Analysis of tunnel behaviour under seismic loads using different numerical approaches

In this paper different approaches aimed at investigating the dynamic behaviour of circular tunnels in the transverse direction are presented. The analysed cases refer to a shallow tunnel built in an ideal soft clayey deposit excited by four different acceleration time histories characterised by significantly different frequency content. The adopted approaches include: 1) one-dimensional (1D) numerical analyses performed modelling the soil as a single phase visco-elastic non-linear medium, the results of which are then used to evaluate the input data for selected analytical solutions proposed in the literature (uncoupled approach); 2) 2D fully coupled Finite Element simulations adopting visco-elastic and visco-elasto-plastic constitutive assumptions for the soil and the lining (coupled approach); 3) 2D quasi-static Finite Element simulations adopting the same constitutive hypotheses of the fully coupled dynamic analyses. The three approaches, when a proper calibration of the soil parameters is undertaken, provide comparable results in the case of the visco-elastic assumption for the soil. The different constitutive hypotheses adopted in the 2D Finite Element simulations prove to play a significant role on the seismic-induced loads and curvature of the lining.