How Flexible, Slit and Rigid Barriers Mitigate Two-Phase Geophysical Mass Flows: A Numerical Appraisal

Flexible, slit, and rigid barriers are common countermeasures to mitigate natural geophysical mass flows, but presently, quantitative comparisons of their performance are lacking, due to the challenges involved in accurately representing the multi-body and multi-phase interactions. This study presents a numerical appraisal on this issue using a physics-based coupled computational fluid dynamics and discrete element method (CFD-DEM). A geophysical flow is considered as a mixture of discrete gap-graded particles (DEM) and a continuous viscous slurry (CFD), whereas a permeable and deformable barrier structure can be modeled by DEM. The in-flow multiphase interactions and flow-barrier interactions can be rigorously modeled by a coupling scheme between DEM and CFD. Our numerical simulations reasonably capture both field and experimental observations on key features of flow-barrier interactions and barrier responses. The different intercepting mechanisms of three barriers via pile-up and runup modes are revealed by qualitative and quantitative characterizations. Flexible barriers perform the best under runup mode regarding much larger peak load reduction ratios (up to 89%) due to their high permeability and Fr-dependent load-deflection behavior. We further compile a barrier-specific design diagram that suggests existing analytical models calibrated by limited experiments may underestimate the peak impact for slit and rigid barriers due to their neglect of large solid particles in the impinging flows while leading to overestimations for flexible barriers owing to inappropriate representations of barrier permeability and structural deformability. Our findings may offer a basis for model improvements and developments in practical barrier selection and design.