Tunnel responses under reverse faulting: A semi-theoretical approach accounting for fault plane effects in soil-tunnel Interactions

Increasing numbers of underground infrastructures have been constructed or planned in seismically active and fault-prone regions, resulting in many inevitably intersecting active fault zones. Conventional theoretical approaches have typically simplified the active fault-tunnel system using a beam-foundation model, in which the surrounding soil is represented by equivalent soil springs with uniform stiffness. However, the present study demonstrated that, governed by the tunnel-fault intersection angle and interactions between the hanging wall and footwall, the stiffness of the equivalent soil springs varies significantly near the tunnel-fault intersection, showing a “hook effect”. To capture this effect, spatially varying stiffness distributions were derived through numerical methods and incorporated into a semi-theoretical framework. The active fault-tunnel system was divided into three equivalent sub-systems, and governing equations were formulated and coupled based on the Pasternak elastic foundation beam theory and classical elasticity solutions. Validation of the FE results confirmed the model’s accuracy across diverse geological conditions, with a greatly improved performance over the conventional approach. Furthermore, the proposed semi-theoretical framework was extended to yield two-dimensional results, providing not only consistency with the results of FE simulations, but also intuitive visualizations of tunnel responses under reverse faulting.