ABSTRACT
Two-dimensional dynamic numerical analyses are conducted to assess the seismic response of deep tunnels located far from the seismic source, under drained or undrained loading conditions. It is assumed that the liner remains elastic and that plane strain conditions apply. An elastoplastic constitutive model is proposed to simulate the nonlinear behavior and excess pore pressures accumulation in the ground with cycles of loading. The results show negligible effect of input frequency on tunnel distortions for frequencies smaller than 5 Hz; that is, for ratios between wavelength and tunnel opening larger than about eight to ten. The results also show that undrained conditions, compared with drained conditions, tend to reduce deformations for flexible liners and increase them for stiffer tunnels, when no accumulation of pore pressures with cycles of loading is assumed. However, when pore pressures increase with number of cycles, the differences between drained and undrained loading are reduced.
