Prediction of the seismic behavior and backfilling scheme optimization of immersed tunnel based on the ruyifang project

The backfill soil is the first line of defense that ensures immersed tunnel's safety and stability, but its seismic performance has not been investigated in previous studies. This study employs the Ruyifang tunnel as its research object to determine the most dangerous cross-section. It establishes a two-dimensional soil-structure interaction system for complex sites to evaluate immersed tunnels' safety during earthquakes, clarify the structural failure mechanism, and optimize the backfilling scheme. In addition, this study investigates the tunnel element's response, damage, and stress under static and dynamic loads and obtains the impact of backfilling materials by considering plastic damage in structures, soil viscoelastic properties, and various backfilling schemes. The results showed that the tunnel section's stress has prominently distributed characteristics. Moreover, the structure exhibits tensile failure during ground motions, and the bottom of the side wall is the critical area. The inertial force is the primary factor affecting the seismic capacity at the overburden layer and flanks, while stiffness plays a vital role at the cushion. These dynamic properties and related backfilling technology can provide technical support for the anti-seismic design of immersed tunnels.