Table 1.

Soil classification in relation to plasticity index. From NHBC Chapter 4.2 (27)

Plasticity index**Shrinkage* potential
20 - 40%Medium
10 - 20%Low
  • * Shrinkable soils are those containing more than 35% fine particles (silt and clay) and have a plasticity index of more than 10%.

  • ** Plasticity index is related to shrinkage potential as shown. If the shrinkage potential is unknown, high shrinkage potential should be assumed.