Numerical Investigation on the Mechanism of Suffusion Evolution in a Tunnel Filling Medium Using the Four‐Field Strong Coupling Model

ABSTRACT Understanding the suffusion mechanism of a filling medium under multifield coupling is critical for analyzing and preventing water‐mud‐inrush disasters in tunnels. This study simplifies the representative elementary volume of the filling medium into two phases and four components by establishing a four‐field strong coupling model that includes pressure, concentration, porosity, and displacement fields. Considering spatial mapping, the suffusion process of the Longtan Tunnel in China was solved using weak form modeling. Based on the proposed suffusion model, the temporal and spatial correlation between suffusion and porosity was reinterpreted, and the temporal and spatial evolution laws of each field parameter during suffusion were analyzed. The danger level and the critical disaster time were determined. The results indicate that structural deformation is significant when investigating water‐mud‐inrush disaster mechanisms in filling media. The part with the strongest fluid‐structure interaction exhibited the most severe suffusion, showing a mutual causal relationship between the suffusion and the mechanical behavior of the filling medium.