Recent laboratory studies of the erosive behavior of consolidated soils using the rotating cylinder apparatus showed that the stress required to initiate erosion is affected significantly by the amount and type of clay, pH, organic matter, temperature, water content, thixotropy, pore, and eroding fluid composition.

Using the concept of critical shear stress as measured using the rotating cylinder and the flume, a quantitative criteria for a dispersive clay system is defined as one with a critical shear stress, τc equals zero. Using this criterion, qualitative methods of predicting dispersive clays are examined. It is concluded that most of the qualitative tests used for the identification of dispersive clays suffer from the serious drawback of subjective identification criteria. Proper correlation of the results obtained from the qualitative tests for the condition of τc = 0 will provide a better basis for dispersive clay identification.

The potential use of “free swell test” as a predictive criterion is indicated.