ABSTRACT
Dispersive soils are those which normally deflocculate or are easily disaggregated when exposed to water of low salt concentration. According to Bell and Maud (1994), Dispersion occurs in soils when the repulsive forces between clay particles exceed the attractive forces. This brings about deflocculation, so that when exposed to relatively pure water, the particles repel each other. This is actually the basis for adding a “dispersing agent” to the soil suspension when conducting the hydrometer or pipette test to determine the grain-size distribution of fine-grained soils.
In this test, developed in the 1940s by the U.S. Soil Conservation Service (Sherard et al. 1976; Decker & Dunnigan 1977), a standard hydrometer test is performed with dispersing agent and mixing. The test is then performed on an identical soil specimen, but in this case no dispersing agent is used and there is no agitation. The degree of Dispersion is defined by comparing the percentage of soil particles < 0.005 mm in the test with dispersing agent to the percent < 0.005 mm without dispersing agent.
