Recent damages to tunnels during major earthquakes have prompted a deeper understanding of their vulnerability to seismic events. Fragility curves, which quantify the conditional probability of damage for a given ground shaking intensity, provide an effective tool for assessing this vulnerability. This study develops seismic fragility curves for shallow rock tunnels subjected to transverse ground motions using a performance-based approach that incorporates rock mass–tunnel structure interaction. Seismic response is evaluated through two-dimensional nonlinear time-history analyses, with rock mass behavior modeled using an elasto-plastic constitutive model. The tunnel lining is modeled as an elastic material and designed according to Indian Standard (IS) design guidelines. Damage state thresholds are defined by evaluating the exceedance of the lining's structural capacity. Fragility curves are generated as a function of effective peak ground acceleration (EPGA), employing Multi-stripe Analysis (MSA) to account for progressively increasing levels of seismic intensity and ground motion variability. This methodology is applied to various rock–tunnel configurations, providing a detailed assessment of their seismic vulnerability. The study emphasizes the limitations of current IS design guidelines in ensuring the seismic resilience of tunnels, highlighting the need for improved standards.
Chalavadi et al. (2026) studied this question.