Hydro-mechanical simulations aid demand-oriented design of slit dams for controlling debris flows, debris avalanches and rock avalanches

Slit dams are widely used for managing multiphase geophysical flows with diverse objectives. However, quantitatively linking dam configurations and flow properties to design indices remains particularly challenging for multiphase flows. This study performs systematic hydro-mechanical simulations of slit dams in arresting debris flows, debris avalanches, and rock avalanches, using a coupled computational fluid dynamics and discrete element method (CFD-DEM). Our high-fidelity simulations reasonably capture essential physics observed in experiments. Furthermore, unified design diagrams are compiled from multiple perspectives to quantitatively link flow properties (fluid contents and Fr conditions) and spillway width to crucial design indices, including overspilling dynamics, downstream momentum reduction ratio ζ, and retention efficiency. The results reveal that: i) Fr exhibits nonlinear correlations with these design indices that vary significantly during the impact regime transitions from pile-up to runup, due to the resulting changes in the size and shape jammed and mobilized domains; ii) Both ζ and retention efficiency negatively correlate with fluid content, Fr, and spillway width, with different priorities; and iii) Fluid contents and Fr jointly govern overspilling dynamics, while increasing spillway width can effectively reduce retention efficiency by changing trap patterns, including clogging, blockage and self-cleaning traps. This study and its findings contribute deep insights into multiphase flow-dam interactions and offer a unique physics-based dataset to facilitate the demand-oriented design of slit dams for controlling various anticipated flows.