Dynamic and pseudo-static analysis of shield tunnels in liquefiable ground with nearby aboveground structures

Abstract

The shield tunnel is one of the most prevalent types of urban underground tunnels, which frequently traverses liquefiable ground and comes in vicinity of aboveground structures, presenting substantial challenges for their seismic performance. This study employs high-fidelity dynamic numerical analysis and simplified pseudo-static analysis for shield tunnels with and without nearby aboveground structures in liquefiable ground, to identify the effect of aboveground structures on shield tunnel response, and propose a practical seismic analysis method for shield tunnels that can consider the influence of aboveground structures. In dynamic analysis, a plasticity constitutive model is employed to simulate liquefiable soil, and a modeling method capable of depicting the reinforced concrete segments and joints is employed to simulate shield tunnels. Results indicate that aboveground structures have a substantial influence on shield tunnels, which requires sufficient consideration in seismic design. An aboveground structure located directly over the tunnel can affect the shield tunnel's vertical displacement, lateral compressive deformation, joint deformation, and internal force. An aboveground structure located over to the side of the tunnel can affect the shield tunnel's horizontal displacement, rotation, racking deformation, joint deformation, and internal force. The traditional displacement-based pseudo-static analysis method is shown to perform poorly in evaluating in seismic response of shield tunnels in liquefiable ground with nearby aboveground structures, due to inadequate consideration for the complexities of structure-soil-tunnel interaction. A modified simplified method is proposed to account for the influence of liquefiable soil and aboveground structures based on the understanding of seismic behavior of the system.