Seismic Fragility Analysis for Probabilistic Risk Assessment of Underground Structures

The seismic assessment of urban tunnels, crucial for city infrastructure, particularly shallow tunnels in transportation systems, is vital for risk mitigation. This study focused on the Ahwaz twin tunnels in Iran, using incremental dynamic analysis and probabilistic risk assessment. Evaluating seismic behavior through 15 earthquake records, the study generated fragility curves for operational, minor, moderate, and extensive damage states. Results indicate a 99.5% probability of operational limit at a PGA of 0.35 g, with seismic risk assessment aligning with safety class 3 of the Swedish Transportation Administration.