An Experimental Parametric Study of Segregation in Cohesionless Soils of Embankment Dams

Abstract

Segregation is the haphazard separation of particle sizes, particularly in granular, cohesionless soils, which is preliminarily attributed to materials’ construction and handling processes. In embankment dams, in which precise control of soils’ gradation limits is essential, segregation may lead to defective functioning of various zones, such as filters, transitions, drains, etc. This treatment deals with quantifying the segregation propensity for cohesionless soils. A review of prominent segregation mechanisms and available rules and guidelines for minimizing segregation in embankment dam materials is presented. A simple test setup and procedure is introduced, by which segregation tests are performed on 26 gradations. Applying the testing method, a new segregation measure termed the “modified segregation index” is derived, which effectively quantifies the segregation propensity of cohesionless soils. Results reveal that an increase in moisture and granular-flow velocity decreases segregation, whereas segregation intensifies with an increase in gradation curvature and broadness. Also, a novel ternary diagram for determining segregation potential of granular soils based on particles size ranges is proposed, which is particularly useful for assessing segregation susceptibility in granular materials of existing dams.