Three‐Dimensional Seismic Response Analysis of Tunnels in Layered Media Using Modified Domain Reduction Method

Fault inclination and complex geological soil features significantly impact the seismic response of underground unlined tunnels. Modeling fault rupture mechanisms necessitates spanning the computational domain over several kilometers, thus making the approach computationally inefficient. In this study, an efficient modeling algorithm, named as multi‐layer Modified Domain Reduction Method (MDRM), has been proposed to analyze the Soil‐Fault‐Tunnel (SFT) system in layered soil media. The study has demonstrated the effectiveness of the MDRM for modeling the SFT system in layered soil media, considering the seismic source, wave propagation path, and local site effects for realistic seismic response assessment of the tunnels. The MDRM algorithm is implemented in an open‐source finite element package, MASTODON (Multi‐hazard Analysis for STOchastic time‐DOmaiN phenomena), based on the MOOSE numerical framework. Using the MDRM approach, parametric simulations for four different fault rupture mechanisms and three distinct tunnel cross‐sections (all having the same opening area) are being performed to capture the overall seismic response of the tunnels. The results provide insights into the influence of fault inclination angle, surface wave generation, and local site effects on the response. The transfer function profiles for the considered soil layers are contrasted, and their influence on different tunnel cross‐sections is investigated. The findings are useful in the efficient and reliable design of underground tunnels in multi‐layered media subjected to different fault rupture mechanisms.