The role of particle type on suffusion and suffosion

Abstract

A distinction can usefully be made between suffusion, which describes the removal of fine particles by seepage flow from a body of soil without volume change, and suffosion, which is characterised by the removal of fine particles, accompanied by contractive volume change. Four pairs of gap-graded specimens were prepared, each pair comprising one glass bead specimen and one soil specimen with sub-angular particles, with nominally identical particle size distributions. The reconstituted specimens were isotropically consolidated to the same confining stress, and then subject to multi-stage upward seepage flow in a flexible wall permeameter. The glass beads and soil specimens with a finer fraction content of 0·20 exhibited suffusion. It appears that the susceptibility to suffusion of these specimens was not governed by particle type. Suffosion was evident in glass bead specimens with a finer fraction content of 0·35, but it was not triggered at an equal, or even larger, hydraulic gradient in soil specimens with nearly identical gradations. Particle type thus appears to be a factor governing the susceptibility to suffosion and should be considered when investigating this phenomenon.