Seismic performance of soil–tunnel–building systems in stiff soils

In order to study seismic soil–tunnel–building interaction in stiff soils, a metro station currently under construction, located near by a 5-story masonry building, was selected as a test site for seismic instrumentation. The site is in Mexico City, in the so-called hill zone, where very cemented sandy silt and silty sands can be found. An arrangement of five accelerometers were deployed, to assess free-field, near-field, and building seismic response. This article presents the results gathered from the seismic instrumentation after recording five low- to high-magnitude earthquakes (i.e. ranging from 4.8 to 7.7 Mw) from both interface and intraplate events. The results clearly indicate that even in low- to medium-magnitude events, the presence of the tunnel leads to peak ground acceleration (PGA) amplification both in the horizontal and vertical components, ground motion incoherence, and spectral accelerations (Sa) amplification at high frequencies. Although Sa amplification is more important for intraplate and interface low- to medium-magnitude events, frequency content modification occurs regardless of the earthquake magnitude. These facts must be accounted for when designing low- to medium-rise structures underlaid or nearby underground infrastructure such as tunnels in highly populated urban areas.