ASTM International

Standard Test Methods for Determining Dispersive Characteristics of Clayey Soils by the Crumb Test
 N D6572

Annotation

Two test methods are provided to give a qualitative indication of the natural dispersive characteristics of clayey soils: Method A and Method B.

Method A—Procedure for Natural Soil Crumbs described in 10.2.

Method B—Procedure for Remolded Soil Crumbs described in 10.3.

The crumb test, while a good, quick indication of dispersive soil, should usually be run in conjunction with a pinhole test and a double hydrometer test, Test Methods D4647 and D4221, respectively.

The crumb test has some limitations in its usefulness as an indicator of dispersive soil.Adispersive soil may sometimes give a non-dispersive reaction in the crumb test. Soils containing kaolinite with known field dispersion problems, have shown non-dispersive reactions in the crumb test (1).2 However, if the crumb test indicates dispersion, the soil is probably dispersive.

These test methods are not applicable for soils with 12 % or less of the particles passing 0.005 mm and having a plasticity index less than or equal to 8, as determined by Test Method D4318.

Oven-dried soil should not be used to prepare crumb test specimens, as irreversible changes could occur to the soil pore-water physicochemical properties responsible for dispersion (2).

NOTE 1—In some cases, the results of the pinhole, crumb, and double-hydrometer test methods may disagree. The crumb test is a better indicator of dispersive soils than of non-dispersive soils (3). 1.6 All observed and calculated values shall conform to the guidelines for significant digits and rounding established in Practice D6026.