Laboratory and theoretical evaluation of impact of packing density, particle shape, and uniformity coefficient on erodibility of coarse‐grained soil particles

Abstract

Sedimentation–including erosion, transport, and deposition of coarse-grained particles–is a primary and growingenvironmental, engineering, and agricultural issue around the world. Soil erosion occurs when the hydrodynamic force inducedby flowing water exceeds the geotechnical resistance of soils, as measured by critical shear stress for initiation of soil-particle motion.Even though various quantitative methods have been suggested with respect to different types of soil, the most widely acceptedformula to estimate critical shear stress for coarse-grained soil is a direct function of the median grain size of the soil particles;however, the erosion resistance of soils also varies with other geotechnical properties, such as packing density, particle shape,and uniformity coefficient. Thus, in this study, a combined rolling–lift model for particle detachment was derived based on theoret-ical analysis. A series of experimental flume tests were conducted with specimens prepared with standard soil types, as well aslaboratory-prepared mixtures of coarse-grained soil to validate the theoretical model and determine the effect of other geotechnicalproperties on the erosion characteristics of coarse grains, coupled with the effect of median particle size. The results indicated thatthe median grain size is the primary variable determining the resistance of coarse grains, but the critical shear stress alsovaries with the packing density of the soil matrix. In addition, angular particles show more erosion resistance than roundedparticles, and the erosion potential of a soil decreased when the grain is well graded (higher value of uniformity coefficient).Additionally, regression analysis was performed to quantify the effect of each parameter on the critical shear stress of coarse grains.