Study on the macro-meso mechanism of impact bearing failure of sandy mud in coastal tidal flats

The failure of coastal sandy mudflat silt under impact loading is essentially a macroscopic manifestation of mesoscopic particle motion and contact fabric evolution. Currently, the cross-scale correlation mechanism between macroscopic failure behavior and mesoscopic fabric evolution remains unclear. Therefore, taking sandy mud as the research object, this study combines laboratory experiments with discrete element simulations and develops a multi-dimensional mesoscopic analysis framework of “motion field-velocity field-contact fabric” through API secondary development, achieving cross-scale correlation between macro- and micro-scales. The results show: Macroscopically, increasing loading rate raises the peak force of the pressing plate, and under high-speed loading, the soil exhibits localized shear failure characteristics. Mesoscopically, the particle cumulative motion field reveals the evolution of energy dissipation paths and shear band boundaries; the velocity field further confirms differences in failure modes induced by different loading rates. Fabric analysis indicates that the contact vector exhibits a “double-lobe” distribution; high-speed loading suppresses the radial expansion of contact numbers, reduces horizontal radial contacts and coordination number, and induces localized penetration failure in the soil. Normalized contact force distribution shows that high loading rates induce force chains to shift from the principal stress direction to the radial direction, revealing an energy dissipation path dominated by inertial collisions, which explains the transition of macroscopic failure modes from a mesoscopic perspective. This study establishes a cross-scale correlation from macroscopic mechanics to mesoscopic particle motion and contact fabric evolution, providing key insights for the rapid and accurate assessment of mudflat geological bearing capacity.