Simulated seismic response analysis of subway tunnels under complex geological conditions of obliquely incident seismic SV waves

Abstract

To investigate the seismic performance of simulated subway tunnels under complex geological conditions of obliquely incident earthquake excitations, a new input method for oblique incidence of SV waves with arbitrary incident angles in 3D space has been proposed. The method relies on explicit finite element method (EFEM) and viscous-spring artificial boundary (VSAB) condition, which simultaneously considers soil-structure interaction, surrounding soil characteristics, and seismic wave incident characteristics. It is applied and verified based on the seismic wave theory. The overall numerical model of subway tunnel and soil foundation is then established, and the dynamic response of subway tunnel in soft and hard interbedded soils under oblique incidence of SV waves is systematically analyzed. The obtained simulated results indicate that the dynamic response of each point in subway tunnel is decreased by increasing incident SV wave angle. It is also found that the dynamic responses of the site interbedded by soft and hard soils are significantly higher than that in other points of the site at the same incident angle, indicating that the mentioned zone has weak seismic resistance. In addition, the dynamic response of each point in tunnel structure tends to become closer when the bulk moduli of soft and hard soils are getting close. The displacement and moment of the site interbedded by soft and hard soils are reduced by increasing the thickness of lining structure, therefore improving the seismic resistance of the tunnel. The results of parametric study show that these factors could have significant influences on the seismic responses of tunnel structures during earthquake and should be considered during earthquake-resistant design of subway tunnels under complex geological conditions.