here, the dynamic responses of one shallow underwater tunnel, built using the immersed tube technique in soft soil, and one deep tunnel, excavated in sandstone and shale rock, are directly compared. These two infrastructures are located close to each other in the San Francisco Bay Area and endured a very close near-fault earthquake. The results show that the tunnel in hard rock guaranteed a higher seismic resilience than the underwater tunnel dug in soft soil.