Determining the Plastic Limit and Plasticity Index of Soil - Soil Properties: Testing, Measurement, and Evaluation - page 96

The plastic limit is the lower boundary range of the plastic behav-
ior of a given soil. It tends to increase in numerical value as grain size
decreases. Its primary use is in association with the other Atterberg
limits in soil identification and classification.

REFERENCE

[1] ASTM, 2007 Annual Book of ASTM Standards , West Conshohocken, PA,

2007. Copyright, American Society for Testing and Materials, 100 Barr
Harbor Drive, West Conshohocken, PA 19428-2959. Reprinted with per-
mission.