Experimental Study of Imbrication and Clustering of Nonspherical Particles on a Rough Bed Surface

Abstract

Imbricate structures play an important role in river stability. However, quantitative experimental studies have been rarely conducted. In this study, four types of uniform particles with different degrees of flatness were used to investigate the imbrication and clustering phenomena of particles on the bed surface under different flow conditions. The results revealed the following: (1) The long-axis orientation of particles with different degrees of flatness tended to be perpendicular to the flow direction; (2) The average slope angles for the three nonspherical particles were 28°, 35°, and 40°, while spherical particles did not have a defined slope angle; (3) The larger the particle flatness was, the more sensitive it was to changes in the slope angle. When drag force was the main driving force, particles with larger slope angles were less stable; (4) Particles with greater flatness required stronger water flow to form clusters, whereas particles with lower flatness were more likely to form clusters at low flow rates; and (5) The long-axis direction of the clusters tended to align with the flow direction, and clusters formed by particles with less flatness were longer. Furthermore, under high-flow conditions, multiparticle clusters were more capable of maintaining bed stability than two-particle clusters. The greater the flatness of the particles, the higher was the stability of the clusters.