Three-Dimensional Active and Passive Seismic Stability Analysis of Shallow Shield Tunnel Faces

Abstract

Comprehensive assessment of the active/passive seismic stability of shallow tunnel faces is an urgent and complex task. This work establishes a promising three-dimensional (3D) approach using upper-bound limit analysis to evaluate the active and passive seismic stability of shallow shield tunnel faces. The outcrop failure model and inside failure model are provided for active failure analysis. To capture the spatiotemporal variations of seismic loading, the pseudodynamic approach is employed to assess the limit active and passive support pressures. Comparisons with published studies and numerical simulations demonstrate that the proposed 3D approach greatly improves existing 2D results for limit active and passive support pressures. A detailed investigation is then conducted to analyze the effects of pseudodynamic parameters, surface surcharge, and buried depth on face stability of shallow tunnels. Finally, the proposed approach is further tested by conducting the seismic face stability analysis of Changsha Metro 2 tunnel based on actual seismic response. The results indicate that the surface surcharge has a greater influence on limit passive support pressure than limit active support pressure, and increasing of buried depth leads to a larger safety range of limit support pressure. Active and passive face failure of shallow tunnels under earthquakes can endanger the safety of tunnels and ground surfaces, leading to severe casualties and property losses. Determination of limit support pressures under seismic forces is a critical task in shield tunnel construction. This work establishes an approach to assess 3D active and passive seismic stability of shallow shield tunnel faces. Time–space variations of seismic loading are incorporated to accurately determine limit active and passive support pressures using pseudodynamic approach. Effects of seismic parameters, surface surcharge, and buried depth on face stability of shallow tunnels are then presented and discussed. Finally, the proposed approach is tested by conducting the seismic face stability analysis of Changsha Metro 2 tunnel based on actual seismic response. The results indicate that surface surcharge has a greater influence on limit passive support pressure compared with limit active support pressure, and increasing buried depth leads to a larger safety range of limit support pressure. The proposed approach determines a safety range of limit support pressures more accurately for shallow shield tunnels during earthquakes.