The debris–barrier interaction issue has gained considerable attention among the engineering community, but most researches have only focused on the single-surge impact condition, with the multiple-surge impact mechanism still lacking clarity. However, multiple-surge impact is more typical in the field. Thus, we conduct some numerical simulations based on the discrete element method (DEM) and present a series of results that provide preliminary insights into the multiple-surge impact mechanism. The DEM model is firstly calibrated using physical experimental results and then used to investigate the flow kinematics, impact dynamics and energy evolution of the successive impact process. The results indicate that compared with single-surge conditions, the barrier is safer under multiple-surge impact as the deposition spreading distance is extended by 6–20% and the impact force is reduced by 6–30%. The dead zone formed by the previous surge behaves as a cushioning layer and a medium for momentum transfer. Three mechanisms of energy dissipation during surge–dead-zone interactions were identified: friction and penetration at the interaction face between the surge and dead zone, inelastic deformation of the dead zone, and inter-particle interaction within the surge. Each component was analyzed, which shows that inter-particle collision friction accounts for over 60% of the total energy loss during surge–dead-zone interaction. In addition, the performance of granular jump theory in predicting the multiple-surge impact force is assessed, and some possible modifications are proposed. Finally, some engineering implications from the presented numerical results are discussed.

The baffle design resisting dry granular flow is still impeded by the effect of the particle size distribution coupled with the influence of Froude characteristics on baffle performance – for example, the deceleration process and run-up process. Based on discrete-element method simulation, this study investigated the baffle deceleration and granular flow run-up. Baffle deceleration is controlled by the change of particle contact behaviour behind the baffle slits and is more sensitive to the particle size than the Froude characteristics of granular flow. Although the granular flow run-up height is also affected by the debris–slit interaction, it is mainly dominated by the flow climbing along the baffle, which is more sensitive to the Froude characteristics and stress-transfer mechanism. Bidisperse granular flow has more complex interaction with the baffle compared with monodisperse flow. The effect of material inhomogeneity on baffle performance depends on the particle content. For baffle design, the first array can be considered as a reference. The estimation of the baffle deceleration potential and height with consideration to unsteady dynamics and material inhomogeneity is also presented in this paper.