Displacement and burial mechanisms of objects by granular flows: towards implications for post-disaster search and rescue

Flow-type landslides can displace and bury structures in hazard-prone areas. Such events create vast and poorly defined search zones that make rescue efforts challenging, especially if they must be completed within a critical 72-hour survival window. This study leverages a high fidelity multi-scale solver (coupled Material Point Method and Spheropolyhedron Discrete Element Method) to reveal the fundamental mechanisms of the displacement and transport of objects by granular flows. A parametric analysis is carried out to investigate the effects of flow velocity and depth, block density, basal friction, initial orientation, and block aspect ratio on the block displacement and transport based on entirely and partially submerged modes. A dimensionless number, the impact Froude number, is demonstrated to reliably predict the normalized travel distances of blocks for both modes. Travel distances inversely correlate with basal friction and block-to-flow density ratio, driven by frictional dissipation during deceleration. Orthogonal impacts maximize distances due to sustained momentum, increasing search challenges for perpendicular structures. Low-aspect-ratio blocks travel farther than slender ones owing to less overturning and velocity loss. A contour chart maps runout against Froude number, friction, and density, exposing high sensitivity in submerged regimes and serving as a practical guiding tool to enhance search and rescue operations.