Dynamic response and failure mechanism of rural masonry structures impacted by debris flow containing boulders

Rural masonry structures in mountainous regions are highly vulnerable to debris flow impacts. However, their dynamic failure mechanisms remain poorly quantified. To address this knowledge gap and enhance the debris flow resilience of such structures in the Three Gorges Reservoir Area, a Fluid-Structure Interaction model was established and validated using ANSYS Workbench. The model simulated the impact of debris flows containing boulders and incorporated the Drucker-Prager constitutive model for the masonry material. Parametric analysis revealed a bimodal dynamic response, characterized by the peak boulder force lagging behind the peak slurry force. A critical flow velocity of 5 m/s was identified: above this threshold, slurry force dominated (Fslurry > Fboulder), while below it, the boulder force was greater (Fslurry < Fboulder). The critical failure parameters were quantified as follows: At a flow depth of 1.5 m, the critical velocities for local and global collapse were 5 m/s and 9 m/s, respectively. Conversely, at a flow velocity of 5 m/s, the critical depth for severe damage was 3 m. Stress analysis showed that boulder impact induced significant stress concentration, with the peak von Mises stress (σboulder) 114.29% higher than that from the slurry (σslurry). A damage grading standard and corresponding displacement prediction formulas were proposed based on the inter-story displacement angle. Collectively, these findings provide a theoretical and practical foundation for designing rural masonry structures that are resilient to debris flow disasters.