A new framework to characterize and unify the impact load exerted by flow-type mass movements

A wide range of flow-type mass movements occur in nature. Depending on the solid fraction of these flows, they can be characterized as stream flows (flash floods), hyper-concentrated flows (debris floods), debris flows, and dry debris avalanches. A key scientific challenge in mitigating these hazards is estimating the impact force that they exert on protection structures. In this study, a new framework (N_fric - Fr² - \(\alpha\) relationship) is proposed to characterize and unify the impact behavior for a wide spectrum of flow-type mass movements. The friction number N_fric characterizes the ratio of grain-contact to fluid-viscous stresses for the wide range of flow types. Solid–fluid interaction regulates the pore fluid pressure, thereby governing the rheology of the flows and the degree of static loading exerted on a barrier. The Froude number Fr² (in squared form) macroscopically characterizes the flow inertia relative to the earth’s gravitational field. Finally, the dynamic pressure coefficient \(\alpha\) is used to quantify the impact force in a dimensionless manner. As compared to existing guidelines, which recommend a wide range of \(\alpha\) without considering the flow composition, the newly proposed framework in this study estimates the dynamic impact force by considering the effects of solid–fluid interaction. Findings from this study could further enhance the design of flow-type mass movement mitigation structures.