Plastic Index Test

Plastic Index Definition of soil consistency

The plastic index of soil consistency is the strength with which soil materials are held together or the resistance of soils to deformation and rupture. Soil consistency is measured for wet, moist and dry soil samples. For wet soils, it is expressed as both stickiness and plasticity, as defined below. Soil consistency may be estimated in the field using simple tests or may be measured more accurately in the laboratory.

Note: in each case, indications will be obtained concerning the relative value of soil for fish-pond construction, particularly when the wet-soil consistency is determined. In the tests which follow (Sections 8.1 and 8.2), soils which are particularly good for pond construction are highlighted with two axterisks(**).

Determination of wet-soil consistency
Testing is done when the soil is saturated with water, as, for example, immediately after a good rainfall. First, determine stickiness, that is, the ability of soil materials to adhere to other objects. Then, determine plasticity, that is, the ability of soil materials to change shape, but not volume, continuously under the influence of a constant pressure and to retain the impressed shape when the pressure is removed.

Field test for stickiness of wet soil
Press a small amount of wet soil between your thumb and forefinger to see if it will stick to your fingers. Then slowly open your fingers. Rate the stickiness as follows:

1. Non-sticky, if no soil or practically no soil sticks to your fingers;

2. Slightly sticky, if the soil begins to stick to your fingers but comes off one or the other cleanly and does not stretch when the fingers are opened;

3. Sticky, if the soil sticks to both the thumb and forefinger and tends to stretch a little and pull apart rather than pulling free from your fingers

See other soil testing methods here

Check us out on Facebook here

Let the experts at CMT help you determine what the plasticity of your soil should be.

---

CONTACT US