A Flexible Wall Permeameter for Investigating Suffusion and Suffosion

A flexible wall permeameter was described for the investigation of seepage-induced internal instability. The device comprises a double-walled triaxial cell, a base pedestal and top cap, a seepage control system, and instrumentation. A novel feature is the measurement of volume change during multistage seepage flow. Tests were reported on gradations of glass beads. Suffusion was observed as a seepage-induced increase in hydraulic conductivity, in the absence of substantial volumetric and axial strains, indicating particle migration. In contrast, suffosion was observed as a change in hydraulic conductivity, accompanied by substantial contractive volumetric strain with or without substantial axial strain, indicating rearrangement of the particle assembly. The test procedure yielded repeatable results. The resolution and accuracy of the measurement technique were sufficient to quantify the onset and progression of deformation in specimens with a volume of approximately 780 cm3. Considering the localized nature of the contractive volumetric deformation associated with suffosion, which can occur in the absence of axial deformation, measurement of volume change during multistage seepage flow proves necessary to avoid any misinterpretation of the phenomenological response to seepage flow.