Mechanical Characteristics and Collapse Process Simulation of Tunnel Under Seismic Loading During Construction: A Case Study of a Deep Diversion Tunnel in Southwest China

To investigate the collapse mechanisms of diversion tunnels during construction under seismic loading, a coupled continuum‐discrete numerical simulation method was employed. Before seismic excitation, the initial support system was generally stable, with minor damage observed at the arch foot and arch crown (damage coefficient <0.033). Under seismic loading, the support structure experienced significant stress redistribution, with the maximum principal stress reaching 67.7 MPa. Collapse initiated at the arch foot and propagated toward the arch crown, eventually forming through‐going cracks and inducing overall collapse of the upper tunnel section. The numerical simulation results show good agreement with the actual field results in terms of spatial distribution and damage characteristics. These findings clarify the mechanical response and collapse process of tunnels under seismic action during construction and provide practical guidance for dynamic safety evaluation and the design of seismic‐resistant tunnel support systems in earthquake‐prone regions.