LAUSR

Abstract The presence of a soft soil layer can influence the propagation of incoming wave from the bedrock, undoubtedly modifying the ground motions and soil dynamic behavior. Despite its importance, the effect of an underlying soft soil layer on the seismic behavior of tunnels is not well known. In this paper, the analytical study, as well as numerical analysis is used to characterize the underlying soft soil layer-tunnel interaction problem. The analytical solution assumes the plane SH wave vertically propagating through an elastic soft interlayer. The soil plasticity is considered in the numerical study with a visco-elasto-plastic constitutive model following the Mohr-Coulomb shear failure criterion combined with the stiffness degradation. The effects of the input motion intensity, relative thickness, relative stiffness and buried depth of the soft layer are taken into account. The analyses highlight the possible beneficial effects on the site seismic response and tunnel seismic behavior due to the presence of the soft soil layer. The soft soil layer generally amplifies the long periods whereas de-amplifies the short periods of the input ground motion, while the responses in terms of acceleration, strain and Arias intensity at the tunnel position are reduced. In addition, the quantitative relationships between the modification ratios of the dynamic internal forces and soft soil layer parameters are presented.