Impact dynamics of debris flow against rigid obstacle in laboratory experiments

Debris-flow impact against rigid obstacle involves instant redirection of flow velocity and elevation of flow depth, and could serve as a stringent approach for verification of the two-phase flow models. In this study, kinetic and dynamic behavior of debris-flow impact with varying flow regime has been analyzed on the basis of laboratory tests with distributed measurement. Debris flows interact with obstacle in the modes of vertical jet (deflected vertically) and momentum jump (reflected upstream). The experimental results are further adopted to verify the predictability of vertical jet model and momentum jump model. Our findings highlight that, due to the elevated confining stress in the impact area, the liquefaction ratio increases, resulting in a more “fluid-like” state of debris flow. The two analytical models could distinguish the runup height around the threshold Froude number 3–4. However, the impact loads under both modes could be very close, because the effective impact in the vertical jet mode only concentrates in the lower portion of runup height. The potential threat of flip-through impact (shock impact by a steep or concave wave front) should also be considered, as its impulse load could be much higher than the predicted load by vertical jet and momentum jump models. • Distributed measurement reveals the characteristics of impact pressure profile. • Liquefaction ratio increases during impact under elevated confining stress. • Impulse load of flip-through impact is much higher than traditional model prediction.