Seismic damage evaluation of an entire underground subway system in dense urban areas by 3D FE simulation

Underground structures often pass beneath high-rise buildings or are located close to them in megacities. Given complex site-city interactions, conventional earthquake engineering practices may leave megacities in seismically prone areas in potential danger. Rather than focusing purely on the interaction between soil and either surface structures or underground structures, this study aims to explore the earthquake-induced hazard of a dense urban area with an entire subway station, two long subway tunnels and 36 fully modeled high-rise piled frame buildings. The study is conducted through the 3D fully coupled dynamic analysis in both the time and frequency domains, emphasizing the influence of aboveground buildings on underground structures. The results reveal that the existence of aboveground buildings generally decreases the station's response and can either increase or decrease the subway tunnel's responses. The presence of either aboveground structures or underground structures affects the wavefield and in turn the responses of adjacent structures, highlighting the importance of considering soil-city interactions. The station is most dangerous at the columns' bottoms. The existence of subway stations and tunnels increases the nearby peak ground accelerations.