1.1 This test method, when used in conjunction with a test performed by Test Method D422 on a duplicate soil sample, provides an indication of the natural dispersive characteristics of clay soils (1).

1.2 This test method is applicable only to soils with a plasticity index greater than 4 as determined in accordance with Test Method D4318 and more than 12 % of the soil fraction finer than 5-μm as determined in accordance with Test Method D422 (2).

1.3 This test method is similar to Test Method D422, except that this method covers the determination of percent of soil particles smaller than 5-μm in diameter in a soil-water suspension without mechanical agitation and to which no dispersing agent has been added.

1.4 The amount of particles smaller than 5-μm determined by this method compared with the total amount of particles smaller than 5-μm determined by Test Method D422 is a measure of the dispersive characteristics of the soil.

1.5 This test method may not identify all dispersive clay soils. Pinholes (Test Method D4647 and crumb tests, or both, (3-5)or the analysis of pore water extract (4-7) may be performed to help verify dispersion.

1.6 All observed and calculated values shall conform to the guidelines for significant digits and rounding established in Practice D6026.

1.7 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.

1.8 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.