Burial state controls the impact force and travelling distance of a movable cubic object in granular flows

Gravity-induced granular flows can bury and displace movable objects, thereby increasing the difficulty of post-hazard search and rescue. However, the fundamental mechanisms governing the impact response, downstream displacement, and burial of movable objects remain poorly understood. In this study, three-dimensional discrete element method (DEM) simulations are used to investigate the interaction between a granular flow and a movable cubic object. Analytical models are also proposed for predicting the travelling distance of the object. By varying the flow thickness h, normalized by the object height h c , and the impact velocity v, we identify two distinct regimes governed by the burial state of the object. In the unburied regime ( h/h c ≤ 1), the object remains exposed and is mainly transported by frontal impact and lateral flow deflection. In the buried regime ( h/h c > 1), the object is overtopped and progressively engulfed, leading to stronger coupling with the surrounding granular mass. Results reveal that the normalized impact force is predominantly controlled by the dimensionless flow discharge across both regimes. The travelling distance, however, exhibits clear regime dependence, following a power-law relationship with the dimensionless flow discharge in the unburied regime, while being better controlled by the Froude number in the buried regime. Analytical models developed for the two regimes successfully reproduce the computed travelling distances and provide a physically interpretable framework for estimating displaced-object locations.