Numerical assessments of the influences of soil–boulder mixed flow impact on downstream facilities

Rapid soil–boulder mixed flow commonly occurs in steep mountainous regions and has the potential to damage critical infrastructures. Baffles are typically used as flow-impeding structures to mitigate the destructive power of this natural hazard. Although material heterogeneity plays an important role in these processes, the influence of particle size difference, particularly boulders, has often been overlooked due to its complex multi-scale nature. Therefore, we conduct various numerical examples by a Discrete Element Material Point Method, previously introduced by the authors, to provide insights into the effects of boulders. The results reveal that the collisions and interactions between different components (soils, boulders and baffles) can dissipate kinetic energy and reassemble the spatial distribution of soils and boulders. The simulations illustrate how the average impact force on the baffle becomes non-symmetric when there are boulders in the mixed flow and more significant when the rock volume fraction increases. Moreover, it is shown that increasing the baffle array is an effective way to reduce the velocity of mixed flow and dissipate the kinetic energy of whole system. Finally, the results obtained from this study are beneficial for designing optimal baffles and mitigating natural hazards.