Seismic response of cross-passages between parallel tunnels with varied connection rigidities in centrifuge model tests

Traffic tunnels normally have cross-passages between parallel tunnels with close proximity to facilitate materials/human transportation and evacuation. It is obviously essential to maintain the structural integrity and functionality of cross passages under extreme conditions, such as seismic events. Due to the spatial configuration of the cross passage, its connection to running tunnels would be a key point to its seismic response and the subject of research in terms of enhancing the seismic resilience. This study adopted centrifugal model tests to investigate three types of connections with different rigidities and their influences on seismic performance of tunnel-cross passage structures in subway systems: flexible connections, rigid connections, and Shape Memory Alloy (SMA) connections, reflecting respectively cast-in-site concrete, segment assembling, and an innovative connection. The results indicated that regardless of the connection method used, the maximum strain at the tunnel-cross passage junction consistently occurs at the middle of the junction. The flexible connection exhibited a significantly lower maximum strain compared to the rigid connection, while the rigid connection demonstrated a higher degree of structural integrity. The SMA connection, with its energy absorption and dissipation capabilities, maintained structural integrity comparable to that of the rigid connection while exhibiting a lower maximum strain and significantly reducing stress concentration in localized areas of the tunnel-cross passage structure.