Optical quantification of suffosion in plane strain physical models

Suffosion is a seepage-induced instability phenomenon whereby fines are eroded away through the constrictions formed by coarse particles, resulting in a reduction in soil volume and a change in hydraulic conductivity. In this study, upward seepage tests were performed on gap-graded soil containing coloured fines in a plane strain apparatus. A series of images was recorded through a transparent window to quantify the features of suffosion. The estimated cumulative eroded soil mass from image analysis was found to generally agree with independent macroscopic observations, indicating that optical analysis allows an easy identification of suffosion characteristics. For the tested soil, the fines were prone to be transported within an instant period of increasing hydraulic gradient, with few of them moving during the constant flow. Furthermore, the volume of the specimen was reduced due to suffosion, leading to an alternation of preferred coarse particle orientations in the observation field.