Seismic Fragility of the SMART Tunnel Under Near-Field Earthquakes

This study investigates the seismic performance of the SMART Tunnel under near-field earthquake conditions, with a focus on how tunnel burial depth influences fragility, crack development, and structural response. The research began with a comprehensive literature review to establish a theoretical basis for seismic analysis and soil-structure interaction. Four 2D finite element models representing tunnel depths of 0 m, 5 m, 10 m, and 12.2 m were developed using ABAQUS, with realistic soil and structural properties. Seismic input was obtained from the PEER Ground Motion Database and processed through SeismoSignal to generate acceleration-time histories and response spectra. Time-history analyses were then conducted to simulate tunnel behaviour under selected near-field earthquakes. Key structural responses, such as stress distribution and crack propagation, were analysed to evaluate damages. Fragility curves were developed for each model to assess the probability of damage under varying seismic intensities. The findings show that Model 4, located 12.2 m above the rock layer, performs the best due to its ability to accommodate larger displacements before failure, benefiting from increased flexibility in softer soils. In contrast, Model 1, placed directly on the bedrock, was the least effective, showing early collapse under lower seismic loads. These results emphasise the importance of depth and soil interaction in seismic tunnel design.