Seismic fragility analysis of shield tunnels in liquefiable layered deposits

Abstract

Ensuring the structural resilience of shield tunnels is critical in seismically active regions. Liquefaction induced by seismic activity poses an additional hazard to tunnel safety. The study performed seismic fragility analysis using the incremental dynamic analysis method which utilized a finite element model of a saturated porous seabed shield tunnel. The findings highlighted that different liquefaction mechanisms are observed in different types of the soil surrounding the tunnel. The thickness of the fine sand layer (FSL) surrounding the tunnel significantly affects seabed liquefaction depth and the tunnel's maximum bending moment (M_max). The highest M_max and damage probabilities were observed when the tunnel was entirely embedded in the FSL, whereas the smallest M_max and lowest damage probabilities occurred when the tunnel was partially within the sand and clay. This study could also provide some insights on seismic mitigation strategies in subsea shield tunnels and the soil type influences the timing of M_max occurrence and emphasized the critical role of seismic frequency in determining the tunnel's response.