A Large Permeameter for Study of Internal Stability in Cohesionless Soils

Results are reported from the commissioning of a large rigid-walled permeameter that was designed to examine hydromechanical conditions prevailing at the onset of seepage-induced failure in soils with a potential for internal instability. A technique of slurry mixing and discrete deposition is used to reconstitute a homogeneous, saturated test specimen. The test specimen is consolidated and then subject to seepage flow, under head-control, in either a downward or upward direction. Two arrays of pressure transducers, located on opposite sides of the specimen, establish the variation of hydraulic gradient along the specimen. The device is configured with a top and bottom load cell, and frictionless loading ram, in order to assess the influence of side-wall friction and thereby establish the distribution of vertical effective stress along the length of the specimen. Observations of hydraulic gradient and effective stress enable a characterization of the onset of instability, which is localized within the specimen. Results of multi-stage tests on glass beads are reported that illustrate novel features of the permeameter and instrumentation, the utility of the specimen reconstitution technique and a novel approach for quantifying the onset of internal instability.