The Journal of educational research

A valuable conceptual framework for the characterisation of seepage-induced internal instability was provided in the article under discussion, particularly for the ‘suffusion and suffosion’ phenomena. A few modifications are suggested here to clarify the definitions in the original paper

Viewing fluid flow inside a granular medium

This paper describes preliminary tests from a ‘transparent soil permeameter’ that has been developed to study the mechanisms that occur during internal erosion in filter materials for embankment dams. The laboratory-based experiments utilise an optical approach where glass particles are used in place of soil, and optically matched oil is used in place of water. The refractive index matching of the fluid and solid enables a two-dimensional “slice” or plane of particles and fluid to be viewed inside the permeameter, away from its walls via a laser sheet and captured by digital camera. The developed set up has already been tested and showed that optically matched glass and oil can behave similarly to soil and water materials as used in previous laboratory testing. In this study we present a flow characterization within a refractive index matched medium made of glass beads. To this end a small amount of fluid tracers is seeded inside the fluid and the velocity field inside the porous media is obtained using PIV measurements