Consistency is the ability of soil to stick together and resist fragmentation. It is of rough use in predicting cultivation problems and the engineering of foundations. Consistency is measured at three moisture conditions: air-dry, moist and wet. The measures of consistency border on subjective as they employ the “feel” of the soil in those states. A soil’s resistance to fragmentation and crumbling is assessed in the dry state by rubbing the sample. Its resistance to shearing forces is assessed in the moist state by thumb and finger pressure. Finally, a soil’s plasticity is measured in the wet state by moulding with the hand.
The terms used to describe a soil in those three moisture states and a last state of no agricultural value are as follows:
- Consistency of Dry Soil: loose, soft, hard, extremely hard
- Consistency of Moist Soil: loose, friable, firm, extremely firm
- Consistency of Wet Soil: non-sticky, sticky or non-plastic, plastic
- Consistency of Cemented Soil: weakly cemented, indurated (cemented)
Soil consistency is useful in estimating the ability of soil to support buildings and roads. More precise measures of soil strength are often made prior to construction.