Dynamic response and failure characteristics of twin-arch tunnels reinforced with steel strips under pulse-like ground motions: Insights from shaking table tests

Abstract

Twin-arch tunnels are widely employed in mountainous regions worldwide due to terrain constraints and alignment difficulties. However, when crossing near-fault seismic zones, these structures face significant seismic challenges. Compared with far-field earthquakes, near-fault earthquakes are characterized by long- period, high-velocity pulse motions, which impose more severe impacts on tunnel structures. Compared with conventional single-hole tunnels, twin-arch tunnels exhibit larger spans, weaker connections linking the main lining to the central wall, and unfavourable width-to-height ratios of the central wall, making their seismic resistance more vulnerable. Therefore, this study focuses on a near-fault twin-arch tunnel project and performs a shaking table model test to examine the dynamic response of the twin-arch tunnel and the performance of steel strip reinforcement under pulse-like ground motions. The results show that the acceleration amplification factor increases with elevation but decreases above the twin-arch tunnel with higher peak ground acceleration due to plastic flow damping. Conversely, it increases below the tunnel as the soil becomes denser and dissipates less energy. Under pulse-like ground motion, the acceleration amplification factor beneath the tunnel is lower than that under ordinary ground motion. The central wall mainly transmits seismic inertial forces, with its acceleration influenced by structural connections, whereas dynamic amplification in the inverted arch results from energy concentration because of its geometry. The arch shoulder adjacent to the central wall experiences the highest peak soil pressure. Pulse-like ground motion has a stronger impact on the soil above the tunnel and induces higher peak strains and internal forces than ordinary ground motion does. Steel strip reinforcement significantly reduces the overall response force of the twin-arch tunnel to pulse-like ground motion but increases the strain concentration at the reinforced–unreinforced junctions.