To address the complex seismic response of long tunnels longitudinally crossing heterogeneous geological formations, this study proposes a three-dimensional SV-wave oblique-incidence input method that accounts for the initial disturbance of the wave field induced by geological heterogeneity. The method transforms equivalent two-dimensional free-field responses into equivalent nodal forces applied at the boundaries of a 3D numerical model. A longitudinally heterogeneous “hard-soft-hard” site and tunnel system is established, in which the surrounding rock is modeled using the Mohr-Coulomb constitutive law, while the concrete lining is described by the concrete damaged plasticity model. The deformation patterns and failure mechanisms of the site-tunnel system under SV-wave excitation are systematically investigated. The results indicate that seismic damage under SV-wave loading is mainly concentrated in the soft-rock region. Failure of the soft surrounding rock induces pronounced sliding of the overlying hard rock, and the tunnel suffers severe damage due to the combined effects of soft-rock failure and strong ground shaking. Parametric analyses further show that smaller impedance ratios, larger soft-rock widths, and larger incidence angles significantly intensify the seismic response of the tunnel. The findings of this study provide valuable insights for the seismic design of tunnels crossing longitudinally heterogeneous geological formations.
Jiang et al. (Thu,) studied this question.