FLAC modeling of shallow tunnels under seismic action

Underground structures are generally considered less vulnerable to seismic action than above ground structures. However, there are practical cases in which this assertion needs to be verified. Even if dynamic effects are negligible, soil deformation may impose significant loads on the support structures, which have to be quantified. This paper addresses the modeling of tunnels at shallow depth subjected to earthquakes with FLAC. The issues related to the representation of the seismic input to be applied at the model base and dynamic boundary conditions are discussed. Comparisons with analytical solutions for elastic media are presented, showing the good performance of FLAC. Parametric studies are performed in order to evaluate the influence of tunnel depth, ground stiffness, soil non-homogeneity and non-elastic behavior.