Effects of SSI and lining corrosion on the seismic vulnerability of shallow circular tunnels

The paper presents a numerical approach for the construction of seismic fragility curves for shallow metro tunnels considering the soil-structure-interaction (SSI) and the aging effects due to corrosion of the lining reinforcement. The tunnel response under ground shaking is evaluated through 2D non-linear dynamic analyses, for increasing levels of seismic intensity. An elasto-plastic model is used to simulate the soil non-linear behavior under ground shaking, while the effects of lining mechanical properties, soil conditions and ground motion characteristics are also accounted for. The effect of corrosion on the lining behavior is encountered through proper modification of the lining strength properties. Damage state thresholds are defined based on the exceedance of the lining capacity. The fragility curves are estimated in terms of peak ground acceleration at the ground free field conditions for different time periods considering the associated uncertainties. The proposed approach is applied for the fragility assessment of selected soil-tunnel configurations. The derived fragility functions are compared with existing empirical and analytical fragility models, highlighting the important role of soil conditions and corrosion effects in the vulnerability of tunnel structures. The proposed fragility models contribute towards an advanced vulnerability and risk assessment of transportation systems and infrastructures.