Numerical Analysis of the Effect of Tunnel Span on the Dynamic Response of Tunnel under Strong Stress Waves

Abstract

Span significantly impacts tunnel bearing capacity, and this study investigates its influence on the dynamic response of straight-walled arch tunnels under strong ground impact loads. A dynamic finite element model is established to simulate the mechanical behavior of the tunnel under static and dynamic coupling conditions. The plastic zone evolution, peak particle velocity distribution, and tunnel displacement characteristics are analyzed using the dynamic finite element method for a tunnel subjected to self-gravitational load and strong ground impact load. Results indicate that when the span is relatively small, the plastic zone is concentrated at the straight wall position. As the tunnel span increases, the plastic zone expands from the straight wall location towards the vault top, with an additional plastic zone parallel to the vault forming above the vault top. Moreover, increasing burial depth effectively inhibits the generation of the plastic zone parallel to the vault. With increasing span, both the maximum relative displacement between the vault and arch base and the maximum irreversible relative displacement increase. However, increasing tunnel depth leads to an increase in the maximum relative displacement but a decrease in the maximum irreversible relative displacement. The maximum mass velocity around the tunnel becomes increasingly inhomogeneous with larger spans. Particle velocity at the tunnel top increases with span, while particle velocity at the tunnel bottom decreases with increased tunnel depth. A combined criterion involving plastic zone distribution, particle velocity patterns, and displacement characteristics is recommended for evaluating tunnel safety performance