Influence of trapping efficiency on the pile-up geometry of granular flows behind slit dams

The post spacing of slit dams is a key parameter that controls the trapping efficiency of these open-type countermeasures. In this study we conduct flume experiments of quasi-monodisperse spherical particles passing through slits to investigate the relationship between the trapping efficiency and the pile-up geometry, as well as the impact of the latter on the interaction between granular flows and slit dams. The ratio of the slit width relative to the particle size b/d is varied while the flume inclination is held constant. Tests reveal that at a critical ratio b/d∼2.3 trapping is most unstable. The trapping efficiency influences the geometry of the granular pile-up that deposits behind the dam after it has been jammed. When >52% of the granular mass is trapped (occurring at b/d≤2.3), the height of the final deposit changes with the trapping efficiency, whereas below this threshold value (when b/d≥3.1)the flow-wise length becomes more sensitive to the trapping. Impact force measurements further shed light on the mechanisms relating the trapping efficiency and the geometry and their effect on the total force fluctuations. •Flume experiments of granular materials impacting slit dams reveal a critical relative post spacing of b/d∼2.3 at which the trapping is considered most unstable.•The deposit geometry depends on the trapping efficiency. When the efficiency is >52 %, deposit height is sensitive to it but below this threshold only the flow-wise length changes.•The total impact force reflects the pile-up process and geometry. The trapping efficiency influences the magnitude of the impact force and its evolution as particles exit from the slits.