The numerical difference between the liquid limit and the plastic limit; i.e., the difference between the water content of a fine-grained soil/water mixture at the boundary between its liquid and plastic states and the boundary between its plastic and brittle states, based on tests outlined by Atterberg and standardized by ASTM Standard D4318 – 05.
Syn. Plasticity number.
See Mitchell (1993).
See also activity, Atterberg limits, consistency number, liquid limit, plastic limit, shrinkage limit.