Seismic vulnerability of deep tunnels: numerical modeling for a fully nonlinear dynamic analysis

Fragility curves represent an operative tool to evaluate seismic vulnerability of different type of structures. In particular, analytical fragility curves seem especially suitable to deep tunnels because, as consequence of the availability of relatively few and well-documented case-histories, other approaches (e.g. empirical or judgmental) appear not always representative. Differently from above-ground facilities, for which are available different methodologies to simulate seismic damage, the lower seismic vulnerability of deep tunnels has generated a delay in the definition of damage models for this type of complex infrastructures. At present, the vulnerability assessment of tunnels is mainly based on empirical or judgmental fragility curves. This paper describes a 2D numerical model that, by using nonlinear constitutive models both for the tunnel lining and surrounding ground, allows to derive analytical fragility curves. The proposed damage model, which has been developed with the aim to simulate seismic damage on tunnels, is able to reproduce different failure mechanisms of the final lining and to quantify the accumulation of damage on the whole system during a seismic sequence.