Dynamic response of shield tunnels crossing ground fissures under near-field and far-field seismic excitations

Based on the engineering background of the Xi'an Metro Line 8 shield tunnel crossing the f3 ground fissure, this study systematically investigated the dynamic response characteristics of shield tunnels crossing ground fissures under near-field and far-field ground motions using a combined approach of a 1/20 shaking table test and numerical simulation. The results indicate that near-field ground motion (e.g., Chi-Chi record), due to its significant velocity pulse effect, leads to considerably higher peak accelerations in tunnel surrounding rock and structure, dynamic earth pressure, and bolt stress compared to far-field ground motion (e.g., El-Centro record). The ground fissure zone, as a geologically weak zone, amplifies the dynamic response differences between the hanging wall and footwall, particularly showing stress concentration and bolt axial force concentration at the vault and invert locations. The shaking table test revealed that the ring joint areas near the ground fissure are prone to tension failure and ring joint opening phenomena, with damage concentrated within a 10 m range from both the hanging wall and footwall of the ground fissure. The numerical simulation results verified and explained this phenomenon. The research results reveal the failure mechanism and characteristics of shield tunnels under near-field ground motion, emphasizing the importance of adopting an optimized design for ground fissure areas and near-field ground motion differences in seismic design, providing theoretical support and engineering reference for tunnel engineering seismic design under similar geological conditions.