Shaking table test on the seismic response and reinforcement measures of double-arch tunnels in mountainous areas

Double-arch tunnels are commonly used in mountainous areas but are more vulnerable to earthquake damage than single-hole tunnels due to their large span and weak joints between the main tunnel and the centre wall. This study aims to understand the seismic response and damage characteristics of double-arch tunnels and provide design advice. A large-scale shaking table test was conducted in a high-intensity seismic zone, using strip reinforcement as seismic measures. Results show that peak accelerations of the inverted arch of tunnels increase as peak accelerations of seismic waves increase. Peak accelerations of the centre wall increase until peak loading accelerations achieve at 0.4 g. Large peak internal forces are mainly concentrated at the bottom of tunnels and near the centre wall. For the centre wall, bending moments are significantly influenced by structural abruptness at the junctions between the centre wall and the main tunnel, whereas axial forces are more evenly distributed in the centre wall. Seismic waves with high energy at low frequencies excite peak responses of strains and bending moments for the centre wall, especially at the wall top. Parts of the main tunnel connecting to the centre wall are in an adverse stress state, with the bottom and vault of tunnels being susceptible to cracking. Penetration cracks are likely to occur in the inverted arch and vault of tunnels as peak accelerations of seismic waves gradually increase. However, after penetration cracks appear in each of these two parts, further cracking is more likely to occur in the inverted arch, especially during strong seismic shaking. The overall forces in double-arch tunnels with strip reinforcement are significantly reduced, but there is little reduction in force for the bottom and outside of the lining.