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 similar to 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.