Clogging Effects on the Impact Loading of Debris Flows against Beam-Type Check Dams

Beam-type check dams are widely adopted for debris flow mitigation due to their permeability and effective regulation capacity. However, particle clogging at dam openings during debris flow interception can fundamentally alter impact loading. In this study, a series of experiments are conducted to investigate the impact characteristics of debris flows on beam-type dams under clogging conditions, with emphasis on the coupled effects of bulk density, relative opening, and flume gradient. The results reveal that the impact behavior is governed by a strong coupling between structural permeability and flow dynamics, resulting in a trade-off between throughflow capacity and particle clogging propensity. The impact pressure distribution along the beams consistently exhibits a center-high and side-low pattern. Transverse non-uniformity increases with higher sediment concentration and flume gradient, whereas the relative opening primarily influences the overall impact magnitude. Particle clogging further enhances vertical heterogeneity due to flow climbing and backwater effects. The impact process involves a multistage, highly nonlinear fluid–structure interaction, evolving from an initial momentum-dominated impulsive regime to a clogging-controlled stage characterized by sustained and pulsating loading. The Froude number governs the initial impact intensity, while the evolution of particle clogging modulates both the magnitude and duration of impact pressure. A refined predictive model is developed by incorporating the throughflow–clogging coupling and linking the Froude number with a clogging criterion. This model enables improved estimation of impact pressure and effectively captures vertical non-uniformity. These findings provide new insights into the impact mechanisms of debris flows and offer a physically based framework for the design and optimization of beam-type dams.